Understanding SG3525 IC Pin Outs

The article explains the pin out functions of the IC SG3525 which is a regulating pulse width modulator IC. Let's understand in details:

Main Technical Features


The main features of the IC SG3525 may be understood with the following points:

  • Operating voltage = 8 to 35V

  • Error amp reference voltage internally regulated to 5.1V

  • Oscillator frequency is variable through an external resistor within the range of 100Hz to 500 kHz.

  • Facilitates a separate oscillator sync pin out.

  • Dead time control is also variable as per intended specs.

  • Has an internal soft start feature

  • Shut down facility features a pulse by pulse shutdown enhancement.

  • Input under voltage shut down feature also is included.

  • PWM pulses are controlled through latching for inhibiting multiple pulse outputs or generation.

  • Output supports a dual totem pole driver configuration.

Pinout Diagram of the IC









SG3525 PinOut Description


A practical implementation of the following pin-out data may be understood through this inverter circuit

The IC SG3525 is a single package multi function PWM generator IC, the main operations of the respective pin outs are explained with the following points:

Pin#1 and #2 (EA inputs): These are inputs of the built-in error amplifier of the IC. Pin#1 is the inverting input while pin#2 is the complementary non-inverting input.

It's a simple opamp arrangement inside the IC whose output controls the PWM of the output. Thus these pin outs can be effectively used for correcting the output voltage of a converter.

It may be done by applying a sample voltage from the output through a voltage divider network to the non-inverting input of the opamp (pin#1).

The fed voltage should be adjusted to be just below the internal reference voltage value when the output is normal.....

now if the output voltage increases, the sample voltage would also increase and at some point exceed the reference limit, prompting the IC to take necessary corrective measures so that the voltage is restricted to the normal level.

Pin#3 (Sync): This pinout can be used for synchronizing the IC with an external oscillator frequency. This is generally done when more than a single IC is used and requires to be controlled with a common oscillator frequency.

Pin#4 (Osc. Out): It's the oscillator output of the IC, the frequency of the IC may be confirmed at this pin out.

Pin#5 and #6 (Ct, Rt): These are termed Ct, Rt respectively. Basically these pinouts are connected with an external resistor and a capacitor for setting up the frequency of the inbuilt oscillator stage or circuit. Ct must be attached with a calculated capacitor while the Rt pin with a resistor for optimizing the frequency of the IC.

Pin#7 (discharge): This pinout can be used for determining the dead time of the IC, meaning the time gap between the switching of the two outputs of the IC (A and B). A resistor connected across this pin and ground fixes the dead time of the IC.

Pin#8 (Soft Start): This pinout as the name suggests is used for initiating the operations of the IC softly instead of a sudden or an abrupt start. The capacitor connected across this pin and ground decides the level of soft initialization of the output of the IC.

Pin#9 (Compensation): This pinout is not so important for general applications, just needs to be connected with the INV input of the error amplifier in order to keep the EA operations smooth and without hiccups.

Pin#10 (Shutdown): As the name suggest this pinout may be used for shutting down the outputs of the IC in an event of a circuit malfunction or some drastic conditions.

A logic high at this pin out will instantly narrow down te PWM pulses to the maximum possible level making the output device's current go down to minimal levels.

However if the logic high persists for longer period of time, the IC prompts the slow start capacitor to discharge, initiating a slow turn ON and release. This pin out should not be kept unconnected for avoiding stray signal pick ups.

Pin#11 and #14 (output A and output B): These are the two outputs of the IC which operate in a  totem pole configuration or simply in a flip flop or push pull manner.

External devices which are intended for controlling the converter transformers are integrated with these pin outs for implementing the final operations.

Pin#12 (ground): It's the ground pin of the IV or the Vss.

Pin#13 (Vcc): The output to A and B are switched via the supply applied to pin#13. This is normally done via a resistor connected to the main DC supply. Thus this resistor decides the magnitude of trigger current to the output devices.

Pin#15 (Vi): It's the Vcc of the IC, that is the supply input pin.

Pin#16: It provides the internal 5.1V reference for optional use. This pin must be terminated with a low value capacitor to ground.

