Switching power supply made of TOP204 switching power supply IC

TOP2XX series IC is a kind of three-terminal switch power supply chip that integrates control circuit and power switch. The package form of this kind of chip is TO-220. The pin name and function are shown in Figure (a). They are equipped with oscillators, PWM comparators, error amplifiers, logic circuits, high-voltage MOSFET output switch tubes, current limiting, undervoltage lockout circuits, and overvoltage and temperature protection circuits. The duty cycle of the output MOSFET switch in the chip can be controlled by changing the current injected into the control electrode C (pin 1). Figure (b) shows the typical application circuit of TOP204. The technical characteristics of this power supply are input voltage of AC 85~265V; output voltage of 15V±2%; rated output power of 30W; output voltage ripple is not more than ±50mV; linear regulation rate is ±2%; efficiency is 85%. In the circuit, N3, D8, C7, IC2, IC3, R1~R4 and C8 constitute the output voltage sampling circuit to control the duty cycle of IC1 output pulse, thereby achieving the purpose of stabilizing the output voltage.