Switching power supply based on UC3842

A high frequency single-ended flyback switching power supply is designed with current-mode PWM controller UC3842 chip as its core.Based on the signal flow and functional circuit modules,the voltage control and stable output are realized by using three-terminal voltage regulator TL431 with the new device UC3842.Its design principle,module functions and working process are analyzed.In order to meet the requirements of electromagnetic compatibility and safety,the low-pass filter is used to restrain the conducted interference,and the optical coupler PC817 is used to realize the input /output isolation and feedback.The over-voltage and over-current protective measures are taken and the thermistor and varistor are added in power supply circuitry.Test results show that the designed power supply has good voltage regulation performance,with small ripple and high regulation rate of voltage and load.