Need Help? Please send your queries through Comments for quick replies!




Comments

Swagatam said…
Just use a 7812 IC for limiting the voltage to 12V for the ICs, rest everything will remain as is.
Swagatam said…
I have no idea about it, you may take the help of a professional trafo designer.
beelal saeed said…
sir if i want to use pin10 of the sg3524 as shutdown in my inverter how do i make the circuit to sense my battery low voltage and trigger the shutdown
Swagatam said…
beelal, pls refer to this example for the connection details:

https://homemade-circuits.com/2013/01/modified-sine-wave-inverter-circuit.html
Mohammed Hanafy said…
Hi
i need help about the sg3524 i build an inverter with it but my problem is that i only get 1.5vac form pin 11 and pin 14 and i know it should be at least 2.5 volt so my inverter is not working please help
Swagatam said…
check the peak voltage at those pinouts with a peak voltage detector, it should be equal to the battery voltage, or adjust the PWM pin preset for correcting the output to the desired limit.

In any case the mosfets will conduct, albeit with different RMS levels.
nomi said…
I have the same issue.
Swagatam said…
check the supply voltage, it may be too high or there could be soem other incorrect connections.
nomi said…
Hello sir .i have built a car smps based on sg3525.on off load my dc rectifier heat up gaudily,i am using 12v 1.5 AH power supply.when i attach a car battery my rectifier blows with in seconds and in result my mosfets also blows.i cannot figurout where is the problam.please help me with that.
Swagatam said…
Hello Nomi, It indicates that your SMPS is wrongly designed or constructed, a bridge will never heat up without load or under correct loads
Dear Sir
I want know how to calculate RT AND CT
Swagatam said…
Dear Rashabtha,

f = 1.3/Rt.Ct

Rt in kHz, Ct in uF and f in kHz
revathy lal said…
how do we calculate dead time? whats the formula for Rd
Swagatam said…
please check the datasheet of the IC, it might be there
Dear Swagatam Sir,

Can I use this IC to synchronise 2 sine waves with a phase difference?

Thanks in advance.
Swagatam said…
Dear Faris,

please read the pin#3 explanation given in the above article, here sync feature becomes relevant only when more than one IC is involved and all the ICs need to work with a single oscillator frequency, secondly the IC is not designed to respond to sine waves, it'll ultimately convert all frequencies to square waves...
Sir,
can you please suggest me any method by which I can synchronise two sine waves of high voltage?
Swagatam said…
Faris, you'll have to explain me the whole application that you are trying to implement, only then i'll be able to suggest you something...
Johnny Perez said…
If I'm getting no output from A and B and shutdown pin is low, what is causing outputs to stop? Thanks!
Swagatam said…
shutdown pin should be at "low" to enable the A/B pins functioning....there could be some other fault in your circuit
victory said…
Hello sir i have constructed an inverter based on sg3524 with 2 irf3205 mosfet which is supposed to deliver 300watt and at the output i get 300vac and adjust it to 220vac using the preset and my transformer is 9-0-9 300va but when i connect a 20watt cfl bulb it works fine but if i connect a 60watt load the output becomes 0v and transformer stops humming but once i remove the 60watt load inverter comes on immediately and after sometime it starts to on itself and off itself at a period of about 3seconds...pls where could the problem come from as i'm using a 12v 36amp battery could this be as a result of faulty battery? Because when i bought the batt. I checked the voltage with a dmm and it reads 21v and then decreases fast to 13volt also i didn't charge it when i bought it before using is anything wrong with the battery? If yes can i still power the inverter with an 18amp bactery as i will buy new one if the new battery i bought would be faulty..thanks in advance
Swagatam said…
Hello victory,

a good 12V battery of any kind can NEVER show 21V at any cost...so definitely your battery could be severely faulty...and using a battery for an inverter application without charging is another grave fault that one can make...so both ways it's the battery that looks defective.

