7 Modified Sine Wave Inverter Circuits Explored - 100W to 3kVA

The following article presents 7 interesting modified sine wave inverter designs with exhaustive descriptions regarding its construction procedure, circuit diagram, waveform output and detailed parts lists. The designs are intended for learning and building experimental projects by engineers and students.

Here we discuss different varieties of modified designs ranging from a modest 100 watt to a massive 3 Kva power output model.

Let's investigate the first modified inverter design which is rather simple and uses a single IC 4017 for processing the required modified waveform.

If you are looking for an easy to build modified sine wave power inverter circuit, then perhaps the following concept will interest you. It looks astonishingly simple and low cost with an output that’s to a very extent is comparable with other more sophisticated sine wave counterparts.

How Modified Inverters Work

Folks who are new to electronics may get a bit confused regarding the difference between a square wave and a modified square wave inverter. It may be understood through the following brief explanation:

As we all know an inverter will always generate an alternating current (AC) similar to our domestic AC line voltage so that it can replace it during power failures. An AC in simple words is basically a rise and fall of voltage of a particular magnitude.

However, ideally this AC is supposed to as close as possible to a sinewave as shown below:

sinusoidal waveform, sinewave

Basic Difference between Sine waveform and Square Waveform

This rise and fall of voltage happens at a particular rate i.e. at a particular number of times per second, known as its frequency. So for example a 50 Hz AC means 50 cycles or 50 ups and downs of a particular voltage in one second.

In a sine wave AC as found in our normal domestic mains outlet the above rise and fall of voltage is in the form of a sinusoidal curve, i.e. its pattern gradually varies with time and thus is not sudden or abrupt. Such smooth transitions in the AC waveform becomes very suitable and a recommended type of supply for the many common electronic gadgets like TVs , music systems , Refrigerators, motors etc.

However, in a square wave pattern the voltage ups and downs are instant and sudden. Such immediate rise and fall of potential creates sharp spikes at the edges of each wave and thus becomes very undesirable and unsuitable for sophisticated electronic equipment. Therefore it is always dangerous to operate them through a Square weave inverter supply.

comparing modified sine with pure sinewave

Modified Waveform

In a modified square wave design as shown above, the square waveform shape basically remains the same but the size of each section of the wave-form is appropriately dimensioned so that its average value matches closely to an AC waveform’s average value.

As you can see there's a proportionate amount of gap or "dead time" between each square blocks, these gaps ultimately help to shape up these square waves into sinewave like output (albeit crudely).

And what is responsible for adjusting these dimensioned square waves into sinewave like features? Well, it is the inherent characteristic of the transformer's magnetic induction which effectively carve the "dead time" transitions between the square wave blocks into a sinewave looking waves, as shown below:

creating modified sine waveform

In all the 7 designs explained below we try to implement this theory and ensure that the RMS value of the square waves are appropriate controlled by chopping the 330V peaks into 220V modified RMS. The same can be applied for 120V AC by chopping down the 160 peaks.


For the first modified inverter project we yet again take the help of the evergreen versatile IC 4017.

We know that when a clock input is applied to its pin #14, the IC produces a shifting cycle logic high pulses through its 10 output pins.

Looking at the circuit diagram we find that the pin outs of the IC are terminated to supply the base of the output transistors such that they conduct after every alternate output pulse from the IC.

This happens simply because the bases of the transistors are connected alternately to the IC pin outs and the intermediate pin-out connections are just eliminated or kept open.

The transformer windings which are connected to the transistor’s collector respond to the alternate transistor switching and produce a stepped up AC at its output having a waveform exactly as shown in the diagram.

The output of this Modified sine wave power inverter is although not quite comparable to the output of a pure sine wave inverter but definitely will be far better than that of an ordinary square wave inverter. Moreover the idea is very easy and cheap to build.

simplest modified sinewave inverter circuit using IC 4017 and IC 555

Minimum Specifications

Input: 12V from Lead Acid Battery, for example 12V 7Ah battery

Output: 220V or 120V depending on transformer rating

Waveform : Modified sinewave

Feedback from one of the dedicated viewers of this blog, Ms Sarah

Hello Swagatam,

This is what I obtained from the output of IC2 post resistors R4 and R5. As I earlier said I expected to have a bipolar wave. One in positive and the other in negative . to simulate an ac wave cycle. I hope this picture will help. I need a way forward please.


oscilloscope trace for a modified waveform

My Reply:

Hello Sarah,

The IC outputs will not show bipolar waves since the signals from these outputs are intended for identical N type transistors and from a single supply....it's the transformer which is responsible for creating the bipolar wave at its output since it's configured with a push-pull topology using a center tap ....so what you are seeing across R4 and R5 are correct waveform. Please check the waveform at the output of the transformer for verifying the bipolar nature of the waveform.

The Second Design

This second in the list is a unique modified sine wave inverter concept also designed me. The entire unit along with the oscillator stage and the output stage can be easily built by any electronic enthusiast at home. The present designed will be easily able to support 500 VA of output load.

Let's try to understand the circuit functioning in details:

The Oscillator Stage:

Looking at the circuit diagram above, we see a clever circuit design comprising both, the oscillator as well as the PWM optimization feature included.

Here, the gates N1 and N2 are wired up as an oscillator, which primarily generates perfectly uniform square wave pulses at its output. The frequency is set by adjusting values of the associated 100K and the 0.01 uF capacitor. In this design it is fixed at the rate of around 50 Hz. The values can be altered appropriately for getting a 60 Hz output.

The output from the oscillator is fed to the buffer stage consisting of four parallel and alternately arranged NOT gates. The buffers are used for sustaining perfect pulses and for avoiding degradation.

The output from the buffer is applied to the driver stages, where the two high-power darlington transistors take the responsibility of amplifying the received pulses, so that it can be finally fed to the output stage of this 500 VA inverter design.

Until this point the frequency is just an ordinary square wave. However the introduction of the IC 555 stage entirely changes the scenario.

The IC 555 and its associated components are configured as a simple PWM generator. The mark-space ratio of the PWM can be discretely adjusted with the help of the pot 100K.

The PWM output is integrated to the output of the oscillator stage via a diode. This arrangement makes sure that the generated square wave pulses are broken into pieces or chopped as per the setting of the PWM pulses.

This helps in reducing the total RMS value of the square wave pulses and optimize them as close as possible to a sine wave RMS value.

The pulses generated at the bases of the driver transistors are thus perfectly modified to resemble sine wave forms technically.

IC 4049 based modified sinewave inverter circuit

The Output Stage:

The output stage is quite straight forward in its design. The two winding of the transformer are configured to the two individual channels, consisting of banks of power transistors.

The power transistors at both the limbs are arranged in parallel to increase the overall current through the winding so as to produce the desired 500 watts of power.

However to restrict thermal runaway situations with the parallel connections, the transistors are connected with a low value, high wattage wire wound resistor at their emitters. This inhibits any single transistor from getting over loaded and fall into the above situation.

The bases of the assembly are integrated to the driver stage discussed in the previous section.

how to connect power BJTs with transformer

The battery is connected across the center tap and the ground of the transformer and also to the relevant points in the circuit.

Switching ON power immediately starts the inverter, providing rich modified sine wave AC at its output, ready to be used with any load upto 500 VA.

The component details are supplied in the diagram itself.

The above design can also be modified into a 500 watt PWM controlled mosfet sine wave inverter by replacing the driver transistors simply by a few mosfets. The design shown below would provide about 150 watts of power, for obtaining 500 watts, more number of mosfets may be required to be connected in parallel with the existing two mosfets.

500 watt modified inverter

Inverter#3 using a 4093 IC for the Modified Results

The PWM controlled modified sine wave inverter circuit presented below is our 3rd contender, it uses just a single 4093 for the specified functions.

The IC consists of four NAND gates, out of which two are wired up as oscillators while the remaining two as buffers.

The oscillators are integrated in such a way that the high frequency from one of the oscillators interacts with the output of the other, generating chopped square waves whose RMS value can be well optimized to match the regular sine waveforms.Inverter designs are not always easy to understand or build, especially so when it's as complex as modified sine wave types. However the concept discussed here utilizes just a single IC 4093 for handling all the required complications. Let's learn how simple it is to build.

Parts you will Ned to Build this 200 Watt Inverter Circuit

All Resistors are 1/4 watt, 5 %, unless otherwise specified.

R1 = 1 M for 50 Hz and 830 K for 60 Hz
R2 = 1 K,
R3 = 1 M,
R4 = 1 K,
R5, R8, R9 = 470 Ohms,
R6, R7 = 100 Ohms, 5 Watt,
VR 1 = 100 K,
C1, C2 = 0.022 uF, Ceramic Disc,
C3 = 0.1, disc ceramic
T1, T4 = TIP 122
T3, T2 = BDY 29,
N1, N2, N3, N4 = IC 4093,
D1, D1, D4, D5 = 1N4007,
D3, D2 = 1N5408,

Transformer = 12 -0 – 12 volts, current from 2 to 20 Amps as desired, output voltage can be 120 or 230 volts as per country specifications.

Battery = 12 volts, typically a 32 AH type, as used in cars is recommended.

nand gate based 750vA modified inverter circuit

Simulation and Working

The proposed design of a 200 watt modified sine wave inverter obtains its modified output by discretely “cutting” the basic square wave pulses into smaller sections of rectangular pulses. The function resembles to a PWM control, commonly associated with IC 555.

However, here the duty cycles cannot be varied separately and is kept equal throughout the available variation range. The limitation does not affect the PWM function by much, since here we are only concerned in keeping the RMS value of the output close to its sine wave counter, which is executed satisfactory through the existing configuration.

Referring to the circuit diagram, we can see that the entire electronics hovers around a single active part – the IC 4093.

It consists of four individual NAND Schmitt gates, all of them have been engaged for the required functions.

