Collection of problems encountered in switching power supplies and corresponding solutions (4)

Project: 431 plus photocoupler feedback flyback

Phenomenon: The output voltage regulation rate is very poor, and the voltage drops significantly as the load increases. The voltage difference between the measured voltage sampling point and the output pin is not large.

Solution: Connect a small capacitor between the reference pin and the cathode of the 431. The regulation rate will improve immediately.

Analysis: The reference foot of 431 is disturbed.

Project: IR1150 boost PFC

Phenomenon: The switching power supply frequency is 100K, but the input has a 1Khz ripple current. The X capacitor also squeaks.

Solution: Adjust the EMI filter parameters.

Analysis: The EMI filter resonates itself.

Project: Flyback Synchronous Rectification

Phenomenon: The voltage spike of the synchronous rectifier is very high and cannot be absorbed.

Solution: Replace the synchronous tube with a tube with a fast recovery body diode

Analysis: Since the reverse recovery time of the synchronous tube's body diode is too long, it leads to a large reverse recovery current, which causes a severe voltage spike.