you can use any AH rated battery, that will not harm your inverter in any manner...but just make sure it's 12v rated for your 9-0-9v trafo inverter
victory said…
Also this is what i observed the drain voltage of the fet on no load at pin 11 of ic is 10.5v and at pin14 is 8v but when i connect the load to it drain voltage becomes 0 which makes the transformer to stop humming is that a clear indication that it's the battery cos i don't want to buy another battery and end up having the same result and since the inverter is producing the desired voltage i don't see anything wrong with it.
Swagatam said…
just connect a voltmeter across the battery terminal while the inverter is loaded, if the voltage drops to zero will indicate a faulty battery...you can also try attaching an ammeter in series with the battery positive and check the current while the inverter is loaded...if the current reading is too high then your inverter is faulty.
Jose Mimbela said…
I want to work with two IC SG3525, both working at 50 kHz but one commanding the other, so that the waves are synchronized outputs A, also the output waveforms B also synchronized.
Please send me a sample schema, my email is jmimbelac@yahoo.es

Thank you
Swagatam said…
connect the pin4 of the IC which has Rt, Ct configured at 50kHz, with pin3 of the other IC without Rt, Ct....that's all ....now both will be synchronized at 50kHz
Jose Mimbela said…
Thank you sir, I checked and is correct.
victory said…
The inverter is faulty i replaced the mosfet with original one as i was deceived with a fake irf3205 mosfet the new one powered a 200watt load very normal and my tv works without noise as if it's a pure sinewave
victory said…
The inverter is faulty i replaced the mosfet with original one as i was deceived with a fake irf3205 mosfet the new one powered a 200watt load very normal and my tv works without noised
victory said…
Pls what will be the dc voltage of a 15vac transformer after rectification and is their anything wrong with connecting the dc voltage directly to my 12v 36amp battery Will reversed current from the battery destroy the bridge diodes,,also pls tell me the time that my 12v 36amp batt. Be fully charged when charging with a current of 2amp 3,adding a diode to the positive line after rectification will it reduce the voltage
Unknown said…
Please explain the frequency calculation
Swagatam said…
after smoothing it could be well over 20V, you can use it if the current rating of the trafo is not over 4 amp

No, diodes of the bridge will never get destroyed by the battery power.

yes, after 10 hour of charging at 3 amp rate your battery should fully charged.....a series diode will reduce only 0.7V so that's fine if your trafo is already 15V rated.
Swagatam said…
sorry, the charging rate should be at least 4 amps...3 amp could take around 20 hours for full charging
victory said…
Sir can u please suggest what the problem might be i rectified a 12vac and it producer 13,8v with 9amp current and my battery voltage is now 11,4volt and so i NEEDED to charge it but when i connect my multimeter in series with the battery when connected I discovered that the battery is only drawing 0,4 amp whereas the current of my charger is 9amp pls what could be the problem or is that normal? I really need to charge the battery 12v 36amp (2)i also constructed ur automatic changeover circuit using relay but when i connect the load to the pole and initiate mains power to the nc the bulb lights well and once i apply dc to the relay coil it offs the light but i see some sparks inside the relay which makes the light to flicker what could be the pro,
Swagatam said…
victory,
what did you use for the filter capacitor? make sure it's rated at at least 20,000uF/25V...because after rectification the output from your power supply is supposed to be above 15V, and not 13.8V

for the relay problem, just connect a 220uF/25V capacitor parallel with the relay coil, and check the response
victory said…
The 15v is it on no load also i want to charge the battery with 14.4v not 15v as 15v will damage
Swagatam said…
I think I just forgot to tell you that the input current for your 36AH battery should not be more than 5amps...so I think 9amp is way too high....or probably you could use a LM338 current limiter circuit in the middle for correcting the issue.

after connecting the input voltage must drop to your discharged battery's voltage level....if it's 11.5V then initially the connected supply should drop to 11.5V and then gradually rise as the batt begins charging....
Swagatam said…
15V input will not damage the battery if you use an overcharge cut off circuit or manually switch OFF as soon as the battery reaches 14.4V...
victory said…
We don't have any high amp voltage regulator here in nigeria although i'm a Biafran
victory said…
And almost everything here is kinda fake
Swagatam said…
you can try making the simple high amp regulator as explained in the following article:

https://homemade-circuits.com/2015/03/100-amp-variable-voltage-power-supply.html
Unknown said…
Thanks sir for the explanation
I want to control pwm duty factor from 0-100% is this possible? i shorted pin 9 & 1 and pin 2 is shorted with 16 and i am using vdr from pin 16 to vary the voltage of pin 1 to control duty factor....
Swagatam said…
I don't think the connections are correct, it should be as shown in the following article:

https://homemade-circuits.com/2013/01/modified-sine-wave-inverter-circuit.html

ignoring the D5 connection, P2 can be used for controlling the duty cycle.
victory said…
Pls sir for a 12v transformer to output 15v after rectification that will be at peak voltage but when there is lower voltage it gives 12v dc so it's advisable to use a 14-15v transformer
Swagatam said…
In that case you can use a 24V or 18V trafo and regulate it to 14.4V through a LM338 circuit...this will take care of any low voltage situation and give a perfectly constant output for your battery
victory said…
We don't have any voltage regulator apart from lm7812 here in nigeria.pls sir can u pls tell me why my sg3524 inverter keeps burning the mosfet after some minuites of operation despite being placed on heatsink and not overloaded i'm only running a 100watt load on it.the mosfet is irf3205..could it be the ic?
Swagatam said…
Victory, please try connecting the mosfets through BJT drivers as shown in the following example, and see the response:

https://homemade-circuits.com/2015/05/simplest-pwm-modified-sine-wave.html
victory said…
I've tried the bjt stage yet the same thing happens what could be the problem
Swagatam said…
disconnect the transformer from the mosfets and connect 12V car headlamps across drain and positive of each mosfet, if it still burns then definitely the fault could be assumed to be with the IC output...
Swagatam said…
by the way did you connect freewheeling diodes across drain and source of each mosfets???
victory said…
No.what is a freewheeling diode and what type of diode should i use and also the connection details.
Swagatam said…
connect each 1N5408 diode across each of the mosfets...cathode to drain, and anode to source pin of the mosfet
victory said…
I replaced the ic and it works fine now but pls(1)how many hours or minuites will my 300watt inverter power a 220watt load using 12v 36amp battery(2)what's the positive voltage pin10 of the ic will receive before shutting down the inverter(3)i want to rectify a 15v transformer to charge battery but i know that the voltage will be up to 20vdc after rectification and so can i connect a 12v cooling fan at the output so as to reduce the voltage to 15v or should i use a 12v lamp
Swagatam said…
1) back up can be expected to be not more than 1 hour.

2)pin10 must receive a permanent high or positive from the battery to shut down.

3)a lamp in series will work better than in parallel with the output, although both the methods are crude and not much recommended.
Vijay Shankar said…
What is the voltage supply at pin10 to shutdown the Ic
victory said…
Happy new year sir..this marks the 3weeks of my inverter functioning effectively pls can you tell me how i can eliminate soft start in my sg3524 inverter as it affects my appliance during automatic changeover when mains is unavailable as it trips off my tv and then on the tv whereas i want it to run automatically without switching off during changeover...i used 100uf cap for a relay power supply so the problem does not lie on the automatic changeover circuit and am 100% sure on that (2)what is the maximum power of an inverter with a single irf3205 in each oscillator of the ic?
Swagatam said…
Happy New Year to you Victory!

Do you have any capacitor connected across pin#8 and ground of the IC?
If yes then just remove it to eliminate the soft start effect.

mosfets don't decide the output wattage they are only rated to handle it....it's the battery and the trafo which are responsible for the power output ..

..IR3205 will easily handle upto 400 watts
victory said…
Pin8 is connected to ground no cap i only have a 100nf cap on pin 7 and 100k resistor on pin6 it is sg3524 not 3525
Swagatam said…
pin8 capacitor is only responsible for any sort of soft start effect, if there's no capacitor at pin8 then the reason could something else....try keeping the pin8 open or disconnected with ground
victory said…
Pls sir i was asked to construct a pure sine wave inverter(not modified sine wave) using sg3525 and 555 ic or 4047 ic as my final year project to be passed on march 24th pls can u help me with a circuit diagram and also if you have any schematic of a pure sine wave (not modified)inverter not modified sine wave you can also send me the link but the most important thing is that it must be pure sinewave and have pwm feature
Swagatam said…
victory, any inverter that uses PWM is a modified sine wave inverter...so better clarify the exact specs from your seniors, if possible get the waveform image which you are supposed to achieve.
victory said…
The waveform should look exactly like that of ac mains and that is pure sine wave
Swagatam said…
you can referring to the following article which shows the waveform images of a pwm based sine wave inverter