N1 along with R1, R2 and C1 forms a classic CMOS Schmitt trgger type of oscillator where the gate is typically configured as an inverter or a NOT gate.

The pulses generated from this oscillator stage are square waves which forms the basic driving pulses of the circuit. N3 and N4 are wired up as buffers and are used for driving the output devices in tandem.

However these are ordinary square wave pulses and do not constitute the modified version of the system.

We can easily use the above pulses solely for driving our inverter, but the result would be an ordinary square wave inverter, not suitable for operating sophisticated electronic gadgets.

The reason behind this is that, square waves may differ greatly from the sine waveforms, especially as far as their RMS values are concerned.

Therefore, the idea is to modify the generated square waveforms so that its RMS value closely matches with a sine waveform. To do this we need to dimension the individual square waveforms through some external intervention.

The section comprising N2, along with the other associated parts C2, R4 and VR1, forms another similar oscillator like N1. However this oscillator produces higher frequencies which are tall rectangular shaped.

The rectangular output from N2 is fed to the basic input source of N3. The positive trains of pulses have no effect on the source input pulses due to the presence of D1 which blocks the positive outputs from N2.

However, the negative pulses are allowed by D1 and these effectively sink the relevant sections of the basic source frequency, creating kind of rectangular notches in them at regular intervals depending upon the frequency of the oscillator set by VR1.

These notches or rather the rectangular pulses from N2 can be optimized as desired by adjusting VR1.

The above operation cuts the basic square wave from N1 into discrete narrow sections, lowering the average RMS of the waveforms. It is advised that the setting is done with the help of a RMS meter.

The output devices switch the relevant transformer windings in response to these dimensioned pulses and produce corresponding high voltage switched waveforms at the output winding.

The result is a voltage which is quite equivalent to a sine wave quality and is safe for operating all types of household electrical equipment.

The inverter power may be increased from 200 watts to 500 watts or as desired simply by adding more numbers of T1, T2, R5, R6 and T3, T4, R7, R8 in parallel over the relevant points.

Salient Features of the Inverter

The circuit is truly efficient and moreover it is a modified sine wave version which makes it outstanding in its own respect.

The circuit utilizes very ordinary, easy to procure types of components and is also very cheap to build.

The modifying process of the square waves into sine waves can be done by varying a single potentiometer or rather a preset, which makes the operations pretty simple.

The concept is very basic yet offers high power outputs which may be optimized as per ones own needs just by adding a few more number of output devices in parallel and by replacing the battery and the transformer with the relevant sizes.

Fully Transistor Based Modified Sinewave Inverter#4

A very interesting circuit of a modified sine wave inverter is discussed in this article which incorporates just ordinary transistors for the proposed implementations.

The use of transistors typically makes the circuit easier to understand and more friendly with the new electronic enthusiasts. The inclusion of a PWM control in the circuit makes the design very efficient and desirable as far as operations of sophisticated appliances are concerned at the inverter output.The circuit diagram shows how the entire circuit is laid down. We can clearly see that only transistors have been involved and yet the circuit can be made to produce well-dimensioned PWM controlled waveform for generating the required modified sinew waveforms or rather modified square waves to be more precise.

The whole concept may be understood by studying the circuit with the help of the following points:

Using Astable as the Oscillators

Basically we can witness two identical stages which are wired up in the standard astable multivibrator configuration.

Being astable in nature the configurations are specifically intended for generating free running pulses or square wave at their respective outputs.

However the upper AMV stage is positioned for generating the normal 50 Hz (or 60 Hz) square waves which are used for operating the transformer and for the required inverter actions, in order to get the desired AC mains power at the output.

Therefore there’s nothing too serious or interesting about the upper stage, typically it consists a central AMV stage consisting of T2, T3, next comes the driver stage consisting of the transistors T4, T5 and finally the receiving output stages consisting of the T1 and T6.

How the Output Stage Works

The output stage drives the transformer via the battery power for the desired inverter actions.

The above stage is only responsible for carrying out the generation of the square wave pulses that’s imperatively required for the intended normal inverting actions.

The PWM Chopper AMV Stage

The circuit at the lower half is the section which actually does the sine wave modifications by switching the upper AMV according to its PWM settings.

Precisely, the upper AMV stage’s pulse shape is controlled by the lower AMV circuit and it implements the square wave modification by chopping the basic square inverter square waves from the upper AMV into discrete sections.

The above chopping or dimensioning is executed and defined by the setting of the preset R12.

R12 is used for adjusting the mark space ratio of the pulses generated by the lower AMV.

According to these PWM pulses, the basic square wave from the upper AMV is chopped into sections and the average RMS value of the generated waveform is optimized as close as possible to a standard sine waveform.

fully transistor based PWM modified inverter

The remaining explanation regarding the circuit is pretty ordinary and may be done by following the standard practice that’s normally employed while building invertes, or for that matter, my other related article may be referred for acquiring the relevant information.

Parts List

R1, R8 = 15 Ohms, 10 WATTS,
R2, R7 = 330 OHMS, 1 WATT,
R3, R6, R9, R13, R14 = 470 OHMS ½ WATTS,
R4, R5 = 39K
R10, R11 = 10K,
R12 = 10K PRESET,
C1-----C4 = 0.33Uf,
D1, D2 =1N5402,
D3, D4 = 1N40007
T2, T3, T7, T8= 8050,
T9 = 8550
T5, T4 = TIP 127
T1, T6 = BDY29
TRANSFORMER = 12-0-12V, 20 AMP.

Design#5: Digital Modified Inverter Circuit

This 5th design of a classic modified inverter is yet another design developed by me, although it's a modified sine wave, it can also be referred as a digital sine wave inverter circuit.

The concept is again inspired from a mosfet based powerful audio amplifier design.

Looking at the main power amp design we can see that basically it's a 250 watt powerful audio amp, modified for an inverter application.

All the stages involved are actually for enabling a frequency response of 20 to 100kHz, though here we won't need such high degree of frequency response, I didn't eliminate any of the stages as it wouldn't do any harm to the circuit.

The first stage consisting of the BC556 transistors is the differential amplifier stage, next comes the well balanced driver stage consisting of the BD140/BD139 transistors and finally it's the output stage which is made up of the powerful mosfets.

The output from the mosfets are connected to a power transformer for the required inverter operations.

This completes the power amp stage, however this stage requires a well dimensioned input, rather a PWM input which would ultimately help to create the proposed digital sine wave inverter circuit design.

The Oscillator Stage

The next CIRCUIT DIAGRAM shows a simple oscillator stage which has been suitable optimized for providing adjustable PWM controlled outputs.

The IC 4017 becomes the main part of the circuit and generates square waves which very closely matches the RMS value of a standard AC signal.

However for precise adjustments, the output from the IC 4017 has been provided with discrete voltage adjustment level facility using a a few 1N4148 diodes.

One of the diodes at the output may be selected for reducing the amplitude of the output signal which would ultimately help in adjusting the RMS level of the transformer output.

The clock frequency which must be adjusted to 50Hz or 60Hz as per the requirements is generated by a single gate from the IC 4093.

P1 can be set for producing the above required frequency.

For getting a 48-0-48volts, use 4 nos. 24V/2AH batteries in series, as shown in the last figure.

Power Inverter Circuit

full bridge modified inverter using 2 batteries

Sine Wave Equivalent Oscillator Circuit

pwm processor

The figure below shows various waveforms outputs as per the selection of the number of diodes at the output of the oscillator stage, the waveforms may have different relevant RMS values, which must be carefully selected for feeding the power inverter circuit.

If you have any problems understanding the above circuits, please feel free to comment and inquire.

Modified Design#6 using only 3 IC 555

The following section discusses the 6th best modified sine wave inverter circuit with waveform images, confirming the credibility of the design. The concept was designed by me, the waveform being confirmed and submitted by Mr. Robin Peter.

The discussed concept was designed and presented in a few of my previously published posts: 300 watt sine wave inverter circuit, and 556 inverter circuit however since the waveform were not confirmed by me the relevant circuits weren't completely foolproof.Now it's been tested, and waveform verified by Mr. Robin Peter, the procedure revealed one hidden flaw in the design which has been hopefully sorted out here.

Let's go through the following email conversation between me and Mr. Robin Peter.

I built the simpler modified sine wave alternative version IC555's,with no transistor. I changed some of the values of the resistors and caps and did not use[D1 2v7,BC557,R3 470ohm]

I joined Pin2&7 of IC 4017 together to get the required waveform. IC1 produces the 200hz 90% duty cycle pulses(1 image), which clock IC2 (2-images) and therefore IC3(2 images, min duty cycle & max D/C)Are these the expected results, My concern is that it is a modified sine where you can vary the

RMS,not a pure sine



using IC 555 triangle wave for modified inverter

Hi Robin,
Your modified sine wave circuit diagram looks correct but the waveform isn't, I think we'll need to use a separate oscillator stage for clocking the 4017 with frequency fixed at 200Hz, and increase the frequency of the topmost 555 IC to many kHz, then check the waveform.Regards.

Hi Swagatam

I have attached a new circuit schematic with the changes you suggested along with the resultant wave forms.What do you think of the PWM waveform,the pulses don't seem to go all the way down to ground level.

using IC 555 modulated PWM

oscilloscope chopping waveform at mosfet gate

50HZ square waves

wide pwm adjustment

optimal RMS adjust

Hi Robin,

That's great, exactly what i was expecting, so it means a separate astable for the middle IC 555 must be employed for the intended results....by the way did you vary the RMS preset and check the waveforms, please do update by doing so.

So now it looks much better and you can go ahead with the inverter design by connecting the mosfets.

