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 frequency increases with the increase in load.But Pulse frequency modulation technique cause 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 pulse or on time increase with the increase in load. Pulse width modulation also resolve the issues which occurs in Pulse frequency modulation. Therefore, Pulse width modulation is preferred technique for control circuits of switch mode power supplies.

There are many PWM ( Pulse width modulation ) controller integrated circuits  available in the market which 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:

Voltage control method used a feedback voltage by comparing it with reference value to set duty cycle of PWM. In return to control output voltage of SMPS. While current control method use Output current from output inductor to compare it with the reference value and to set the duty cycle of PWM. I have used 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 are complement of each other.
  • It is used to generate PWM signal for power electronics projects and also for switch mode power supplies.
  • It offers feedback circuitry to control output voltage by comparing feedback signal with reference voltage.
  • It has a protection circuitry which shutdown the PWM signal based on feedback current limit.

Features of SG3525

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

How to use SG3525

  • Sg3525 is a voltage mode PWM  controller integrated circuit. It is used in maximum inverters available in 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 have two PWM outputs both are inversion of each.Another advantage of  SG3525 is that it has 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 semi conductor devices upto current range of 50mA. For example, if you are using a switch which requires more than 50mA to operate, then you will have to use driver IC like MOSFET driver IR2110.
  • Description and functionality of each pin is given in next section on pinout of sg3525.

Pinout with functionality of each pin

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

SG3525
SG3525_pin
  • Pin 1 is a inverting pin and pin 2 is a non inverting pin.If the voltage on inverting pin is greater than voltage on non inverting pin, duty cycle increases and  if voltage on non inverting pin is greater than inverting pin , duty cycle decreases. So you can use one pin for feed back through voltage divider and one pin for setting of reference voltage.
  • pin 3 is used for synchronization of two waves.
  • pin 4 is output of oscillator.
  • pin 5, 6 and 7 is used to set frequency of PWM. Frequency can be calculated by using following formula:

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

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

  • Pin 8 SS is a 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 from 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 volt it will remain in shut down mode.
  • pin 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 have 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 to give 5 volt to shut down pin in case you want to shut down sg3525 through push button.

Circuit diagram to generate PWM

Diagrams below shows the circuit diagram of sg3525 which generate two inverted PWM signals.

sg3525_circuit
sg3525_circuit
output of sg3525
output of sg3525
  • In above circuit diagram feedback from the output is used to get regulated voltage.
  • It is  discussed in detail in Dc to dc converter using push-pull topology part.

Applications

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

Other articles of pure sine wave inverter.

Comment your problems on this post.  I will try to answer to your comments as soon as possible. Don’t forget to share  this article  with your friends.Good luck with your circuit 🙂

139 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 ?
    50kHz
    150 -200 watt
    output voltage 330v of transformer
    input voltage 10 -12.5

  2. 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.

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

  4. 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:
    ID: [email protected]

  5. 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 [email protected].
    Thanks very much!

  6. 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

  7. 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 [email protected]
    one more question does SG3525A IC is same as KA3525A IC ?

  8. 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

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