https://homemade-circuits.com/2013/10/modified-sine-wave-inverter-circuit.html

using pwm you cannot expect anything better than this.
victory said…
That is a modified sine wave inverter pls i need a circuit of a pure sine wave inverter
Swagatam said…
presently I do not have the exact circuit that you are requesting....If I find it I'll let you know
NicolaBarlabà said…
Hi i've a problem with sg3524 used in single ended mode in a buck converter. The problem is that the output freq seems to change (i don't mean the duty cycle but freq of output waveform between Collector and Emitter pin). How is it possible? it is set to have something like 60kHz, but i could see it is very lower, as 70 Hz. The circuit is the same of application note with only difference that i used p-mos and not p-darlington. Thank you
Swagatam said…
Hi, test the frequency at the base of the transistors and at the output of the transformer, if these are showing 60kHz then your IC is working normally,otherwise you can disconnect the BJTs from the IC outputs and the check the frequency on the output pins separately.
Qasim Alazze said…
Hello
Actually, I am working with sg3525 to build inverter 12 DC to 240 AC with f 50 Hz
But I have problems that output is not 50 Hz nor 240 volt
I don't know what is my problem?
So can help with that ?
Swagatam said…
first check the frequency at the output pins of the IC....both pins must oscillate at the 50Hz rate
Plss wat should be the voltage at pins 11 and 14 whn it hasnt been connected to mosfet?
Am designing a DC TO DC booster, anytime I connect the mosfet and high frequency switchin trafo only one mosfet get hot n destroyed. Plss wat could be the problem?
Swagatam said…
the peak voltages at these pinouts will be equal to the supply voltage, but their average voltage will be around 50% less than the supply voltage and will also depend on the PWM set through the pots at pin1/2

first confirm the frequency at these pins using a frequency meter, and this frequency should chnage as Rt or Ct is changed...., and the mosfet should be close to these pinouts for correct functioning....use a PCB for it, breadboard might not work
Adi shiekh said…
Hello sir..iam adnan. and iam working on a project in which i need to built an inverter of output frequency of 1MHz. as mention that in sg3525 built in oscillator whose frequency range is 100KHz to 500KHz. so i have to ask that can i use this ic sg3525to produce pulses of this switching frequency if not then plz recoment me an ic that can work on this switching frequency so i can get pulses to operate mosfets with desired switching frequency.plz
Swagatam said…
Hello Adi, I think the best oscillator circuit for getting high frequencies without issues is a transistorized astable using BC547 or similar transistor.

IC 555 can also be used for the same.
Adi shiekh said…
can you send me any link regarding to this issue so that i can make circuit arrangement for this frequency plz. because i dont have any idea about this circuit arrangment.
Adi shiekh said…
and one thing more sir g. can i use sg3525 for less than 500khz switching frequency mean for 300KHz inverter?????
Swagatam said…
yes that's possible.
Swagatam said…
here;s the link for the transistorized inverter:

https://homemade-circuits.com/2012/09/mini-50-watt-mosfet-inverter-circuit.html

you can decrease C1/C2 values for getting any desired high frequency depending on the T1/T2 MHz rating
Leong Kit Gan said…
Hi there, can I have some advice from you? I am currently working on an inverter project. I have generated three SPWM, with each 120 degree phase shift from each other. I am wondering if I can use the SG3525 to generate the other three complemented PWM signals with dead time? Is there a direct PWM input to the SG3525 and by-passing the internal PWM generator block?

Are there any alternative solutions for my application?

Thanks!
Swagatam said…
Hi, sorry I am not quite sure about how the IC could be triggered with an external PWM....By the way the IC has only two outputs, so getting three outputs may not be possible.
Swagatam said…
Hi, why did you have to replace the fets?

you might be using wrong fets or there could be some other reason....

