Pure Sine Wave Inverter, Using IC 555

The proposed IC 555 based pure sine wave inverter circuit generates accurately spaced PWM pulses which imitates a sine wave very closely and thus can be considered as good as its sine wave counter part design.

Here we use  two stages for creating the required  PWM pulses, the stage comprising the ICs 741 and the other comprising the IC 555. Let’s learn the whole concept in details.

How the Circuit Functions – The PWM Stage

PWM pure sine wave processor stage using opamps and IC 555

The circuit diagram can be understood with the following points:

The two op amps are basically arranged to generate the required sample source voltages for the IC 555.
The couple of outputs from this stage is responsible for the generation of square waves and triangular waves.

The second stage which is actually the heart of the circuit consists of the IC 555. Here the IC is wired in a monostable mode with the square waves from the op amp stage applied to its trigger pin #2 and the triangular waves applied to its control voltage pin # 5.

The square wave input triggers the monostable to generate a chain of pulses at the output where as the triangular signal modulates the width of this output square wave pulses.

The output from the IC 555 now follows the “instructions” from the op amp stage and optimizes its output in response to the two input signals, producing the sine equivalent PWM pulses.

Now it’s just a matter of appropriately feeding the PWM pulses to the output stages of an inverter consisting of the output devices, the transformer and the battery.

Integrating PWM with the Output Stage

power transistor connection with pwm and transformer

The above PWM output is applied to the output stage as shown in the figure.

Transistors T1 and T2 receive the PWM pulses at their bases and switch the battery voltage into the transformer winding according to the duty cycles of the PWM optimized waveform.

The other two transistors make sure that the conduction of T1 and T2 takes place in tandem, that is alternately so tat the output o from the transformer generates one complete AC cycle with the two halves of the PWM pulses.

Waveform Images:

pure sine pwm images

(Courtesy: Mr. Robin Peter)

Please also see this 500 VA modified sine wave design, developed by me.

Parts List for the above IC 555 pure sine wave inverter circuit

R1, R2, R3, R8, R9, R10 = 10K,

R7 = 8K2,

R11, R14, R15, R16 = 1K,

R12, R13 = 33 Ohms 5 Watt,

R4 = 1M preset,

R5 = 150 K preset,

R6 = 1K5

C1 = 0.1 uF,

C2 = 100 pF,

IC1 = TL 072,

IC2 = 555,

T1, T2 = BDY29,

T5, T6 = TIP 127,

T3, T4 = TIP122

Transformer = 12 – 0 – 12 V, 200 Watts,

Battery = 12 volts, 100 AH.

IC 555 Pinout

IC 555 pinout details

IC TL072 Pinout Details

IC TL072 pinout details

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


Engnr Arsal said…
Dear brother ,
how can we convert the same circuit for high power rating like if we want to make it for 5KVA or 10KVA what changes should be made??
Swagatam said…
Dear Engr,

you can do it by replacing T1/T2 with mosfets and by using an appropriately rated trafoand batery
Rahul vijay said…
Sir could u plz tell me how to measure frequency using a Normal digital meter
Swagatam said…
you can measure frequency only if your meter has this facility.

check for a small horizontal "S" or "Khz" indicated on the dial, use this range for measuring Freq
Rahul vijay said…
A horizontal S ( as you said ) resembling a square wave is there in my multimeter. But when i am connecting the leads b/w secondary terminals of a 15 V ac transformer no readings is showing on putting this range. I think the transformer doesn't change the input frequency since it is a power transformet..... Is my way of taking frequency reading is ok sir ???'
Swagatam said…
yes it's the square wave symbol which is assigned for measuring frequency.
The transformer secondary should definitely show a 50Hz frequency on the meter when the above range is selected.

