A piece of knowledge about switching power supply chips
Pulse Width Modulation (PWM), short for Pulse Width Modulation, is a highly effective technique for controlling analog circuits using digital outputs from microprocessors. It is widely used in many fields, from measurement and communication to power control and conversion.
The full English name of PFC is "Power Factor Correction", which means "power factor correction". Power factor refers to the relationship between effective power and total power consumption (apparent power), that is, the ratio of effective power to total power consumption (apparent power). Basically, power factor can measure the degree to which electricity is effectively utilized, and the larger the power factor value, the higher its electricity utilization rate.
Power supply (startup): The VDD pin of the chip is connected to a capacitor to ground and a resistor to the positive pole of the input voltage. When powered on, the input voltage charges the capacitor through the resistor. When the voltage on the capacitor reaches the startup voltage threshold of the chip, the chip starts working.
Power supply (maintenance): In order to save energy, the starting resistors are relatively large, and relying solely on resistors and capacitors cannot provide the current required to maintain the normal operation of the chip. Therefore, a power supply winding should be installed on the high-frequency transformer to supply power to the chip. Once the chip starts working, the output voltage of the winding provides continuous power to the chip.
Switch driver: Once the chip starts working, the GATE pin drives the switch to turn on or off, and each output winding outputs voltage.
Switch tube current detection: The source of the switch tube is connected to a current sampling resistor, and the sampled voltage is sent to the CS pin of the chip. When the current reaches the maximum design value, the CS pin voltage is greater than the reference voltage set inside the chip, and the GATE pin voltage decreases, turning off the switch tube.
Output voltage feedback: The change in output voltage is fed back to the COMP pin of the chip through the optocoupler, controlling the duty cycle.