It cannot be because of the IC, because the IC output can be configured with as many mofets as you may want
please make sure the fets are connected very close to the IC output pins.

You can read the following article for more help

https://homemade-circuits.com/2013/09/mosfet-protection-basics-explained-is.html
leela said…
hi,
im working on half-bridge LLC resonant converter used to drive LEDs(40v and 1a). is sg3525 is suitable for this converter??? or any suitable ic for this converter.
Swagatam said…
Hi, I don't think SG3525 can be used for half-bridge driver application, you can try the following concept for your requirement

https://homemade-circuits.com/2013/09/half-bridge-mosfet-driver-ic-irs21531d.html
leela said…
thank u for quick response sir....im working on voltage mode feedback control for half bridge converter. i have selected ucc25600, but it requires a center tap transformer (isolation transformer between mosfet and ic )for driving power switches. it would be helpful if u suggest any other ic for feedback purpose without use of isolation transformer.
Swagatam said…
Thanks leela, the feedback control is a secondary issue, the primary issue is the half-bridge topology which can be implemented only through a specialized IC as suggested by me earlier. Other ICs like SG3525 will require a center tap transformer for the operations.

You can Google for "half bridge driver IC" and see if you can find other options also of your choice...
leela said…
thank u sir......
Basil Mathew Tharian said…
Can use XR2203 ,PLL and zero crossing circuit .go through these the ic datasheet to get the idea .
Mihai S said…
Hello,

I am designing a buck converter for a solar charge controller. I am using SG3525 and IR2110. I am experiencing a strange reaction:
- If I connect the MOSFETs directly to SG3525's outputs, then all is good;
- If I connect the IR2110 driver to the outputs of SG3525, I find the pulses in the outputs of IR2110 but when I connect the same MOSFETs, one of the SG3525 outputs stops. I only get the pulses on one of the channels. Why does it stop pulsing ? If I disconnect the MOSFETs from IR2110, both channels pulse again.
All this test is done with the feedback pin linked to ground, so SG3525 sends a 50+50 duty cycle.
Please give me an idea what is happening.

Thank you,
Mihai.
Swagatam said…
Hello,

that's strange, try connecting LEDs with 1K resistors across the IR2110 pinouts and check how the LEDs respond.....or try connecting a resistor right across the gate/source of each mosfet and see if that helps.

you can also check the issues using BJTs instead of mosfets to learn if there's any difference in the response
Swagatam said…
by the way there's an easier alternative in the form of the following design

https://homemade-circuits.com/2015/05/5v-pwm-solar-battery-charger-circuit.html
My inverter is not turning on my 95watt LG television. It works fine with other loads but not with the TV. When I first turn it on, it attempts to come on but draws the power down and it will go off, it keeps repeating itself. I'm using sg3524 oscillator with feedback using optocoupler. Could it be that my feedback response time is slow?
Swagatam said…
It could be because your battery is not rated to hold 95 watts, the battery should be at least 25AH rated and fully charged.

Swagatam said…
Thank you Hiram, sorry unfortunately your first request is not feasible on this planet, because no system can produce an output that may be even close to the input value.

2) If you are using a lead acid battery then you must charge it for at least 12 hours at C/10 rate in order to maintain good health of your battery...or you can opt for a Li-ion battery and get it charged within a couple of hours.
Hiram Kumado said…
Please can you recommend me changing circuit​ that can charge two 12volt 90AH car battery in some hours? (2) please can I use two NPN thus TIP41 to boost the output of the SG3525 by connecting the base of the NPNs to each line before connecting it to the MOSFET?
Swagatam said…
It is not recommended to charge lead acid batteries in less than 10 hours, still you can try the following circuit:

https://homemade-circuits.com/2014/03/fast-battery-charger-circuit.html

your second request is simply not required...
Hiram Kumado said…
Thanks for the reply.
Adrees mohmand said…
Hello Sir.!
Hope you are good. I learn many basic knowledge for you blogs. i have question.?
how to control pulse width through sg3525. when i increase the feedback voltage at inverting terminal compared to reference voltage at non-inverting terminal i-e 5.1v, and connect the prob of oscilloscope at the output stage, so the wave form abruptly goes to zero. and when voltage at non-inverting terminal is slightly high than inverting i get maximum duty cycly i.e 49%. so suggest me how can i decrease the pulse width.?
Swagatam said…
Hello Adrees, I am glad you are learning from my blog...