Your meter frequency range could be faulty or the prods are not making contact.
Swagatam said…
T6 switches T1/T2 simultaneously with the PWM pulses, while T3/T4 make sure that T1/T2 conduct alternately at 50Hz rate individually (100 times per second together alternately), it's as simple as that.
Arun Dev said…
It is very interesting the idea of different inverter design from your blog.
I have following some doubts
1). What may be the specifications of the battery ( Ah and V ) being used with a 300 W transformer to support a maximum load of 300 W ?
2). Can you please point out a modification to any pwm inverter like this to facilitate the feature of automatic load regulation. I found a similar one in your article (posted 6 days before ), but didn't seem like satisfying the requirement.

I think it only shutts off the ac out when the voltage rises a specified limit (say 230 V ). It doesn't stabilize the voltage at 230V at varying loads.
Swagatam said…
Thanks Arun.

300 watts usage would mean 300 watt consumption in one hour. so if you intend to use this operation for say 3 hours, then 3x300 = 900wats, divide this by battery voltage(12V) gives 900/12 = 75, means the battery should be 75AH rated but practically you would need above 100AH battery.

For voltage regulation you can refer to this post:

Arun Dev said…
Sir If i am gonna construct a PWM type of inverter, i have to use 24 V instead of 12 V along with a 230V/12-0-12 V transformer. Am i right ?
I am using the series configuration of two 12 V battery banks each of which is a parallel configuration of two 12 V 20 Ah sealed lead accid batteries, thereby getting an overall specification of 24V 40 Ah.
Now my second question is whethet this will be enough to support the required load, since by calculation Ah=900/24 =37.5 ?
I think it will support atleast 250W for the same time period.
Swagatam said…
Arun, increasing voltage will decrease the current requirement of the inveter, this the only advantage of using higher voltage trafo and batt, it has no connection with a PWM type or any ordinary design, you can incorporate higher voltage concept in any design.....however for full bride designs you will require a single winding while for center tapped you will require a center tapped trafo.

making series batery connections will not yield double AH, the AH will stick to 20AH only.
H. M. Ariful said…
Hello sir,
Can you please describe me what section of the circuit is making the pure sine wave..i meant that what section is responsible for pure sine wave?
thank you!
Swagatam said…
Hello Ariful,

It's the 555 IC which is responsible for making the PWM equivalent sine waves.
Ferry Effendy said…
Hi Bro, how are you? Hope you and your family all going well.

I am preparing to build this inverter (the 3’rd one after succeeding builder the 400 Watts inverter design circuit from your other post and the 1 KVA H-bridge with 4 N Channels mosfets).

Before I starting to build this one, could you please advise me to the following questions:
1. What is the closest value of the resistor + preset P1 to achieve the best amplitude setting; if I substitute it’s with 220K preset instead of 10K resistor + 1M preset as of your design (I have no 1M preset ready in hand). I still not own oscillator/frequency meter, so it would be helpful for me also if you can give me some indicator of voltage measurement at some important points.
2. I want replace the BDY29 with IRF3205 N-Channel mosfets and feed the gates voltage with 18 Volts supply line from an additional voltage doubling stage. So the TIP127 and TIP 122 can be replaced with ordinary small transistors such as BC547 and BC557 accordingly. I think doing this would become much more efficient. Do you think it’s could make sense?
3. Can I use 741 OpAmps instead of TL072?

Thanks a lot for your support.

Best regards,
Swagatam said…
Hi Bro,great to hear from you back!

According to me all that you have asked makes sense.

Use IRF540 instead as these would be easier to obtain.

for the opamps you can use two opamps from the IC LM324, will be much suitable.

I am not sure about the preset set up values you will have to check them out through practical assessments.

Do everything extremely carefully and step wise only that could lead you to success.

Ferry Effendy said…
Thanks for your fast response Bro,

I think I’ll postpone building this project, since without any parameter measurements at some important points and without oscilloscope is difficult for me to achieve the correct results, especially to your unusual design like this.
My understanding to your design is that you use the first OpAmps for astable-multivibrator which output (square wave) to be fed to the second OpAmps which is designed as Integrator, from where the triangular waveform output will be used to superimpose or chops the PWM output of the 555 IC.
Could you please explain me why you fed back this triangular output to the 1’st OpAmps also?

