SG3525 PWM IC Characteristics, Internal Structure, Working Principle and SG3525 vs SG3524
03 April 2024
Ⅲ. Internal structure and working principle of SG3525
Ⅳ. Representative block diagram of SG3525
Ⅴ. Application circuit of SG3525
Ⅵ. How to adjust the frequency of SG3525?
Ⅶ. The main differences between SG3525 and SG3524
With the development of power conversion technology, power MOSEET has begun to be widely used in switching converters. SG3525 is used to drive N-channel power MOSEET, which is widely used in industrial automation, electric vehicles, solar panels and wind power generation systems. Through this article, we can have an in-depth understanding of the characteristics, internal structure and working principle of SG3525, so that you can have a deep understanding of this device. So let’s get started!
SG3525 is a monolithic integrated PWM control chip with excellent performance, complete functions and strong versatility. It is simple and reliable, easy to use and flexible, and adopts push-pull output form of output drive, thereby enhancing the drive capability. The chip integrates an undervoltage lockout circuit, a soft-start control circuit and a PWM latch, and has an overcurrent protection function. In addition, its frequency is adjustable and the maximum duty cycle can be limited. The SG3525 can operate stably over a supply voltage range of 8 to 35 volts. At the same time, it also provides multi-functional dead time control function between switching signals to turn on or off devices such as MOSFETs, IGBTs and power transistors.
Alternative models:
• KA3525A
• KA7500
• SG1525AJ
• TL494
SG3525 has the following features:
1. Good linear performance: The output of SG3525 has good linear performance and is an ideal switching power supply controller.
2. High accuracy: SG3525 provides a voltage reference source with an accuracy of up to one percent to ensure output stability.
3. Wide input voltage range: The input voltage range of SG3525 is 8V to 35V. This wide range makes it suitable for many different applications.
4. Large output drive capability: The output terminal of SG3525 has a current drive capability of up to 200mA, which can directly drive power transistors or MOSFETs.
5. Adjustable frequency: The output frequency of SG3525 can be adjusted through an external RC network, and its frequency range covers 100Hz to 400kHz, thus meeting the needs of different applications.
1. Internal structure of SG3525
The entire circuit of SG3525 consists of an output stage, an out-of-phase oscillator, a comparison amplifier, a double D flip-flop, an error amplifier and a control logic circuit. Its main components include:
(1) Output stage: The output stage is responsible for driving the switching tube, converting the pulse signal generated by the control logic circuit into a high voltage and high current square wave signal to drive the load.
(2) Out-of-phase oscillator: SG3525 integrates an out-of-phase oscillator circuit to generate a set of complementary triangle wave signals. These complementary signals are used to compare the input of the amplifier to the reference voltage of the error amplifier.
(3) Double D flip-flop: Double D flip-flop is used for delay control. By changing the size of the delay capacitor, the frequency of the output waveform can be adjusted. Double D flip-flops can also be used to generate pulse signals to control the on and off of switching tubes.
(4) Comparison amplifier: The comparison amplifier receives the output signal of the error amplifier and compares it with the output signal of the triangle wave oscillator. By controlling the input signal of the comparison amplifier, the pulse width of the output waveform can be adjusted.
(5) Error amplifier: The error amplifier compares the input voltage and the output voltage, and adjusts the output voltage by increasing or decreasing the input voltage. It efficiently converts the input voltage into a pulse width control signal.
(6) Control logic circuit: The control logic circuit is a combinational logic circuit that regulates the pulse width and frequency of the output waveform based on the input control signal. In addition, the circuit also has an overload protection function. Once the output waveform exceeds the set limit, the output will be automatically cut off to ensure safe and stable operation of the circuit.
2. Working principle of SG3525
After the input voltage has been reduced and filtered, it will be sent to the SG3525. First, the feedback signal is compared with the reference signal in a comparator to generate an error signal. Subsequently, the phase-locked loop will synchronize this error signal to the clock signal and control the on-time of the switch tube accordingly. Finally, the output stage will be responsible for controlling the on and off of the switch tube, thereby achieving effective control of the output voltage or current.