the feedback should be automatic and should be connected with the mains AC, then it will not behave abruptly....

instead of a feedback you can use an external chopper circuit and integate with your inverter circuit, this will enable you to precisely adjust the PWM and also get a sine wave output for your SG3525 cirucit, you can refer to this post for more help

https://homemade-circuits.com/2016/08/sg3525-pure-sinewave-inverter-circuit.html
Adrees mohmand said…
Thank you sir.
I am going to read it carefully to achieve my goal.
Hi,

I used the Sg3525 to build a DC-DC converter running at 180V DC. I managed to get about 178.6V which is pretty close to my design so I guess should be fine. Before I connect it to my 2 mosfets in push-pull, pin 11 and 14 shows quite a perfect square waves on my oscilloscope. But when I connect it to my mosfets and transformer, the square wave seems to be distorted into a slim triangular sharp edge, but I still get the the output I need. Is there anything wrong?

Thanks.
Swagatam said…
Hi, there's nothing to worry, that usually happens due to the small spikes and other form of diturbances generated by the transformer induction switching.

You can improve it by connecting a high value capacitor across the battery terminals and also an appropriately selected high value capacitor across the trafo output winding.
Hi,

Thanks for the reply. I did include the capacitor on the supply and output when I tested it. But the square wave is not simply distorted with spikes, it changes completely to a triangular wave and the duty cycle seems to be off because it became slimmer, that's ok too? Only happens when i connect it to the moafets. Output seems right though.

Also, dont mind if I ask one more qns. I'm trying to test this DC output to try and power up a smps laptop charger. In smps, first stage is bridge rect, so feeding ac and dc doesnt matter much right? Excluding some losses if using DC due to diode. I tried connecting the dc output to the live and neutral pins of my 3pin plug, leaving the earth pin unconnected. It seems to be able to charge up but the charger seems to be on and off constantly instead of charging constantly. For this testing, I'm using a dc power supply to provide 12V for my circuit, it seems to keep flicker as well from CC to CV. Is it because of the limitations of the dc supply and i should use a 12V battery instead?

Thanks.
Swagatam said…
No that's not OK, the waveform should be like rectangular wave, not triangle wave, try removing the output capacitor and check again? by the way are you using a transformer with the mosfets? because you mentioned that the output is DC? I am not able to get what exactly are you making? is it an inverter or a DC to DC converter?

So, i check output directly from transformer secondary without cap?

I'm designing a dc-dc converter using sg3525 by push-push. So I'm using 2 mosfets with a HF center-tapped transformer that i coiled myself. Then i have a bridge rect and a output capacitor at the secondary side to get my DC output.

I'm trying to power up the laptop charger using DC instead of AC. The laptop charger is assumed to be smps-based so first stage is usually rectification?

So, feeding DC or AC doesn't really make a huge diff in smps-charger since it will be processed to a lower DC volt.

But my issue is that my charger seems to on and off repeatedly. I'm thinking the mosfet issues. So I'm wondering what could be the issue or does it not work? But I've seen ppl testing this concept and working successfully.
Swagatam said…
OK got it, I think the charger is switching ON/OFF due to lack of current and your 12V power supply could be responsible for this, try with a higher current 12V supply and check the effect.

However, an easier approach would be to use a 12V to 24V boost converter and directly connect your laptop with it...the 220V SMPS charger may not be required
I suspect it's my 12V power supply as well. Im using the typical DC power supply used in the labs and i think the maximum current they can supply is only about 3A. The power supply seems to flicker from CC to CV mode as well when the charger on and off.

However, i dont have access to 12V batteries to test out the different effects or if it's really my power supply that is causing this issue due to the lack of current.

I've thought of that but using the charger to test is one of the requirements of my testing.