From your expert views, Is it possible to convert a sinewave produced from a Bubba oscillator or any other oscillator stage, which output swing at about +20 Volts and -20 Volts and frequency of about 50-60 HZ, which directly fed to flip-flop switch the NPN and PNP power transistors alternately without any driver IC?

Thanks Bro, I have learned a lot from you.
Best regards,
Ferry Effendy said…
Hi Bro, sorry me again.

Actually I have build the driver stage tomorrow with 500K variable resistor for adjusting the amplitude that I borrowed from my other finish project.
First I just connected the 10K resistor with it and measured the output of pin 2 from IC 555. Then I add another 510K resistor to the other end of potentio and measured again these output. But I could not sensed any fluctuated swing although the frequency preset (I used 220K preset instead of 150K) has been varied from zero to max. The voltage coming out from IC 555 pin 2 was at about 7 to 8 Volts, while at pin 3 vary from 4.5 Volts to 9.5 volts (with various preset setting).

Regards, Ferry
Swagatam said…
Hi Bro,

The opamp circuit is a standard design which I borrowed from the datasheet of the opamp, so I cannot say much about its configuration, it must be correct since it's designed by the experts.

BJTs or mosfets will never respond to sine waves directly, because each counterpart will swing to the highest voltage as soon as the saturation limit is reached which will result in a square wave output from the devices, and not sine wave.

Again I would say that without an oscilloscope it would extremely difficult to judge whether the circuit's producing the correct required outputs, so I think an oscilloscope is a must for a design as complex as the above one.
Ferry Effendy said…
Thanks for your reply Bro, I agreed with you. I'll take a break with this project.
Btw, I read your other post of inverter circuit using 556 IC, I'll study it first and read your discussion with other readers about all aspects that might be encountered while building this. See you there in the near next days.

Best regards, Ferry

Swagatam said…
Sure bro, you are on the right tracks, wish you all the best
khang ly said…
Hi Swagatam Majumdar
Is output transfo square pulse ?
Swagatam said…
Hi khang, yes it's square but pwm controlled.
khang ly said…
Hi Swagatam Majumdar
It's use fan or inductor loads ?
Swagatam said…
khang, yes inductive loads can be operated with it.
franco rossi said…
hello Swagatam,
I recovered a transformer with a center tap ups, but it is a 5.5 - 0 - 5.5.
I can use it for this project?
thank you so much
regards andrea
Swagatam said…
hello andrea,

it will do, the PWM will need to adjusted appropriately to suit the transformer specs
franco rossi said…
hi swatagam
thank you for your job and disponibily
dinda lestari said…
hi sir, I beg to back the scheme pwm led dimmer that works on mains voltage 6 volts. because most pwm led dimmer that I found, almost all the work on the main voltage 5v, 9v and 12v. Hopefully you can help me.Thanks
Swagatam said…
hi dinda, you can use a 555 PWM circuit, just google it, you'll find plenty of them online.
if you have doubts, feel free to put them here.
Hi Swagatam,

Could I use:
MTP3055VL, MTP3055 60V 12A, Field Effect Transistor

Instead of T1,T2(BDY 29)


Swagatam said…
Hello indigo,

yes it can used, just make sure to connect 1k resistors across the gate/source of each mosfet.
Swagatam said…
thanks Roger, so greetings from me too for Brian.

A better design can be seen in the following diagram, which has an automatic output voltage control feature too.


output power can be increased by upgrading the trfao and the battery AH.

Presently I do not have a ferrite core type inverter circuit but will soon try to post one as shown in the link.
Dear sir,
I made this circuit but it didn't work, I checked it 10 times with my friends and found no error in pcb and all parts work. is this circuit really working have you made it??? I made the circuit on Proteus circuit simulation but it didn't work also, thanks in advance.
Swagatam said…
Dear Omar, you cannot just make any circuit directly and entirely as it is shown and hope for success. That's not the way to go.

You will need to make each stage separately, check it separately and then proceed identically for the the remaining stages also.

