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.
Types of PWM controllers
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:
- 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.
- 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.
- 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.
- Pure sine wave inverter A-Z
- How to use MOSFET DRIVER 1R2110.
- DC-DC converter using push pull topology
- how to make H bridge and diagnose problems
- SPWM generation using PIC16F877A microcontroller
- Complete circuit diagram of pure sine wave inveter and coding
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 🙂