SG3525 Pulse width modulation controller IC

Control-Integrated circuit for SMPS SG3525: Pulse frequency modulation and pulse width modulation are two types of techniques used in control integrated circuits for switch-mode power supplies. In Pulse frequency modulation technique on time of pulse remains constant but the frequency increases with the increase in load. But the Pulse frequency modulation technique causes some issues in switch-mode power supplies. On the other hand in Pulse width modulation technique frequency remains constant but the width of pulse changes with the change in load. The width of the pulse or on time increase with the increase in load. Pulse width modulation also resolves the issues which occur in Pulse frequency modulation. Therefore, Pulse width modulation is a preferred technique for control circuits of switch-mode power supplies.

Types of PWM controllers

There are many PWM ( Pulse width modulation ) controller integrated circuits available in the market just like SG3525. These PWM controllers ICs you can use very easily in your SMPS projects by connecting some external circuitry with them according to the selection of frequency. I will discuss these things in detail later in this article. There are two types of PWM controller integrated circuits:

The voltage control method used a feedback voltage by comparing it with a reference value to set a duty cycle of PWM. In return to control the output voltage of SMPS. While the current control method uses Output current from output inductor to compare it with the reference value and to set the duty cycle of PWM. I have used a voltage mode PWM controller in pure sine wave inverter. Sg3525 is used in Dc to DC converter part to control the output voltage and for switching of MOSFETS connected to push-pull converter chopper.

Introduction to SG3525

  • It is a pulse width modulation controller IC which has 16 pins.
  • It provides two pulse width modulator signal which is a complement of each other.
  • It is used to generate a PWM signal for power electronics projects and also for switch-mode power supplies.
  • It offers feedback circuitry to control the output voltage by comparing the feedback signal with a reference voltage.
  • It has a protection circuitry that shutdown the PWM signal based on the feedback current limit.

SG3525 pinout diagram

This is a pin configuration diagram and the functionality of each pin is provided in the next section.

sg3525 pinout diagram

Features of SG3525

  • It can operate with a supply voltage of between 8 and 35 volts. It may damage above 40 volts.
  • It also has an external oscillator synchronization pin.
  • It has a pulse to pulse shutdown capability.
  • It can operate with a frequency range of  100 to 400KHz.
  • It also provides a feature of versatile dead-time control between switching signals to turn on or off devices like MOSFETs, IGBTS and power transistors.
  •  The maximum power dissipation is about 1000mW.
  • Other similar integrated circuits are SG2525, UC3525.
  • For further features and specifications check datasheet.

DataSheet SG3525

How and Where to use SG3525

  • Sg3525 is a voltage mode PWM  controller integrated circuit. It is used in maximum inverters available in the market.
  • Even top inverters manufacture companies also use Sg3525 in dc to dc converter part of the inverter. It is a 16 pin integrated circuit.
  • It has two PWM outputs both are an inversion of each. Another advantage of  SG3525 is that it has a built-in totem pole base PWM driver.
  • If you want to know about the internal architecture of SG3535. Search its datasheet.
  • Output pins can driver semiconductor devices up to a current range of 50mA. For example, if you are using a switch that requires more than 50mA to operate, then you will have to use driver IC as MOSFET driver IR2110.
  • The description and functionality of each pin are given in the next section on the pinout of sg3525.

Working with the functionality of each pin

The above diagram shows the pin configuration of SG3525. Description of each pin is given below:

pin configuration
  • Pin 1 is an inverting pin and pins 2 is a noninverting pin. If the voltage on the inverting pin is greater than the voltage on the non-inverting pin, the duty cycle increases and if the voltage on the non-inverting pin is greater than the inverting pin, the duty cycle decreases. So you can use one pin for feedback through the voltage divider and one pin for the setting of a reference voltage.
  • pin 3 is used for the synchronization of two waves.
  • pin 4 is the output of an oscillator.
  • pin 5, 6 and 7 is used to set the frequency of PWM. Frequency can be calculated by using the following formula:

f= 1 / CT (.7 * RT+ 3 * discharge)

By adjusting the values of CT capacitor, RT resistor, and discharge resistor. you can adjust the frequency of PWM.

  • Pin 8 SS is used for soft starting for enabling output after some time. Greater the value of capacitance connected to pin 8, greater the soft-start time.
  • pin 9 is a compensation pin used with feedback to avoid rapid fluctuations in output voltage with the change in load or input voltage.
  • Pin 10 is shut down pin. IF shut down pin = 0 it will work and if shut down pin = 1 means connected with 5 volts it will remain in shut down mode.
  • Pins 11 and 14 are output pins. These pins provide input to MOSFETs and as I have already mentioned, there is no need to connect any Mosfet driver because sg3525 has a built-in MOSFET driver circuit.
  • Pin 13 and 15 are power pins. Vc should be between 5-35 volt and Vin should be between 8-35 volt.
  • Pin 16 is a reference pin and it is used to set reference voltage through pin 1 or 2. It can also be used to give 5 volts to shut down the pin in case you want to shut down sg3525 through a push-button.

