Characteristics of monolithic switching power supply
(1)TOpSWitch-II internally includes an oscillator, error amplifier, pulse width modulator, gate circuit, high-voltage power switch tube (MOSFET), bias circuit, overcurrent protection circuit, overheating protection and power-on reset circuit, shutdown/ Automatic restart circuit. It completely isolates the output end from the power grid through a high-frequency transformer, making it safe and reliable to use. It is a current-controlled switching power supply with open-drain output. Due to the use of CMOS circuits, the power consumption of the device is significantly reduced.
(2) There are only three terminals: control terminal C, source S, and drain D. It is comparable to a three-terminal linear regulator and can constitute a flyback switching power supply without a power frequency transformer in the simplest way. In order to complete various control, bias and protection functions, C and D are multi-functional terminals, realizing one pin for multiple purposes. Taking the control terminal as an example, it has three functions: ① The voltage VC at this terminal provides bias voltage for the on-chip parallel regulator and gate driver stage; ② The current IC at this terminal can adjust the duty cycle; ③ This terminal also serves as a power branch The connection point with the automatic restart/compensation capacitor determines the frequency of automatic restart through an external bypass capacitor and compensates the control loop.
(3) The input AC voltage range is extremely wide. For fixed voltage input, 220V±15% AC power can be selected. If it is equipped with AC power with a wide range of 85~265V, the maximum output power will be reduced by 40%. The input frequency range of the switching power supply is 47~440Hz.
(4) The typical value of the switching frequency is 100KHz, and the duty cycle adjustment range is 1.7% to 67%. The power efficiency is about 80% and can reach up to 90%, which is nearly twice as high as the linear integrated regulated power supply. Its operating temperature range is 0~70℃, and the maximum junction temperature of the chip is Tjm=135℃.
(5) The basic working principle of TOpSwitch-II is to use the feedback current IC to adjust the duty cycle D to achieve voltage stabilization. For example, when the output voltage VOT of the switching power supply is caused for some reason, the optocoupler feedback circuit makes Ic↑→error voltage Vrt→D↓→Vo↓, keeping Vo unchanged. vice versa.
(6) The peripheral circuit is simple and low cost. Only the external rectifier filter, high-frequency transformer, primary protection circuit, feedback circuit and output circuit are needed. The use of such chips can also reduce electromagnetic interference generated by switching power supplies.