Thanks for your help. I'll try to verify my power supply first.
Swagatam said…
OK fine, but if the input is really 3Amp then that should be quite sufficient...??

I would suggest a single 12V to 19V converter and use it directly for charging the laptop battery, this looks technically more correct....
I'm still having issues with my output from the sg3525. If i just connect my scope to pin 11 and 14 without connecting the mosfets and transformer yet, i get almost perfect square with a reasonable capacitor on the supply. The +ve duty cycle is about 45%.

I tried changing my mosfets for pushpull and it seems to get rectangular outputs now. However, when i connect the entire circuit, including the transformer and stuff, the duty circuit shrink to 13% and the frequency seems to shoot up to a much larger value. My circuit was made to be 100khz sw frequency.

Is this normal? I think i should fix this first if this is an issue before even moving on to other stuff.
Swagatam said…
may be you can try changing the mosfets, the mosfets seem to be the culprits, alternatively you can try replacing the mosfets with TIP142 BJTs and see if that solves the issue
Zvs said…
I made simple inverter circuit using sg3525 but emitter output pin of ic have different voltage about 1 volt difference.
Is my ic faulty
Swag said…
please provide the voltage details and the frequency details if you have measured it....I'll try to assess
Zvs said…
The voltage is 12 volt frequency is 50 hz according to the calculated value (470 ohm for rd. 157k ohm for rt and. 1uf cap)
Swag said…
you must confirm the frequency with a frequency meter, and voltage with a voltmeter, if V is around 6V at 50Hz then the 1V difference can be ignored
Daniel Sawyer said…
The issue is a power supply with an sg3525 is not generating output on pins 11 and 14. Pin 9 is connected through a diode and a resistor network to pin 1. Pin 9 is 5V and pin 1 is about 3 V DC. Pin 2 is connected to a voltage divider network to Pin 16, Pin 2 is about 3V DC. Pin 4 is connected to a timing circuit of 5% duty cycle 250KC pulses. Pin 5 and 7 are connected to a 250KC .75 to 3.7 sawtooth . Pin 6 is 3.7V DC. Pin 8 is 5.4 V DC. Pin 10 .3 V DC. Pin 12 GND. Pins 13 and 15 are 8.8 V DC. Pin 16 is 5.1 V DC. Pin 3 is open. Does anyone see something obvious as to why there no output on 11/14 ?
Swag said…
You can try other slightly different configurations available across other websites, if still the output does not appear for all those attempts, then your IC may be faulty.
Daniel Sawyer said…
Thank you for that lead. As an operations question, a 3525 block diagram shows 3 inputs to the PWM. The input on the PWM diagram shows pin 5 as plus and pins 9 and 8 as negative. As noted above pin 5 is ramp between about .75 VDC and 3.7 VDC, while pin 9 is about 5V and pin 8 is about 5 V. The designations on the block diagram represent pin 5 as positive input on the PWM while pins 9 and 8 being negative . This is the reverse of the measured values. Does this imply the PWM is locked out? Does this imply that could be the error? Will the PWM operate with pin 8 higher than pin 5? Will the PWM operate with pin 9 higher than pin 5? Is there a description of the requirements for the PWM to operate? Is it sufficient for pin 5 to higher than either of pins 9 or 8? Or must pin 5 be higher than both pins 8 and 9 for the PWM to operate?
Swag said…
sorry I am finding it difficult to interpret the opamp configurations since they are complexly interconnected with each other.
and also I am not sure regarding pin#9 which is the compensation pinout of the IC, how this pin is supposed to be configured?
You can refer to the following standard design in which it shows pin#9 attached with pin#1.
https://www.homemade-circuits.com/modified-sine-wave-inverter-circuit/
In this the PWM could be effectively adjusted simply by adjusting the voltage at pin#2
Daniel Sawyer said…
Thank you, I realize this is hard. In that circuit can you provide a description if the voltages on pin 9, pin 8, and pin 5 when the circuit is operating?
I have ordered some IC to test in a breadboard. That will help clear up a simple operation.
Thank you for you help.
Swag said…
sorry no, I do not have any information regarding those values, as you are about to buy new ICs so I think you will be able to learn about them easily through practical measurements.

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