....it's not reaching the ground due to the diode 0.6V drop, I assume....Thanks very much

Actually a much easier circuit with similar results as above can be built as discussed in this post:https://homemade-circuits.com/2013/04/how-to-modify-square-wave-inverter-into.html

More Updates from Mr. Robin

Hi Swagatam

I varied the RMS preset and here are the attached waveforms.I would like to ask you what amplitude of triangle wave can you apply to pin 5,and how would you synchronise it so that when pin 2 or 7 go + the peak is in the middle

Here's some better modified sine waveform, maybe the guy's will understand them easier. It's up to you whether you publish them.

By the way i took a 10uf cap from pin2 to 10k resistor to .47uf cap to ground.And the triangular wave looked like this(attatched).Not too triangular,7v p-p.

I will investigate the 4047 option

sample triangle waves

Output Waveform across Transformer Mains Output (220V)The following images show the various waveform images taken from across the output mains winding of the transformer.

Courtesy - Robin Peter

No PWM, no Load

waveform showing when there's No PWM, no Load

No PWM, with load

waveform showing when there's No PWM, with Load attached

With PWM, without load

waveform showing when PWM is switched ON and no Load

With PWM, with load

waveform showing when PWM is switched and Load is connected

The above waveform images looked somewhat distorted and not quite like sinewaves.
Adding a 0.45uF/400V capacitor across the output drastically improved the results, as can be witnessed from the following images.

Without load, with PWM ON, capacitor 0.45uF/400v added

waveform showing with PWM ON, capacitor 0.45uF/400v added

With PWM, with load, this looks very much like an authentic modified sinewaveform.

with PWM ON, capacitor filter added and load connected

All the above verification and testing were conducted by Mr. Robin Peters.

More Reports from Mr. Robin

Ok,I did some more testing and experimenting last night and found that if I increase the batt voltage to 24v the sinewave did not distort when I increased the duty/cycle.( ok,I've regained my confidence)I added that 2200uf cap between c/tapp and ground but that made no difference to the output waveform.

I noticed a few things that were taking place,as I increased the D/C the trafo makes a noisy humming sound(as if a relay is vibrating back and forth very quickly),The IRFZ44N's get hot very quickly even with no loadWhen I remove the cap there seems to be less stress on the system.The humming noise is not so bad and the Z44n's don't get so hot.[of course no sinewave}

The cap is across the output of the trafo not in series with one leg. I took (3 different windings) round inductors{I think they are toriodal} out of a switch-mode power supply.The result was no improvement in the output wave(no change),

The trafo output voltage also dropped.

Adding an automatic load correction feature to the above modified sine wave inverter circuit idea:

inverter output filter circuit

The above shown simple ad-on circuit can be used for enabling automatic voltage correction of the inverter output.

The fed voltage across the bridge is rectified and applied to the base of the NPN transistor.
The preset is adjusted such that at no load the output voltage gets settled at the specified normal level.

To be more precise, initially the above preset should be kept at the ground level so that the transistor says switched OFF.

Next, the 10k RMS preset at pin#5 of the PWM 555 IC should be adjusted to generate around 300V at the transformer output.

Finally, the load correction 220K preset should be realigned to bring down the voltage to may be around 230V mark.

Done! Hopefully the above adjustments would be enough for setting up the circuit for the intended automatic load corrections.

The final design might look like this:

modified sine wave inverter with output filter circuit

Filter Circuit

The following filter circuit can be employed at the output of the above inveter for controlling Harmonics and for enhancing a cleaner sinewave output

inverter output LC filter circuit calculations

More Inputs:

The above design was studied and further improved by Mr Theofanakis, who is also an avid reader of this blog.

1200 watt modified inverter circuit

The oscilloscope trace depicts the modified waveform of the inverter across the 10k resistor connected at the mains output of the transformer.

oscilloscope trace for the 1200 watt modified circuit

The above modified inverter design by Theofanakis inverter was tested and approved by one of the avid followers of this blog, Mr. Odon. The following test images by Odon confirm the sinewave nature of the above inverter circuit.

Design#7: Heavy Duty 3Kva Modified Inverter Design

The below explained content investigates a 3kva sine wave inverter circuit prototype made by Mr. Marcelin using only BJTs instead of the conventional mosfets. The PWM control circuit was designed by me.

In one of my previous posts we discussed a 555 pure sine wave equivalent inverter circuit, which was collectively designed  by Mr.Marcelin and me.

How the Circuit was Built

In this design I have used strong cables to sustain the high currents, I used sections of 70 mm2, or more smaller sections in parallel. 3 KVA transformer is actually as solid weighs 35 kg. Dimensions and volume is not a drawback for me. Photos attached to the transformer and installation in progress.

The following assembly nearing completion, based on the 555 (SA 555) and CD 4017

On my first try, with mosfets, earlier this year, I used IRL 1404 which Vdss is 40 volts. In my opinion insufficient voltage. It would be better to use mosfets with a Vdss at least equal to or greater than 250 volts.

In this new installation, I foresee two diodes on the transformer windings.

There will also be a fan for cooling.

TIP 35 will be mounted by 10 in each branch, like this:

how to TIP35 BJTs in a 3kva inverter

Complete Prototype Images

3kva modified sinewave inverter prototype image

3kva transformer image

3kva modified transformer wiring image

Finalized 3 KVA Inverter Circuit

The final circuit design of the 3 kva modified sine wave inverter should look like this:

3000 watt inverter modified full circuit diagram

How to Safeguard the Transistors

Note: In order to safeguard the transistors from a thermal runaway, mount the individual channels over common heatsinks, meaning use a long single finned heatsink for the upper transistor array, and another similar single common heatsink for the lower transistor array.

Mica isolation would be fortunately not required since the collectors are joined together, and the body being the collector would get effectively connected through the heatsink itself. This would actually save a lot of hard work.

In order to obtain maximum power efficiency, the following output stage is recommended by me, and must be employed with the above explained PWM and 4017 stages.

Circuit Diagram

configuring 3kva output power stage using TIP36 and TI122 BJTs

Note: Mount all the upper TIP36 over a larger finned common heatsink, DO NOT use mica isolator while implementing this.

The same must be done with the lower TIP36 arrays.

But make sure these two heatsinks never touch each other.

The TIP142 transistors must be mounted on separate individual large finned hearsinks.

Need Help? Please send your queries through Comments for quick replies! And please Bookmark my site :)


Swagatam said…
One 50Hz cycle consists of 50 alternate positive and negative peak voltages.
The above pulses are normally in the form of square waves.
The PWMs simply chop the above 50 square waves into thin sections, this results in removing or cutting off some magnitude of the total value of the voltage involved in the original 50 square wave pulses.
We do this to pull down and match the RMS of the pulses with a standard sine pulse.

THe mosfet gate receive the above voltage and switch the battery voltage exactly in the same pattern across the trafo winding through it drain/source leads.
Swagatam said…
The PWM has no connection with 50Hz switching frequency.
50Hz cycless are created by the alternate switching of the 4017 IC.The PWM are used to break each pulse of the 50Hz cyce into thin calculated sections for setting up the RMS in accordance with a standard sine pulse.
Here the PWM does not depend or need the exact replication of a sine wave, therefore a sine wave input was not felt necessary
alex said…
hello Mr Swagatam so this is the wave form u need to feed into the transformer output to produce the desired sine wave output u designed for. Thanks for ur support
Swagatam said…
hello alex,

yes that's right,

let's thank Mr. Robin for correcting and confirming the facts....
Swagatam said…
the voltage drop is because of load wattage exceeding the specified normal rating of the inverter (battery power), it's not because of the fets drawing more current, fets only act like switches, they have nothing to do with load current.
No inverter can compensate or increase the output voltage if the load exceeds the maximum allowable capacity, because battery is the ultimate power source beyond which the inverer cannot get anything.
Swagatam said…
to an extent it may be true, but the above design will also include harmonics(high frequency harmonics) which might cause some noise, although much reduced than an ordinary square wave inverter, it can be removed by additional inductor/capacitor network at the output of the trafo.
Swagatam said…
pin2 and 7 both will ofcourse produce positive voltages, 50 times each.
the connected mosfets will also conduct accordingly 50 times each but alternately, meaning one after the other and never together, creating 100 alternate positive pulses across the transformer winding.
However the trafo winding polarity being opposite for the two mosfets, the conduction inside the two half winding create positive and negative push pull induction inside the core.
This neg/positive induction gets stepped-up to become positive and negative 50 Hz cycles across the output winding.

so it's the trafo which is responsible for switching the alternate positive pulses from the mosfets into alternate positive and negative AC.
alex said…
hello Mr Swagatam we all thank mr Robin for his great efforts we anxiously the rest of the project. Would we still use the rest of the circuit that deals with the voltage correction using the bridge rectifier and transistor config. Thank u
Swagatam said…
thanks! yes you are right, I'll do some research on it and try to put up a related post in this blog soon,

555/4017 = 10mA
4047 = 5mA

it doesn't really matter because mAs won't even scratch the battery anyway.
Swagatam said…
Hello Alex,

Voltage correction can be included, depends on the user! However it can be done through an opto coupler stage as discussed in one of my previous posts.
alex said…
ok mr Swagatam so as soon as he completes his test we would appreciate u to redraw the schematic and give us the final circuit because now we would not know what are the different pot for and how to adjust what u would not know how much of us await ur support keep the good work going sir
alex said…
yes Mr Swagatam I see where uused the optp coupler in the revised version of the inverter but I am not too clear on this because in a post dated August 23 I see where u said this wont help with varing loads please help us here . on this valid point in an inverter. Thank u
Swagatam said…
there's a way by using the reset pin#4 of the PWM IC555 as the shut down input.

