TOP2XX series IC is one kind will control circuit and power switch compositive the chip of power source of 3 upright switch that be together. Of this kind of chip enclose a form to be TO-220, if pin name and function pursue (A) place is shown, their interior sets MOSFET of amplifier of comparator of oscillator, PWM, error, logistic circuit, tall compression to output switch canal and current limliting, owe press a lock calm circuit and press too, temperature protects circuit. Change infuse foot of control pole C(1) electric current can control what MOSFET switch outputs inside chip to occupy sky comparing. Graph (B) place shows the representative application circuit that is TOP204. The technical characteristic of this power source is input voltage to communicate 85 ～ 265V; Output voltage is 15V±2 ％ ; Rated output power is 30W; Output voltage ripple is not more than ±50mV; Linear regulation is ±2 ％ ; Efficiency is 85 ％ . In circuit, make circuit of output voltage sampling by R4 of ～ of N3, D8, C7, IC2, IC3, R1 and C8, control what IC1 outputs pulse to occupy sky comparing, realize stability to output the purpose of voltage thereby.