1. Electric vehicle charger
SG3525 can be used as the controller of an electric vehicle charger to realize the charging function of electric vehicles by adjusting the input voltage and current. In this circuit, SG3525 is responsible for controlling the switching time and duty cycle of the power switch tube to adjust the output voltage and current to ensure fast and safe charging of the electric vehicle battery.
2. Switching power supply circuit
SG3525 can be used as a PWM controller to realize the design of switching power supply. In this circuit, we first step down the input voltage through a transformer, and then obtain the DC voltage through a rectifier circuit. Then, SG3525 is used to control the switching time and duty cycle of the power switch tube to achieve stable regulation of the output voltage.
3. Inverter circuit
Inverter is used to convert DC voltage into AC voltage. SG3525 can realize inverter designs with different output frequencies and voltages by adjusting the frequency and duty cycle of its pins. In this circuit, SG3525 is used to control the power switch to drive the transformer, thereby converting DC voltage into a variety of different AC voltages.
The frequency of SG3525 is realized by adjusting the sawtooth wave frequency of its internal oscillator. The frequency of each PWM is half of the sawtooth wave frequency. Specifically, we can adjust the frequency by changing the current size of pin 6, which is actually equivalent to changing the size of the internal resistor RT. According to the relevant formula, changing the size of RT can adjust the frequency of the control signal output by SG3525. In addition, SG3525 also has a soft-start function, which is also realized by adjusting the load operating frequency. During the soft-start process, the frequency of the control signal can be gradually adjusted by changing the current size of pin 6, thus realizing the smooth startup of the power supply.
Based on SG3524, SG3525 mainly makes the following improvements.
1. The comparator of SG3524 originally has two inverting input terminals, among which the three signals of error amplifier, current controller and shutdown control share one inverting input terminal. Now after improvement, an inverting input terminal is added, so that the error amplifier and the shutdown circuit can be sent to the inverting terminal of the comparator respectively. Such changes avoid the mutual influence between them, thereby helping to improve the working accuracy of the error amplifier and compensation network.
2. The main function of adding an undervoltage lockout circuit is: when the IC input voltage is lower than 8V, the internal circuit of the integrated block will lock and stop working (except for the reference source and necessary circuits), thereby reducing its current consumption to about 2mA.
3. The inverting end of the comparator of the soft start circuit, that is, the soft start control terminal pin 8, can be connected to an external soft start capacitor. The capacitor is charged by a 50μA constant current source with an internal 5V reference voltage, causing the duty cycle to change from small to large.
4. Adding a PWM latch makes the shutdown function more reliable. The output of the comparator (pulse width modulation) is fed to the PWM latch, which is set by the shutdown circuit and reset by the time pulse output by the oscillator. Therefore, when the shutdown circuit operates, even if the overcurrent signal disappears immediately, the latch can maintain shutdown control for one cycle until the clock signal of the next cycle resets the latch.
Frequently Asked Questions
1. What is SG3525 inverter?
SG3525 can control the output voltage of the inverter. It is also useful in driving MOSFET IRF520 connected to a transformer. Both MOSFET is used as a low-side connection. The SG3525 has a built-in Totem Pole Circuit to drive low-side connected MOSFETs.
2. What is the function of SG3525?
SG3525 is mainly used in DC-DC inverters. It is used for regulating the power supply. It is used in the switching regulators of any polarity.
3. How do you test a circuit with SG3525?
To test it, connect any load such as Bulb, CFL, or AC Fan at the output of the transformer. The bulb glows and Fan turns on immediately. You may try some other load with a higher power rating. Using the multimeter, you may test the voltage at the input and the output.
4. What is the compensation pin for SG3525?
Pin 9 is compensation. It may be used in conjunction with pin 1 to provide feedback compensation. Now that we've seen the function of each pin, let's design a circuit with the SG3525 and see how it is put to use practically.