A sample voltage is derived from the trafo output via a high value preset or voltage divider network and fed to th base of a NPN transistor.
The transistor collector is connected with pin4 of the PWM 555, while the pin4 in turn connected to positive via a 10k resistor.

he preset is adjusted such tat at around 250V, the transistor just begins to conduct. thereby pulling down the reset pin#4 to ground and shutting off the PWMs,

This goes on continuously making sure the output never exceeds the 250V mark.
Swagatam said…
surely Mr.Alex...thanks very much, will keep you updated!
Swagatam said…
I probably said that it won't increase the voltage if load increased above the battery max limits, but otherwise the opto coupler method will certainly do the corrections as per expectation,
anyway i'll try to update the method discussed in the previous comment soon here.
Swagatam said…
Hi Marcelin, welcome back.

For making a 3kv system, I am afraid you would have to take care of a few tings, first of all you will have to employ and not transistors, and most importantly a supply voltage more than 50V, actually the higher the better. Also an H-bridge is strictly recommended for such designs, I'll be soon posting a comprehensive design on this soon.

Swagatam said…
..I meant mosfets and not transistors....
Swagatam said…
the central 555 which has a 10k preset at its pin5
Swagatam said…
Go ahead with your feelings and get past your boredom:)... the above design has been proved beyond doubt by Mr. Robin and me, so I think there's hardy any chance that you would fail....moreover we are all eager to see a working prototype of this from somebody.

I'll try to update the required load correction feature here soon.
Swagatam said…
Actually we could also try connecting the BC547 collector with pin#5 of the PWM IC, as soon as BC547 begins conducting it would tend to bring pin#5 potential towards zero which in turn would result in wide spaces in the output PWMs making the mosfets slower with their conduction.
With mosfets conducting lesser would mean lowering the output voltage and vice versa.

BC547 is NPN, ..........PNP will not work
alex said…
Thank you we await your reply on this because I want to know what gets adjusted when output voltage falls to do the compensating if it is the sine wave pulse width or what. Thank u
alex said…
Hello Mr swagatam have u heard from Mr Robin we need to know how this project work out. I can tell u Hundreds of hobbyist are waiting on ur result because the circuit has been rearranged so many times we really want u to give us a finish circuit with voltage correction circuit included . thank u sir
Swagatam said…
Hi Marcelin,

With 12V, trying to run a 3KVA inverter would call for hugely thick wires and a massive transformer....everything could get too bulky....and TIP35 is rated at just 25Amps, many of them would be required to cater for the massive 200amps requirement of the design.

Anyway it would be interesting to see how you manage them at your side
You can send me the images to my email ID hitman2008@live.in
Swagatam said…
I have updated the above article with the required info...pls check it out.
Swagatam said…
Hello Alex,

Yes, Mr. Robin has answered positively he would soon build the final design and inform us, let's wait for the results...from my side I can assure you that the above design would definitely work...
alex said…
Mr Swagatam I see u have updatedthe final drawing and also the voltage correction circuit. we alll appreciate ur support What is the perpose of the 2k pot on the left 555 is it to set the frequency to 2khz. Is the second 555 running at 2khz also. Please tell us the purpose of the 10k pot on the bottom 555 ic. Could u give us a clearer drawing we cannot see the values of some of the components Sir. We are thankful to u sir. I am starting to collect the parts right now sir
alex said…
Hello Mr Swagatam should we use a small transformer accross the output transformer of say about 12v or so to connect to the bridge rectifiers or connect it straight accross the 220ac volts. Thank u
Swagatam said…
Hello Mr Alex,

yes the left side 555 control is for adjusting the PWM pulse frequency (thin chopped pillars in the waveform).
The bottom 555 10k control is for adjusting the frequency of the trafo output (50 or 60Hz). The parts are not very critical, slight variation will not matter.

The load correction bridge should be directly connected to the mains output and not thru any additional trafo.
alex said…
Thank u Mr Swagatam for explaining. So what frequency should we be getting at pin 3 of the left 555 and pin 3 of the middle 555 thank u Sir
Swagatam said…
2kHz from the left 555, not sure what would be at the output of the middle 555 output because it would be produced after comparing with the triangle waves at the collector of PNP transistor BC557
alex said…
thank you Mr Swagatam for ur answer but I am not sure about that transitor u are talking about because i dont see no transistor in the circuit away fro the npn bc457 that is used for the voltage correction only the 4 ic please check I am looking at the circuit above which states ( the final desing might look like this) awaiting ur reply Sir
Swagatam said…
Hello Alex,

I just missed it, actually Mr.Robin did not use the transistor which existed in the original design at pin6/7 of the middle 555 IC. So as mentioned in the earlier comment here the triangle waves are taken and compared at pin6/7 of the middle 555 IC.
alex said…
ok Mr Swagatam which circuit should I follow the original design or the last design that Mr Robin has drawn above because I am ready to build the circuit now and tell everyone the results
Swagatam said…
You can follow the above circuits, designed by Mr. Robin.
Swagatam said…
The triangle waves are generated by the 555 itself at its pin6/7, so you dont have to feed it externally.

Configure the 555 in a monostable mode....feed a high frequency SQUARE WAVE at its pin2 and sine wave from the bubba at its pin5 ....and now check the result at pin3.
joel said…
hello mr swagatam could u refer me to any of ur pure sine wave inverter circuits that have been build and tested by any reader because I want to build a working one and try to understand this wave form theory Sir. Thank u and keep up the good work
Swagatam said…
hello Mr Joel, you can try the above shown design, as you can see the waveforms are verified and they look exactly as assumed by me for the design.
joel said…
thank u I will try it .so that wave form is the wave form before it drives the fet so how would we get a sine wave at the secondary of the transformer. Thank u
Swagatam said…
The calculations are rather simple:

Remember, there's a gap between pin2 and pin7, and also before pin in the 4017 output sequence, which is reducing the duty cycle to 25%.
we can make it to 50% by using pin3, pin2 as the outputs for driving the mosfets, and connect pin4 with pin15 for resetting.
The PWM will obviously reduce the duty cycle by 50%.

That's why I have always recommended using a transformer with input rating 50% less than the batytery voltage, meaning if the battery voltage is 12V, then the trafo must be rated with 6-0-6V input.

The above corrections will solve all the issues suggested by you and present the desired ideal design
Swagatam said…
According to me the harmonics can be controlled by adding a simple L/C network across the center tap and ground of the transformer...however I am not sure what values would be appropriate, it could be found by a little trial and error.

An example image can be seen here:

Chandrajith.P said…
Hello Sir,
Question regarding "How to Calculate and Match an Inverter Circuit with Battery and Transformer"
If I use 12v battery,
Max load I need is 25w,
Transformer output = 62.5w,
Transformer current = 62.5/12 = 5.2083A => Used 5A
Battery current = (5.2083/4)+5 = 1.302075+5 = 6.3A => Used 10A,
Now my question is,
What is the maximum backup time in hour(if maximum load connected is 25w)?

Swagatam said…
Hello Chandrajith,

I have replied this question in your previous comment.
Swagatam said…
fets will drive the trafo exactly as per the input gate waveform, the waveforms as explained in the above article are optimized sine equivalents which can be verified across the trafo mains output
Swagatam said…
If you are not comfortable with 6-0-6 tafo then you can increase the battery voltage to 24V and use a 12-0-12 trafo....will give you the same results.

as discussed in the previous comment, use pin3 and pin2 as the outputs from IC4017, and connect only pin4 with pin15 for resetting the IC back to pin3...this will give you 50% duty across cycle at the relevant pinouts.
Theofanakis Kostas said…
Hir Sir
I built it with 4017 and I realize that every 1/4 of the 50Hz cycle I have both +,- at this time instead of only + pulses and in the other 1/4 of the 50Hz the - pulses of the modified sine wave. How do you cut the - pulses in the first 25% and the + in the next 25%?
alex said…
hello Mr Swagatam with regards to your filter and the link that u refer to on the 3rd Nov 2013 how would this filter be conected from center of transformer to ground because the drawing shows in and out. Dont know if its the right link I saw.. There is a coil in series and a cap accross. Please helpmus here Sir. Thank u
Swagatam said…
Hi Theofanakis,

The mosfets are responding only for (+) signals from the 4017, and have no connection with (-) signals.

It's the transformer that is responsible for inverting the mosfet signals into (+)/(-), alternately.
Swagatam said…
One end of coil to transformer center tap, other to battery positive, capacitor free bottom end to ground.
Theofanakis Konstantinos said…
Hi again
I want to sent you some changes that I made in order to solve the gap between positive part and negative part of the sine wave. I also have a picture of the final modified sine wave with resistor load. Would you might tell the way that I could publish it here?
Thank you
Swagatam said…
Hi Theofanakis,

Thank you very much, I'll update the info in the above article soon.

By the way could be please briefly explain why and how the use of 4066 ICs help the above circuit? I would love to update the info here for the benefit of the readers.

Swagatam said…
At the gates of the mosfets, the pulses are all (+) or zero, there's nothing called (-) pulses.

+/- waveform is created by the transformer since its primary is subjected with a push-pull effect across the mosfets drains which generates the required (+)(-) waveform at the output mains.
Theofanakis Konstantinos said…
The IC3 produce 100Hz and the 4017 divide it at 50HZ. The pin2 controls which switch will be on so which mosfet will output the pwm signals produced by the IC1,2. That's the reason that I don't have gap between positive and negative signal at the transformer's output.
alex said…
hello Mr Swagatam could u show us a drawing of how to connect the filter u recommend at the output of the transformer thank u Sir and have u hear from Mr Robin yet about the final stage
Swagatam said…
Alex, it's very simple, connect one end of the coil to battery positive and the other end to transformer center tap, that means the battery voltage has to pass through the coil for entering the trafo center tap.

Next connect one end of the capacitor at the center tap of the trafo and the other end to the negative of the battery
Swagatam said…
Thanks for the valuable inputs Robin,

Those figures look reasonable and valid.

By the way could you please show us the waveform as received at the mains output of the transformer? This is something that every one wants to look at.

And also please tell us about the input rating of your trafo in terms of voltage and current.