The above circuit may have some minor faults which can be easily traced and rectified.

Did you check and confirm the frequency generating stages separately with an oscilloscope???

Did you check the output stages separately?

Proceed in the above manner you will definitely find the circuit working.
Ngarajan k said…
hi swagatam, please clarify me how does the battery get charged
Swagatam said…
hi Ngarajan, the above circuit does not include a battery charger section
Kaluya Moses said…
Please Engineer Swagatam ,
What a great opportunity to link up a gain? I have been struggling to post my comments on your BLOGSPORT but all in vain
Thanks, am very happy a successfully circuit I built which is " pure sine wave Inverter circuit"
And there are so many Interesting circuits from this site i need to build very soon
Swagatam said…
Welcome back Kaluya, I appreciate your presence...keep up the good work!
Kaluya Moses said…
Dear Swagatam,
Am ever grateful for your dedication to all electronic hobbyist around the world.
Engineer , my pure sine wave inverter i built is perfectly working , but still i need to be well versed about the following points :
1)How to measure or between which two points should read 200HZ and 500HZ
2) My oscillator outputs is between 8 to 9v AC when 12.8 dc is applied at the input is this ok? And what is the suppose voltage in particular for this case?
3) What is the transformer output(secondary coil)
I will be grateful to receive a feedback from you thanks.
Swagatam said…
Dear Kaluya, thanks!

The oscillator output voltage should read 50% of the supply due to 50% duty cycle, for 12.8V supply it should show around 6,4V

The transformer output will be as per your requirement, 120V or 220V

pls provide me the link of the design you have built.
Kaluya Moses said…
Kaluya Moses
Sep 26 (5 days ago)

to Swagatam
Hi Engineer Swagatam,
Thanks for the quick reply, I understood the two questions i asked for a helped right a part from the two points where should i press "my negative and positive probes" in order to adjust and get 200HZ and 500HZKaluya Moses
Sep 26 (5 days ago)

to Swagatam
Hi Engineer Swagatam,
Thanks for the quick reply, I understood the two questions i asked for a helped right a part from the two points where should i press "my negative and positive probes" in order to adjust and get 200HZ and 500HZKaluya Moses
Sep 26 (5 days ago)

to Swagatam
Hi Engineer Swagatam,
Thanks for the quick reply, I understood the two questions i asked for a helped right a part from the two points where should i press "my negative and positive probes" in order to adjust and get 200HZ and 500HZ pure sine wave inverter circuit schematic it is the one which is using 3 ICS (555) and CD 4017BE so please help me engineer.
Swagatam said…
Hi Kaluya,

the negative probe should be connected with the negative of the battery and the positive prod to pin14 of IC 4017 and pin5 of the IC2
Joremie Jutba said…
how many watts is ths inverter?
Joremie Jutba said…
hi sir what is the wattage of ths inverter?
Swagatam said…
it'll depend on the wattage of the transformer and the battery AH, and also the output power transistor current handling capacity....these parameters can be increased to any limits for obtaining any desired power from the inverter.
ainsworth lynch said…
could I use tip 35c to replace BDY29?
Ahamefula Levi said…
hello engr.
pls i have an idea iv been pondering on. its a method, i think, pure sine wave inverter circuits can be designed. i need to discuss it with an expereienced person thats why im contacting you. pls how can one discuss privately with you. may be your facebook or whatsapp handle or emial will do.
thanks for your anticipated reply.
Swagatam said…
hello Ahamefula, I am sorry you'll have to discuss it openly because it would be difficult for me to devote time on individual basis
Ahamefula Levi said…
ok then. here is what i think.

from my understanding of inverter operation, there is a unit to create d alternating pulses from a dc source, den this signal is fed to a tx for amplification to d desired voltage level....now d unit that creates this pulses determines if its a pure sinewave or modified or even square wave inverter.

What if a true sinewave motor(mini ac generator) is used to produce this signal and then this sinwave signal is used to switch some power mosfets appropriately wouldn't that be a better way of producing a pure sinwave inverter?

are my assumptions practical? shed some light on this please.

