Switching power supply on a single semiconductor with two operating modes
The monolithic switching power supply integrated circuit has the advantages of high integration, high cost performance, the simplest peripheral circuit, the best performance index, and can form a high-efficiency isolated switching power supply without power frequency transformer. After it came out in the mid-to-late 1990s, it has shown strong vitality. At present, it has become the preferred integrated circuit for the development of medium and small power switching power supplies, precision switching power supplies and power modules in the world. The switching power supply composed of it is equivalent in cost to the linear regulated power supply of the same power, while the power supply efficiency is significantly improved, and the volume and weight are greatly reduced. This has created good conditions for the promotion and popularization of new switching power supplies.
Features of monolithic switching power supply
(1)TOpSWitch-II includes oscillator, error amplifier, pulse width modulator, gate circuit, high voltage power switch tube (MOSFET), bias circuit, overcurrent protection circuit, overheat protection and power-on reset circuit, shutdown/ auto-restart circuit. It uses a high-frequency transformer to completely isolate the output terminal from the power grid, 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, which can be compared with three-terminal linear regulators, and can form a flyback switching power supply without a power frequency transformer in the simplest way. In order to complete a variety of control, bias and protection functions, C and D are multi-functional terminals, realizing one pin with multiple functions. Taking the control terminal as an example, it has three functions: ①The voltage VC of this terminal provides bias voltage for the on-chip shunt regulator and the gate driver stage; ②The current IC of this terminal can adjust the duty cycle; ③This terminal is also used as a power supply branch The connection point with the automatic restart/compensation capacitor, the frequency of the automatic restart is determined by an external bypass capacitor, and the control loop is compensated.
(3) The range of input AC voltage is extremely wide. 220V±15% AC power can be selected for fixed voltage input, if it is equipped with 85~265V wide-range AC power, 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 adjustment range of the duty ratio is 1.7% to 67%. The power supply efficiency is about 80%, up to 90%, which is nearly double that of the linear integrated regulated power supply. Its working temperature range is 0～70℃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 ratio D to achieve the purpose of voltage regulation. For example, when the output voltage VOT of the switching power supply is caused by some reason, the optocoupler feedback circuit will make Ic↑→error voltage Vrt→D↓→Vo↓, so that Vo remains unchanged. vice versa.
(6) The peripheral circuit is simple and the cost is low. Externally only need to connect rectification filter, high frequency transformer, primary protection circuit, feedback circuit and output circuit. The use of such chips can also reduce electromagnetic interference generated by switching power supplies.