Swagatam said…
Yes, a gap between the mosfet gate triggering may be suitable for the above design as it will tend to make the output go down further.
Swagatam said…
...i meant a gap may NOT be suitable
alex said…
Thank u Mr Swagatam for the connection of the filter and we are all so glad to hear from mr Robins just want him to show us the wave form to verify a sine wave output thank u for your support
alex said…
Mr Swagatam I should ask u if that coil is air core or ferrite core and about what value just an estimate in what range should we start with thank u
Swagatam said…
Mr Alex, it will require a ferrite torroidal core. You can try with 5 turns of 1mm thick copper wire. The capacitor can be a 1uF/50V nonpolar.
Swagatam said…
Hi Robin,

Making mistakes is a part of the game.
Ideally the trafo voltage should be less than the battery voltage, this will allow generating optimum voltage levels at the output, since a PWM optimizer is involved here.
Yes the load will tend to make the PWM oscillate a bit due to the feedback up/down effect, if a cap settles it, no issues we can go for it.

keep us updated, appreciate it.
Swagatam said…
it's a lengthy theory, cannot be explained in short here.
Swagatam said…
The extra ICs are not required, we just need to use pin3,2 with the mosfet gates and connect pin15 with pin4 of the IC 4017
Swagatam said…
multiplying the number of outputs with 50Hz we get 50x2 that's equal to 100, so now the input frequency will need to be 100Hz.
Swagatam said…
Thanks for the suggestion, it could be true but needs to be confirmed through practical verification.

Another rectification could be to use pin3 and pin2 of the IC 4017 as the outputs and connect pin4 with pin15, and feed a 100Hz to its pin14.... this will remove the gap between the wave cycles and produce continuously varying AC cycles.
Swagatam said…
Thanks very much Michael for this comprehensive update...I appreciate it.

I think it's always a better and technically correct to rig the active ICs itself for implementing the voltage regulation of the output, because every IC invariably has some kind of input which can be optimized for controlling and influencing the output, for example in the above circuit as pin#5 potential of the PWM IC is shifted toward zero, the output also proportionately comes down toward zero....and this does not heat up anything.

So I think as discussed in the above article we should use pin#5 of the IC for the enforcing the output regulation control instead of the mosfet gates.

thanks, keep updating your thoughts.
alex said…
hello Mr Swagatam I am pleased with the good results u are having with this very important circuit. I am trying to build it but I am having some problems dont know if it is because I am building it in stages. I have just built the section with the 4017 fets and transformer and the 555 which is producing the 200hz. what is happening is that I am getting ac output but the fets are running very hot few seconds and I loose them. Dont know what is the problem i am getting about 3.8v on the output of pin 2 and 7 at 50hz. I think the circuit should work alone by itself please help me here sir. Thank u
Swagatam said…
yes you are correct, the feature will automatically adjust the output voltage and try to keep it near the optimal level with varying loads, but only as long as the load is well within the limits of the inverter maximum deliverable power capacity.

I think an optocoupler would provide a better bidirectional optimization than a transistor as shown in the last diagram on this page:


Swagatam said…
Hello Alex,

Replace the 4017 section with 4047 IC circuit as shown below and then check the response, the issue might be due to lack of dead time from IC 4017 or absence of drain source diode across the fets.

alex said…
thank u Mr Swagatam for ur support . The fets I am using are ifrz44 which have diodes accross the drain to source junction. which components would I change to alter dead time on the 4017. I still want to try with this 4017 in that the other guys have built it and are working Sir. I await ur reply
Swagatam said…
Alex, the circuit discussed in the above article has employed dead time by skipping pin#3 and pin#4 across the 4017 outputs, so this is the way it needs to be done.
Swagatam said…
Thanks Michael, that's good bit of info, I hope this will help Mr. Alex to troubleshoot his circuit.
alex said…
Hello Mr Swagatam and Micheal I am glad to tell u that the problem as just stoped the fets are not running hot again thank u for the encouragement. I also built the rest of the circuit when i connect the diodes to the gates the voltage drops by about half well that i think can be corrected. What happens now is I am getting the 2khz frequency at the output of the transformer I think we are getting somewhere now. Could u explain how the middle 555 ic works and how to adjust the 10k pot what results should we check for I am following the above circuit of Mr robins as u said I should do. Should there be a cap from pin 5 of this same ic to ground I await your reply . Thank u Sir
Swagatam said…
Hello Alex,that's great news.....please remember that without the PWM diodes connected to the mosfet gates the output should reach around 500V....are you getting this much voltage at the output?

And i have clarified this many times that the trafo input rating must be 50% less than that of the battery voltage....example 6-0-6 for 12V batt.
Swagatam said…
a cap at pin5 is not critical
Swagatam said…
Yes, forcing a higher voltage into the low voltage winding will force equivalent higher voltage across the output winding than the actual rating.

we are not interested to run the trafo at this forced voltage as it will heat up the trafo, it's here where the PWM comes into play for adjusting the output to the optimal 220V level.
Swagatam said…
it will display the average voltage for the negative and positive half cycles, irrespective of AC or DC, so it's fine to use it according to me.
Swagatam said…
yes, he got over 500V with a 12-0-12V trafo using a 26V batt
alex said…
hello Mr Swagatam thank u for your usual support to us . I know that the transformer should be about 6-0-6 for 12v supply but my transformer is just 10-0-10 the voltage is not a problem to me now because I know the transformer ratio. What I wanted u to do was to explain what is the purpose of the middle 555 and the use of the 10k at pin 5. The other problem with me getting 2khz at the output of the transformer is this a case that I need a filter now to get rid of the 2khz frequency now so as to see the 50hz usable frequency. This is where I need u to clarify for us and we appreciate ur support to us all. Thank u sir and I await ur answer
Swagatam said…
hello Alex, you can go through the following for understanding the role of the mentioned 555 IC and the 10K preset:


The 2khz is the PWM for optimizing the RMS only, and will not change the 50Hz cycleit will only chop the individual pulses of the 50Hz....so the output frequency will remain = 50Hz.
alex said…
thank u Mr Swagatam I read the blog and now i understand the function u made it so simple . So the 10k would be to adjust the pulse width at the gates of the fet. so I think this will adjust the output voltage at the secondary of the transformer Sir. please correct me if I am wrong.With regards to the 2khz what i am saying is at the output of the transformer when I connect the diodes the frequency changes to 2khz instead of 50hz so I wanted to know what was wrong here because u said I should still be getting 50hz only chopped at smaller pieces please help me here sir thank you
alex said…
hello Mr Swagatam today i made a change on the circuit i put a 2.2uf cap accross the transformer out and I got back the 50hz when I check before it was actually giving me about 1089khz at the AC volts out but with the cap i am getting a difference. Dont know if this is a right approach.another thing I should youI notice when i connect the diodes is I see the gate voltage falling from about 4v to .08 is this normal. well reaching so far i dont know what kind of waveform i am getting now because I dont have a scope. Any other word from Mr Robin or Miacael about their progress. I await ur usual support Sir
Swagatam said…
In systems that have no load correction, the maximum voltage is set for the optimal level (example 220V), means from here the voltage will only go down when its loaded, it can stay stable but surely cannot rise at any cost.
whereas in our system, the max voltage is set for 400V or more and is optimized at 220V according to the load conditions by the correction circuitry, in the above example it's done by automatically adjusting the voltage at pin#5 of the relevant 555 IC.
Swagatam said…
Hello Alex, the 4017 output is responsible for triggering the mosfets with the intended 50 Hz frequency...one mosfet turned ON 50 times per second to produce the upper half cycle....the same for the other mosfet which creates the lower half cyces 50 times per second.

If your 4017 IC gets the required 100Hz pulse at its pin#14 hen this function will execute correctly and the output will show 50Hz.

When the diodes are introduced at the gates of the msfets, the PWMs cut the above 50Hz cycles at the mosfets gates into fine segments such that the average output RMS gets optimized at the rated voltage (220V here). this is controlled by Increasing or decreasing the space ratio of the PWMs.
I hope this clears your doubts...

the waveform shown by Mr Robin Peter above operations distinctly evident.
alex said…
Hello Mr Swagatam thank u Sir I understand your explanation quite well about the pwm chopping up the wave form into smaller sections . The thing I am asking u is if it is normal for the gate voltage to drop from about 4v down to .08v when pwm is applied to the gates this is what i need u to answer Sir . Thank u. I think this is one of ur busy blogs because it is very informative and looks promising. I await ur reply
Swagatam said…
1) step down trafo is not required because current is immaterial here.
2) a filter cap can be added at the base/ground of the transistor for better response
Swagatam said…
the gate voltage will depend on the space width of the PWM, if you have increased it to an extent which corresponds to zero voltage then the gate voltage would also drop to zero....adjust the 10k preset toward the positive for reducing the space width and for increasing the gate voltage.
Swagatam said…
yes, it can be tried. but RC will not do...you can try only with a high value Cap...may be 2200uF across center tap and ground.
Swagatam said…
yes pwm may give rise to heat in the trafo, so better to first filter out the high frequency content and carve the waveform into a decent looking sine equivalent, it could be done using a LC filter, not an RC.
Swagatam said…
inductor won't help the cause according to the latest reports from Mr. Robin.
alex said…
hello Mr Swagatam I did not get to do more testing because i raise the voltage to 24v and imidiatly the output fet burst into flames so I have to go and try again. At 12v it was ok. Mr Robin is having quite similar heating so please help us here Sir. Thank u
Swagatam said…
hello Alex,
it could have burnt due to excessive current....increasing voltage increases current too....you should have increased the voltage by keeping the PWM to lowest point.
Swagatam said…
I have updated the latests from Mr. Robin.
Swagatam said…
1) keep the 10k preset toward the ground and make sure the PWM output the IC shows near 0V in the voltmeter.
2) wider pwm blocks will force the mosfet to conduct more which in turn will allow more votlage/current into the trafo
Swagatam said…
250V or 280V trafos could be difficult to get in the market.
alex said…
Thank u Mr Swagatam for ur reply I will try to do the adjustment and try again because we are determin to get it to work. We all appreciate the work that Mr Robin Maechaeil Majumdar and many others are doing to make it a success.As soon as I get more fets I will power up again Sir and let u know the results
alex said…
Hello Mr Swagatam I am up again with the inverter and ready to test again. without pwm i am getting very high volts which is normal with the pwm diodes connected i get 104v but as I said before the gate voltage falls I adjust pot 10k to the positive as u said above in a post but this only brings it up to about .9v and the output frequency at the transformer is about 1khz and not 50hz as it was before without pwm. I am designing 120v system please help us here Sir
Swagatam said…
the PWM output should show a voltage between minimum 0 and max near to 2/3rd supply volts when the 10k preset is varied from ground to positive.