Swagatam said…
yes it could be possible but it could be a lot inefficient, I have already discussed the concept in one of my blog articles, you can check it out here:

Dear sir,
I have a pc ups rated at 600va
i measured the o/p volt it says 180v@2.2amps.

I wish to use a ceiling fan and i tried by connecting it, it works well. fan runs for about 20 mins. with noise
my question is that what circuit should i use at the o/p of the ups in order to reduce the noise from fan,
Also, tell me where does ceiling fans' wattage range.
Swagatam said…
Dear Sherwin,

try putting a 0.22uF/400V capacitor across the output of the inverter mains and check if the noise gets reduced, a coil can be also included in series with one of the terminals of the output for improving the effect.
Hi Swagatam Majumdar,
According to your direction, I have made the circuit but it seem do not operation. Perhaps you help me to repair it? If yes, please contact me via my email quangphucgl@gmail.com. Sorry for my bad English.
Swagatam said…
Hi Nguyen, this circuit is a complex circuit and will require a step wise verification, checking, adjustments and tweaking, etc it cannot be built and operated at one shot.

did you check the confirm the various stages first??
kikiloaw said…
it's hard to build. no available parts in my place :(
jk jose said…
I am of the similar stuff. Can you introduce yourself. Are you trustworthy enough to handle confidential research and development circuits from us to check with your resources as intellectual asset sharing. We are ready to pay if you have adequate infrastructure and fund to construct or simulate the circuit in orcad and check the credibility of my personal designs. I have one site launched for sharing it.
equipment designer since 1982
Swagatam said…
thanks for the offer, I would certainly want to do it.... completely free of cost, but only if you allow it to be published it in my website.
Hadie Hunter said…
Hello mr swagatam
T1 and T2 Can be replaced with mosfet or other?because in my place hard to find BDY29
Swagatam said…
hello hadie, yes they can be replaced with mosfets
hello sir, BDY29 can be replace with BD139 ?
what the filter output inverter for inverter ?
Swagatam said…
No, both are entirely different with their specs
mayokun deji said…
i want to use fet in place of T1 & T2 hw wil go abt it?and can i use d pwm out into d power stage of another inverter.cn there b any modification to av a steady 220volt like d sg3525 & sg3524.?cn dis b added to d sg3525 inverter to get a better sin wave output?tnx.
Swagatam said…
you can try replacing the T1, T2 with fets and see the response.

yes it's possible to use the PWM out to an external circuit.

you may have to employ the following design for achieving a steady output from the inverter


the 1N4148 could be eliminated and the collector connected directly with pin5 of the IC 555 via a 100 ohm resistor
mayokun deji said…
tnk u sir bt am confused.d circuit u recommended for steady voltage says d 1N4148 diodes should go to d gates of d fet and u said i should fix d 1N4148 ends to pin5 of d 555.dnt knw which to do.tnx
Swagatam said…
pin5 is an alternate suggestion.

in that case the 1N4148 could be eliminated and the collector connected directly with pin5 of the IC 555 via a 100 ohm resistor
Hi sirji!
I am Indonesian.
I am newbie in electro. but i was read many articles those you've posted and i interest to build it from a basically.
But sir, i have a confuse;
1st. As i see in the circuit, R12 and R13 are 33 ohm 5 watts.
But i have a mistake, it's couldn't to find in my town.
I just only find 0.33 in value of 5 watt.
Can i replace it with these 0.33?

2nd. can i replace the T1 an T2 by 2N3055 and what value that i'll get in wattage?

3rd. if i replace by it, what value of base resistors can i use?

Thank you for answer sir.