Example Circuit diagram SG3524

Circuit diagrams of example below show the circuit diagram of sg3525 which generates two inverted PWM signals. Users can adjust the width of PWM using a variable resistor shown in the feedback circuit. You can change the variable resistor value to adjust the resolution of PWM.

output of sg3525
  • In the above circuit diagram feedback from the output is used to get regulated voltage.
  • It is discussed in detail in Dc to dc converter using a push-pull topology part.

Inverter Circuit diagram Example

In this second example, this PWM controller IC is used to generate a 220 volt AC supply from 12 volts dc. This circuit is based on SG3525A which is the same IC. Two Mosfets and ferrite core transformer are used in push-pull configuration mode. This example circuit provides power regulated voltage output with the help of the feedback circuit. Variables resistor R10 provide voltage regulation feature.

sg3525 based power inverter

SG3525 Applications

  • It is used for power electronics applications like pure sine wave inverters.
  • It is used to generate regulated voltage for dc to dc convert circuits like a buck converter, boost convert, cuk converter, and many others.

Other articles of pure sine wave inverter.

172 thoughts on “SG3525 Pulse width modulation controller IC”

  1. thank u for this circuit
    could you help me for calculations of wire diameter of Ferrite transformer (ER-35) for inverter ?
    150 -200 watt
    output voltage 330v of transformer
    input voltage 10 -12.5

  2. Where can I find model/library for the proteus sg3525 and how can I install it? I have been looking around, do you any info about it ? thanks

  3. Sir,
    I am going to use the SG3525 IC for PWM of a dual stage DC-DC boost converter, and I need the duty cycle for both the MOSFETs to be 78%. However, the datasheet says that the duty cycle range is from 0 to 50% for the IC.
    Can you suggest how do I get 78% duty cycle using the 3525 chip and that too without using the feedback or compensation features. Also can it drive two MOSFETs simultaneously?

    Please do reply and help me out because this is my final year project.

  4. let me know the availability of file for SG3525.If available please send the same in order to create a proteus 8.

  5. Hello Mr. Bilal. I tried this circuit in practice in H bridge configuration (12V supply and operating at 50z, a resistive load of 3.2k )but the problem is two of my mosfets (one from either set;IRF540) are getting hot like hell while the other two are warm. The output voltage is about 1V only. I cant figure out the problem. Is my mosfet not properly switching ? please help. IF u can please send the model of sg3525 for proteus to the following mail id:

  6. Hello!
    What’s the sawtooth peak voltage generated by the sg3525? I need this information in order to close the loop of a CC-CC converter.
    Please send me the library of SG3525. My email is
    Thanks very much!

  7. Sir my question is why you use SG3525 IC why not you produce PWM from the microcontroller? For pure sine wave inverter, you have used microcontroller for AC output. Why don’t you program microcontroller to get PWM? It really helps if you answer me.
    Thank You

  8. Hello sir, Thanks for this tutorial.I’m building PWM invertor using KA3525A by Using Eagle Software.Circuit I have done but to do simulation .mdl extension file is not avaliable for KA3525A IC.
    Can anyone please provide the model extension file of KA3525A .my mail id is
    one more question does SG3525A IC is same as KA3525A IC ?

  9. u got the sg3525 lib / model file for proteus.
    can u please send it to my mail (

    thanks you sir

  10. Sir i want to make a dc to dc converter for car amplifier.
    By using 50khz frequency i will not get sufficient current so i wand to reduce it to 20khz . And i need 200w power at output
    Can you please send me a circuit of pwm using sg3525 ic of frequency 20khz ?
    And if you don’t mind , i want some advice from you that hot how can i make perfect supply for the amplifier , and which diode will give good response on this frequency . Thank you sir

  11. How to synchronize the two SG3525. Give me a tip please I intend to use one at high frequency 24KHz and the other at low 100Hz. If anyone can help me, I will be very grateful.
    Thank you.

  12. Dear sir
    please i would like to know how to get 5ohz oscillation from the ic 3525.I calculated the circuit above from the formula and didnt get 50hz. Please help me out, Thank you.

    • According to the datasheet (KA3525A), guaranteed frequency starts from 120Hz and typically you can expect only down to 60Hz, so it seems you are out of luck with your particular chip or the real cap value within tolerance range (can be as bad as -80% for e.g. some SMD MLCC types) wasn’t verified.

  13. Dear Sir,
    Could you pls send me or publish the driver for UC2525 which you have used in this article.
    Thanks with regards

  14. IM making Capacitive Discharge Ignition for my bike . but when i discharge the capacitor to ground with scr the output supply also grounded . can i shutdown the ic by giving positive pulse on shutdown pin. my working frequecy for shutdown the ic could be 250Hz. is there any effect on ic or it takes time to shut down

  15. Hello sir im trying to connect the synchro of 100KHZ on pin 3 of the sg3525 i have A default frequency and periodic cycle! can i possibly send you a email to have your opinion on it?
    thank you for helping us understanding this ic!


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