If this is not happening means your PWM circuit is not working or is faulty.

remove the pwm and then check the output freq, if it reads 50hz would mean your circuit is correct and the 1kHz after pwm connection is simply a misinterpretation or inability of your meter.

Actually a scope is strictly recommended for such projects.
Swagatam said…
Michael, the PWMs will not influence the count of the blocks rather the thickness of the blocks, meaning with 10k slider shifted toward ground will decrease the thickness of the blocks and vice versa keeping the number of blocks always the same.
The above will read in the form of proportionately varying voltage when measured with a voltmeter.
Swagatam said…
....hence the name pulse width modulation
alex said…
thank you Michaei I am using pin 2 and 7 as output now so I await the result of the questiond between u and MR Swagatam to continue because that is my problem now with the voltage being low when I connect the pwm, Thank u
Swagatam said…
Thanks Michael,

Useful update, thanks very much...the fets will start becoming hot once you use the actual power trafo with optimum load at the output.

Anyway i think you have a wonderful job without involving the 555ICs and only with opamps.
alex said…
ok Mr Swagatam and Michael I have seen your great discoverys and success so what do i do now to move from where I am stuck. Congratulations Michael it seems u are well on your way to the final product great I await ur reply
Swagatam said…
3524 will never produce pure sine wave PWMs, unless treated with external circuits as done above.
The circuit discussed above is a full fledged pure sine wave equivalent inverter circuit,,,, the external capacitor is only helping to the carve out the harmonics and to shape up the modified pure sine waves into conventional pure sine wave that we are more familiar with.
alex said…
thank u my friend if u look in the post n dec 3 I have written again thank u for ur help
Swagatam said…
Hello Michael, I have just tried to introduce the concept of optimizing a flat square wave into a modified sine wave. We say modified sine because we optimize and match it's RMS with an conventional sine wave RMS.
The IC 555 becomes the simplest and the cheapest option for implementing this and that's exactly what I have tried to explained in the above and in many of my previous articles.
The harmonics are the only issue here which can be taken care of by employing suitable L/C filters at the output of the trafo.
We should keep the chopping blocks to some lower number, may be to 3 or 4 this will prevent the trafo from getting hot.
Alternatively we could go for ferrite trafos and increase the number of PWM blocks to as many numbers as possible and check the results.

The PWM blocks can be tweaked by increasing or decreasing the input frequency.
Swagatam said…
I don't think the number of blocks have anything to do with the quality of the sine wave, it's the RMS optimization and harmonic filtration that are connected with sine wave performance.
ferrite material can handle high frequencies with great efficiency without generating heat, whereas iron stamping are specified for lower frequencies only, that's why i doubt that higher PWMs could reduce the efficiency of the inverer if an iron core trafo is used.
Swagatam said…
yes LC filters are always recommended for such applications....so it could be the right approach.

voltage drop is one big drawback in such arrangements, you may refer to the following example and see how an LC filter is employed at the outputs of this simple square wave inverter circuit:

alex said…
I still await ur help to move on and make this project be a success
Swagatam said…
yes the trafo will have a ferrite core, however now the dimension will become too small compared to the iron core trafo.........wires will be always copper wires.

here's one example of a compact ferrite cored inverer, although here the application is intended as a CDI unit, the concept is of an inverter:

alex said…
Hello Michael I am so sorry I did not see your reply I though u had forgotten me. This is so help full now I know someone else has the same problem with the 1khz frequency at the output like I have and a cap accross has corrected it. I will try pin 2 and 3 but should we still connect pin 10 to pin 15. I really thank u foor telling me about the visual analyser. I will do the changes and post it here so everyone can know the progress. Happy too know of your sucess with yours so have u built the voltage correction section as yet to see how well it works because this is crusial in an inverter. we really thank Mr Swagatam for helping us. Looking forwart to hear from u.
Swagatam said…
ferrite transformers are always smaller and much efficient than iron core counterparts. however their calculations could be entirely from the iron core types so first you will need to find out the exact dimensions, turns, thickness etc for getting the right trafo with the right specs.
Swagatam said…
Hello Michael,

You can take the help of the following circuit which is actually a CDI circuit, however it can be referred to as a classic mini Ferrite core inverter.

Swagatam said…
The cdi circuit gives an idea regarding making a basic inverter ferrite trafo which can be studied and modified further through trial and error, however taking a professional help could be even better.

yes the formula would hold good even for a ferrite trafo.
Swagatam said…
The frequency will influence the voltage so I think you cannot change the frequency once it has been decided in the design.
alex said…
hello Mr Swagatam I am putting together a proble to use on the pc scope Mr Michaeil recomended so I will be able to give u a better report on the project. Thank u for ur help to us
alex said…
Hello Michael I tested the analyser today but dont know if its something with my probe or thats so it works. When i plug a small transformer into my house power outlet The wave form I get well somewhat looks like a sine wave its clean but some of the lines are croocked not straight is it that way urs show not able to post it here that others can see because not sure how to view the format it is saved in just want to clear this up but it works Thank u
alex said…
thank u for ur caution yes I have like a 1meg in series with the signal line of the probe now I know u have similar wave form so tomorrow I will test it on the inverter and see the response and post it here because this is one of the most important circuits online and hard to find.
Hello, do u have any inverter design using feritte transformers?
Swagatam said…
you can the try the design given in this article:

Hello swgatam, I got an idea. Can we set our 555IC to 200Hz, 25% duty cycle to make the wave resemble a PWM?
Swagatam said…
Hi ifeanyi, yes it can be done, the circuit has a wide option one can play with.
Hello swagatam, I use 2pairs of IRF3205 mosfet, how can I connect the PWM accross the 4 mosfet gate.
alex said…
hello Mr Swagatam I am sort of busy at the moment so I am not able to do any more test on the circuit. Have u got any more update from Mr Robins or Michael on their side . As soon as I can I will post a report
Swagatam said…
use separate resistors on each gate of the mosfets, and connect separate diodes on each gate, then terminate the common diode cathodes with the PWM source
Swagatam said…
Alex, no further updates received, however the situation looks quite convincing now and there's hardly any doubt regarding the circuit except the issue of using a ferrite cored trafo
mexzony said…
Sir should an electrolytic capaicitor be put at the output or a non electrolytic capaitor.
i noticed that when i put an electrolytic capacitor at the output it gets hot quickly.
Arun Dev said…
Sir could you please suggest three modifications in this circuit as said below
1). to suppress the noise produced by the transfomer due to high harmonics
2). An automatic overload protector
3). Low battery cut off feature
Swagatam said…
It should be a non-polar strictly....use a metallized polyester capacitor for perfect results.
Swagatam said…
Arun, I would suggest that you should first complete the basic circuit of an inverter having 100 watt output, once you succeed then we can proceed with the other additional features.
Robin said…
Hi Swagatam
I would like to wish everybody a prosperous and happy new year,I really have been following the progress on these inverters and if I can help in any way I will,be assured,up untill now I realize I"ve got a lot of studying to do,With the guidance and expertise of our friend Swagatam I'm sure we can achieve what we want
Best wishes to everyone
Swagatam said…
Hi Robin,

Wish you too a merry Christmas and a Happy New Year from all here.
We all very much appreciate your valuable inputs to this blog and will keep cooperating with you whenever you need us.
Thanks and best wishes.
thanks for the waveforms..
mexzony said…
hello sir,
is it recommended to use a non polarized capacitor at the output of a inverter when filtering.
i noticed that when i used a polarized 2.2uf/400v cap at the output it blew after some seconds and brought out some sprayed some liquid especially whem i used a 15-0-15/220V trafo that was used in a 1kVA inverter.The capacitor just could not withstand it..i then looked at schematics for capacitors placed at the output of inverters and notice that they are usually non polarized.
Why does polarised cause issues lihe this?
Swagatam said…
Helo Michael,