*Fadly Muslim
one more question sir,
What rate wattage of the resistors can i use in this circuit?
Thanks a lot for apreciate.
Swagatam said…
Hi Fadly,

you can use 3nos of 100 ohm 2 watt in parallel for achieving the 33 ohm value...I hope 100 ohm/2 watt or 3 watt will be easily available in your area, yes T1/T2 can be replaced with 2N3055

the base resistor can be the same, that is 33 ohm, if more power is required then you could reduce them a bit more to 22 ohms or 20 ohms.
Swagatam said…
except R12 and R13 all can be 1/4 watt resistors
thank you Sir, i'll try it. I hope i can do until it works.
I'm sorry, my English is worst.
once more thank you sir for answering my questions. ?
O'ow... i forgot any question, if C1 0,1uF, what capacitor matterial can i use sir and any voltage which can i buy it?
Swagatam said…
you are welcome John
Swagatam said…
you can use 0.1uF ceramic disc capacitor, it is normally rated at 50V
Finally i have finished it circuit, i made it with 2 transistors, 2n3055 that i use in tandem.

I think, i have placed every parts like in the schema and as like you referenced to me.

But i confuse, i don't have a battery at 100 amps and a trafo CT 12-0-12, 10 amps yet. and i want to try my first project.

In my home i have only a trafo 12-0-12 at 3 amps, and a battery 12v 5 amps.
Can i try it circuit by using them?

I hope you don't bored by my questions, sir. :)
Swagatam said…
I appreciate it but sorry that's not the right way to proceed, you should build the various stages first and confirm them using proper test equipment.

first test whether the opamps are generating the intended waveforms or not, then check the 555 response to these waveforms.

once these are confirmed then you can integrate the relevant inputs with your power transistor stage....and do more related tests before going for the final results
Jesus Te Ama said…
Lord blessings swagatam like this. I wanted to ask you if this circuit can be output to the transformer with mosfet transistors and how can I do it. I commented that I am still working on the inverter with the cd4013. a cordial greeting
Swagatam said…
thanks jesus, yes the power BJTs T1/T2 can be replaced with MOSFeTs
Jesus Te Ama said…
Muchas gracias por su pronta respuesta. Un gran abrazo swagatam
Swagatam said…
Eres bienvenido jesus
Muhammad Rawal said…
Sir i want to make a supply of 12v input can be 10v to 20v out put should temain same can it possible
Swagatam said…
for an inverter you will add a automatic voltage regulator
Harish Kaithan said…
Hi, can you please suggest a better alternate transistor for BDY29
Swagatam said…
You can try TIP35
Ainsworth Lynch said…
If I may ask..... saying that your true ac motor would be the best choice to create pure sinewave, how would you get the motor to spin to create electricity?

If its an off grid system then no electricity would be present and a motor requires electricity to produce electrical motion.

If you plan to use a mini generator that requires mechanical motion (spinning) to create electricity which leaves the question how would you get it to spin?
Swagatam said…
Not an AC motor, a DC motor would be required for making the sample sine generator....the battery can be used for spinning the motor...

I hope you have seen the below given article

Leonardo said…
Hi, I was able to build the circuit on a breadboard, and it worked without any problem, what I have a problem with is the PCB design, I can not get it to fit correctly without crossing lines, do you have any design? I'm sorry for my English, it's not very good. thanks
Swag said…
Hi, I am glad you could build it successfully, if possible please send a video clip directly to my email...

If the PCB tracks are crossing the lines, you can use jumpers in those intersections, normally it is always difficult to create perfect PCBs without jumpers
abubakar said…
thank you sir for d wonderful post
Swag said…
you are welcome!
Vignesh said…
Can I replace 150k preset by 200k preset?? Plz let me know sir
Swag said…
Yes you can do that, no problem.
Vignesh said…
Sirji can I get connection part picture or vedio of this project??!. I really wanted to finish my project ..I'm requesting u to send through mail ...plz let me know..
Mukesh Babu said…
Sir Leonardo, I have opted this as my assignment, I have really tried every available circuits on the web. It would so kind of you, if u provide some reference videos of the above circuit(In type of a step by step tutorial).
Assist me as soon as possible, there is lack of time constraint
Swag said…
Vignesh, at the moment producing a video will be difficult, but sometime in future I may surely update it. If you have any queries you may ask the same, I'll try to help.

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