the output from an inverter is always an alternating voltage consisting of alternating positive and negative cycles, so a polarized cap will never work in such conditions, therefore a nonpolar cap is only recomended.
mexzony said…
hello Sir,
i decided to discard using a sinusoidal pwm because of the fact that i was not getting constant voltage after connecting the PWM diodes as this made the output voltage fluctuate a lot.At first i thought it was because of the high frequency hitting my digital meter but no it was not so.
Any way here are my adjustments
1)triangle wave using opamp compared with DC voltage using a 10k slider just like yours at more than 16Khz and when applying PWM diodes gate of FETs the voltage was stable.
2)As i increased the voltage using the 10k slider up to nearly maximum supply voltage the width of the pulses reduced causing reduction in output voltage and Vice versa.
3)i had to amplify the triangle wave signal so that its peak to peak voltage is very high about 11Vp-p as this will mean that with even the slightest adjustment of the 10k slider up or down i get PWM signal,the only thing is how wide the width will be but a good PWM signal.
This amplification will play a crucial role in the voltage correction circuit.
Now to the voltage correction circuitry,
Sir like i suspected the BC557 NPN configuration did not work at all as i tested it and instead of adjusting voltage it pulled the voltage down to 0V no matter how i tried adjusting both the both preset it did not work and eventually the transistor burned along with the 10k preset when trying to adjust them giving me a painful jolt on my fingers.
mexzony said…
Now i used a BC557 PNP configured in the common collector or emitter follower and it worked in controlling the voltage after the initial voltage had been set using the 10k preset to give us a high voltage at the output.
but here is how it should be done.
on a side note i used a step down trafo 9-0-9/300ma/220V as feedback as i am not comfortable feeding 220V directly to the rectifier diodes.
1)after the whole set up has been wired both the 10k preset and the 220k preset should be at Ground or 0V.
2) remembering that the amplitide of the triangle waves have to be very high for effectiveness and also the fact that as i increase the voltage using the 10k preset the width decreases and as i lower the voltage the width increases this means that for low DC voltage into the comparator the PWM pulses would be longer and result in high AC voltage at the output and this is due to the fact the the triangle is very high in ampltude.
3)As i said after wiring up every thing with both preset set to Ground or 0V,
we then put on the inverter and then we wont get AC voltage at the output yet so we now slowly begin to adjust the 10k preset just until it just begins to conduct and i siad slowly because the 10k preset will get hot if we fully adjusted it especially now that it has been connected to a transistor so that changes how it works now.
Now once it begins to conduct we should have PWM with AC voltage very high using appropriate trafos and the DC voltage gotten by adjusting the 10k preset should be about 1.5VDC-2VDC max resulting in wider pulse width and high AC voltage.
Now as this AC voltage is fed back through the feedback trafo we begin to adjust the voltage correction preset such that as we increase the voltage at the base of the PNP transistor, the DC voltage which is being compared to the triangle wave increases and this results in reduction of the width of the pulses as DC voltage increases ultimately correcting the output AC voltage to the desired 220VAC or 230VAC we want.
So now the voltage correction preset long with the transistor is now responsible for ultimately correcting the output voltage automatically as the required voltage level info is fed to the base of the transistor and this in turn corrects the input DC voltage which adjusts the width of the pulses to give our desired output AC.
Hope everyone understands.
if anything comes up i will post
Swagatam said…
OK got it, thanks however the transistor protection circuit will surely work provided the potential divider is set correctly. It's only a rough concept that I have provided, it will some tweaking until perfection. And yes the 10k preset PWM at the relevant pin#5 should be applied through a 0.22uF or a suitable low value capacitor so that it doesn't load the transistor and burn it.
Swagatam said…
..it's BC547, not BC557.
Swagatam said…
That's great, thanks Micheal, I hope this version helps the readers to get an alternate view of the design.
mexzony said…
when you say the 10k preset PWM at the relevant pin#5 should be applied through a 0.22uF or a suitable low value capacitor so that it doesn't load the transistor and burn it, how do i apply it
Swagatam said…
I meant that the triangle waves should be fed via a 0.22uF or any small value capacitor to the pin#5 of the relevant 555 IC, and this pin5 should be also used as the load correction input
Swagatam said…
....a 10k resistor will need to be connected from the above pin5 to ground for correct operation
mexzony said…
Sir please i still dont get it.
1)triangle waves are fed to pin 2 of the relevant 555 while the 10k preset controls the input DC voltage into pin 5 of the relevant 555 so i dont get what you mean by "triangle waves should be fed via a 0.22uF or any small value capacitor to the pin#5 of the relevant 555 IC" as pin 5 is for inputing DC voltage.
2).a 10k resistor will need to be connected from the above pin5 to ground for correct operation.
if we connect an ordinary 10k resistor from pin 5 to ground then we then connect the 10k potentiometer or preset to thesame pin 5 and then connecting the emitter of the transistor to thesame pin 5 to enable voltage correction.is that it
Sir please explain how exactly step by step do we do all this as i am a bit confused with what you said we should do.
Swagatam said…
Actually the 0.22uF cap suggestion is not for the above explained design, it's for the pure sine wave version where we would want to use a modulating triangle or sine wave at the pin#5 of the 555 IC.

For the above design we can simply add a 10k resistor in series with the slider arm connection which connects with pin#5 of the 555 IC for preventing the burning of the load protection transistor
Please wats d name of d textbook u made reference to in d link below..... Can u send the pdf to tonisage321@gmail.com. Or get a link for the direct download. Thanks

Swagatam said…
Sorry, i don't have this book with me, i had only only a page of it.
mexzony said…
hello Sir,
A very happy new year to you and your family.
I was wondering if you know any links on how to make an inductor and LC filter circuits so that i can test the inverter using a proper LC filter at the AC output of the inveter trafo
basically i want to make an inductor on my own if possible.
Swagatam said…
Hello Michael,

Happy New Year to you too!

I'll try to update the design very soon in the above article itself.
mexzony said…
Sir actually its not about just the design but about the process of winding one ourselves like a step by step instructions so that we can adjust the inductor because the inductor values will depend on the switching and cut off frequency which could be different for some of us..
mexzony said…
hello sir
is the above inductor diagram a second order low pass filter?
Swagatam said…
You will have to do it by some trial and error, presently i have no formulas with me. the shown filter is a first order double pole filter circuit.
mexzony said…
Hello Sir,
i want to establish some facts with you
sir when i tested out the voltage correction system on the inverter with PWM diodes connected here is what i noticed using a 15-0-15/220v 1000w trafo
1)the gate voltageof the FETs read 2VDC with me viewing the 50HZ pulses broken down nicely into small calculated blocks and remember i could adjust gate voltage using the preset of the voltage correction circuit.
any way my first test was to adjust the preset up or down and it controlled the AC voltage nicely by adjusting the width of the pulses as i viewed it on my PC scope and so that is a pass mark.
2)at gate voltage of 2VDC with PWM on the output AC voltage read say about 157VAC. Now the 2VDC gate voltage means the average conduction voltage of the PWM waveform hitting the gates of the FETS so when i applied a load(a rechargeable lantern) the gate voltage still remained the same which is good.
3)Now the aim of voltage correction is to adjust the width of the pulses when load is applied so as to increase the average voltage at the gates of the FETs which will in turn increase conduction of the FETs automatically correcting the AC voltage output.Am i Right?
4)here is the main part
so with the first load plugged in,i then plugged in another rechargeable lantern maiking 2 loads and according to my assumptions the gate voltage increased from 2VDC to 2.41VDC which makes sense as the width of the pulses has become wider a bit so as to compensate for the extra load and i even viewed as the width (on time)increased on my PC scope which means so far so good.
5)Now heres the mini strange part
with increased width thereby increasing average PWM wave voltage to 2.4VDC i expected to get a slight increase in output AC voltage from 157VAC to say 157.5VAC since 2VDC is not far off from 2.4VDC.my assumption should make sense right?
6)Now what i got was a reduced AC voltage of about 153VAC and it stayed steady at that voltage but the gate voltage was still reading 2.4VDC so why the voltage drop when at 2VDC i got 157VAC.
it then occurred to me that a few factors might cause this and here they are
a)the iron core trafo which experiences increase in losses as frequency increases(proportional) which is why iron cores are not recommended for high frequency switching and this should make sense because gate voltage still remained at 2.4DCV so it acknowledges the extra load and adjusts the width which should mean slight increase in conduction yet output voltage reduced slightly.
i suspect the FETS are conducting more but the losses are occurring in the core of the trafo.
Based on this facts it is safe to assume that voltage correction adjust the width in proportion to the load but some how this is not fully reflected at the output due to iron core losses.
Sir what is your opinion since you are more knowledgeable than i.
i would really appreciate it if you could address each point i numbered with questions ending it.
by the way i used a parallel combination of two 12V/7AH batteries as power source.
Unknown said…
thank u Mr Swagatam for the filter circuit I know ur bright students will soon respond to this have a prosperous New Year
Unknown said…
Hello Mr Swagatam I see its kind of different to post our comments but the comment about saying thanks for the filter came from alex
Swagatam said…
first order, double pole filter
Swagatam said…
Hello Michael, please note that the voltage correction is not handle a drop in output voltage.

If the batts current is unable to cope up with the load curret requirement, the correction feature will become helpless, even though the mosfets would conduct more,it wouldn't be able to supply the required current resulting in a proportionate drop in the output voltage.

Another point with the above load correction feature is that it won't help to increase the voltage, it's designed only to cut-off the gate conduction by reducing the 555 pin#5 voltage to zero at a predetermined limit.

Meaning once the output is set to say 240V, the correction will not allow the voltage to go beyond this level irrespective of the load wattage, however if the load wattage goes beyond the battery capacity and due to this if the output voltage drops below the set 240V mark....in this situation the load correction will do nothing or rather will not respond as it would be beyond its control.
Swagatam said…
By the way I have recently posted a more responsive and accurate load regulator circuit, you can find it here:

Swagatam said…
thanks unknown! Happy New Year to you too!
Swagatam said…
hello unknown, comments are sent for moderation, so you won't see them immediately....what you are seeing could be a part of previously published comment......the recent comments can be seen by pressing the "load more" link at the bottom of the page.
mexzony said…
Hello Sir,
everything i typed was in the assumption that the battery current is able to cope with the load current requirement.
Also i agree that if the output is set to say 240V then no matter the load wattage as long as battery current is able to cope it should maintain 240V and yes it should not exceed 240V but maintain it and that was the point i was trying to make.
The fact that the mosfets conducted more with increase in gate voltage say that indeed the correction feature responded as it should but from your explanation since i set mine to 157VAC and it droped to 153VAC i think it has to do with the battery current as the battery is an old battery anyway.
My only encouragement is that the width of the pulses became wider alllowing for more conduction at the gate of the FETs.
I will look into your new post about the more responsive and accurate load regulator ciruit.Am already on it as a matter of fact.
Unknown said…
hello Mr Swagatam I tried the filter this improved the wave form to a sine wave signal but the fets arew running reall hot . Could u help us here again. Foor sure the filter works (alex)
Swagatam said…
hello mr.unknown thanks for the info, you can try reducing the values of the capacitors to some optimal value and check the results.
mexzony said…
i think that while the filter will work one should first of all know that LC filters have cut off frequencies so using a filter one should know its cut off frequency.
Mr Swagatam has given us a blueprint on how the filter should look like but it does not have to be the values exactly as it was posted so what you should do alex is find out the frequency st which the FETs are switching and then design the filter to have a cut off frequency proportional to the switching frequency of the FETS.
for example if the FETs switch at 2000HZ bearing in mind that the fundamental frequency we need is 50HZ sine wave the LC filter should be constructed such that the cut off frequency is at say 500HZ meaning it should be slightly higher than the needed 50HZ but at thesame time not too close to the switching frequency.
Personally i have found out that if the original PWM frequency is say 2000Hz then when we then apply the diodes to the gates of the FETs the switching frequency of the FETs is usually half or slightly more than half the original PWM wave form.
So for a PWM wave form of 2000HZ and when diodes applied to the gates of the FETS we should have a FET switching frequency of say 1000Hz -1100Hz.
Hope this helps.
mexzony said…
Hello Sir,
right now i am at a stalemate because as per the main PWM circuit i have confirmed it working and wave form confirmed and inshort the inverter works as intended but the only thing holding me back right now is the choice of core for the trafo.
i have made enquiries and i have seen true sine wave inverters made by companies even where i just had my industrial training as a student because i study physics on school and did some electronics courses the past semester which made me end up in this companies.
Anyway i have opened many commercial sine wave inverters and i saw that this inverters use iron core trafos so i am kind of confused now as to whether i should go ahead and wind an iron core or should still do more and more research.
Sir if you have got professionals who know about commercial sine wave inverters maybe you could ask them if iron cores are used and the frequency they are being switched at.
Honestly this trafo issue is what is holding me back for working further
i have also made inquiries about ferrite too am just waiting for answers.
Efficiency i what i am after here hence the confusion
Swagatam said…
Helo Michael,

you can also use a iron core trafo for the above expained design, just make sure the number of chopped pillars are restricted to two or three at the most.
nnaemeka mbachu said…
Sir is it possible to push more than up to 90% duty cycle into a trafo to make up the positive and negative cycles at an AC output.
i noticed that almost every inverter using push pull trafo uses a 50% duty cycle and i noticed that with 50% duty cycle there will be equal amount of spaces between the postive and negative AC cycles
Swagatam said…
you are referring to a crude modified inverter design, it can be implemented in the above explained design simply by removing the 555 PWM input. The spacing between the mosfet gate inputs from the 4017 IC will provide the required spacing that you are referring to.
nnaemeka mbachu said…
Sir can two diodes be joined is series just like two batteries so we join the anode of one diode to the cathode of the other making it seem like one new diode and if so is there any advantage to it.
2)also can we buffer the PWM wave form if possible.
Dont mind me just palying around as i try to understand some things regarding circuits
nnaemeka mbachu said…
The reason i asked about the diodes was whether it would make any difference to the speed at which they break the 50Hz square wave pulses. like i said just playing around.
Swagatam said…
No it will not make any difference, the waveform blocks will not reach ground competely and will stay at 1.2V above the zero line during zero PWMs.
Unknown said…
Mr Swagatam I tried the filter it works but it causes the fets to run very hot please help us here Sir
Swagatam said…
try reducing the values of the capacitors until an optimal condition is reached.
mexzony said…
Sir is it possible that this heating has something to do with flaw in the circuit because i have not had any unusual heating when using opamps and a comparator even with a capacitor at the output and i even plugged my laptop charger to test the circuit and the mosfets still ran normal.
Anyway its just my opinion.
mexzony said…
Hello Sir,
You know i have been thinking alot about this SG3524 circuit.Since it has inbuilt voltage correction which has proven very effective and fast this means that when we connect the diodes and break the square wave pulses it means that when the IC SG3524 adjust the width of the square wave pulses this will proportionately adjust the width of the broken pulses thereby maintaining stable output voltage so we will take advantage of the SG3524 IC.
Instead of trying to manipulate the main PWM IC the SG3524 just does the job for us.
I will study it in detail and let you know my mind but i honestly think it will work.
This might solve this issue of voltage corretion.
What do you think Sir
Swagatam said…
Mexzony can you show me your circuit design (using opamps)? I can assess both the designs and infer my opinion about them.
Swagatam said…
Hello Mexzony, 3524 IC won't break the pulses into small blocks, it will only reduce or increase the basic 50Hz pulses resulting the required RMS control with crude sine wave optimization.
mexzony said…
hello sir,
just wanted to let you know that i and my friend we are still working on this inverter and as soon as we have better news we will let everyone know.
Swagatam said…
OK, thanks Michael.
mexzony said…
Hello Sir,
i want to ask a technical question
I have this big 15-0-15/240V 800w trafo and i use it to test this inverter.
is it possible that when testing the voltage correction circuit to see if it will regulate voltage under different loads that this trafo may pose a problem in finding out if the voltage will remain stable because the input voltage of the trafo is way beyond the power supply voltage and it is always recommended that the trafo input voltage be equal to or less than the power supply voltage.
So in my case i use a 12V power supply yet using a 15-0-15 but in reality i should be using a 12-0-12 or 10-0-10 so this may affect me determining if the voltage correction system is working or not.
i even tested the trafo with the popular SG stablle inverter circuit.
Am i making any sense sir.
mexzony said…
Hello Sir,
i meant that we use the SG as the basic square wave oscillator but with the added advantage of its Automatic voltage regulation and then we introduce the PWM circuit to the gates so my thinking is that when the SG increases the basic 50Hz pulses the avreage PWM blocks will also increase and when the SG reduces the basic 50Hz block the avrage PWM blocks also reduces.
this is just a thinking.
mexzony said…
sir if you think it is feasible and you have anything to add i am all ears.like i said its just a thinking.
Swagatam said…
Hello mexzony,

SG3524 will not increase or decrease the 50Hz freq, this frequency will be fixed as per the selection of Rt/Ct. and the 50Hz frequency has no utility in the above explained 555 pwm circuit.
Swagatam said…
Hello Mexzony,

the voltage regulation which I have explained has no relevance with the primary (15/0/15) it's associated with the output voltage (240V) which is used to drive the IC after stepping it down and also for sensing the proportionate amount of rise or fall for the required correction.
mexzony said…
hello Sir,
is it possible for me to wind a trafo like a 10-0-10/300V or even if possible 10-0-10/350V
and it will be efficient or even 10-0-10/500v.
i just want to know if all we have to do is just increase the windings of the secondary.
Swagatam said…
hello mexzony, transformers can be wound as per individual preferences and specs, so it's possible.
mexzony said…
hello sir,
i want to ask if in all these battery charger circuits that have to use step down trafo capable of delivering high current needed to charge the trafo.for example a 12V/1000AH battery will need a step down trafo of maybe 15-0-15/220V rated at say 10A to be able to charge the battery and this trafo is installed into the charger bridge ciruit for rectification.
Any way what i am trying to say is that,
1)is there a circuit where i dont need to use a step down trafo instead the circuit can step down 220VAC to a lower AC value and then rectified with a bridge
2) the most important thing is that this circuit can deliver very high current maybe up to 100Amp if possible after the bridge rectifier needed to charge the battery and we should then be able to increase or reduce this current depending on the number of batteries we want to charge.
3) it should have automatic features that monitor battery level and things that make up a good battery charger.
i just dont want to use another trafo after the main inverter trafo if possible.
mexzony said…
hello Sir,
when operating the 4047 circuit as a normal square wave inverter i want to know
1)can i use a mosfet driver like ir2110 after the 4047 circuit to drive the mosfets as a basic square wave inverter and if so how do i connect this mosfet driver in push pull mode since i noticed that this drivers are normally used in half bridge designs where we have high and low side but for a push pull configuration it is usually low side driving that is involved.
Swagatam said…
helo Michael, a trafo does all these things together, it steps down 220v AC to 15v AC, allows the current to the required level, it also keeps the lethal mains isolated from the DC circuit and battery....so a trafo is a must and the only solution
Swagatam said…
hello michael, a suitable example can be seen in the following article.

mexzony said…
Hello Sir,
i know this may sound like a silly question but what happens if we connected two 1n4148 diodes in parallel?
would this allow the PWM to reach very close to 0V or ground as right now they are at 0.6V above ground?
also would this have an effect on how it effectively chops the square wave pulses.
Swagatam said…
Hello Michael,

even if you connect 100nos in parallel it will still show a drop of 0.6V, you have to substitute it with a transistor or a scotky diode for getting around zero drop
mexzony said…
hello sir,
1)what type of transistor and how do we connect it.
2)what type of schotky diode and will it effectively chop the square wave pulses.
i am exploring options so bear with me.
Swagatam said…
1) use BC557 (PNP), short base with collector, this becomes the cathode, while the emitter becomes the anode.
2)their are plenty of them you can Google, according to curret ratings, but these are costly.

the 0.6V drop across resistors in fact helps to create better modified sine waves.
nnaemeka mbachu said…
hello Sir,
you just took the word out of my mouth because the reason i was asking about trying to bring the voltage all the way to 0v or ground instead of 0.6V above ground was because i actually thought if the PWM went all the way down the eventual pure sine waveform after filtering would really improve but you just made this statement :
"the 0.6V drop across resistors in fact helps to create better modified sine waves"
please sir could you enlighten and convince me(cheeky laugh) me on how exactly it does this?
biannz said…
sir i want to try this circuit but my question is all the 12v sign should be connect together? as well as negative? i want to build 3500W how many of IRF540N should i need please help me with that i have a 3000W transformer including the pats list its right here on my table so im waiting for your respond be for i will starts thank you
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