Characteristics of single-chip switching power supply
(1)TOpSWitch-II includes an oscillator, an error amplifier, a pulse width modulator, a gate circuit, a high-voltage power switch tube (MOSFET), a bias circuit, an overcurrent protection circuit, an overheat protection and power-on reset circuit, and a shutdown/automatic restart circuit. It completely isolates the output terminal from the power grid through a high-frequency transformer, which is safe to use. It belongs to the current-controlled switching power supply with open drain output. Because of the CMOS circuit, the power consumption of the device is significantly reduced.
(2) There are only three terminals: the control terminal C, the source terminal S and the drain terminal D, which are comparable to the three-terminal linear regulator 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 all multi-functional terminals, realizing multi-purpose with one foot. Taking the control terminal as an example, it has three functions: ① the terminal voltage VC provides bias 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 is also used as the connection point between the power supply branch and the automatic restart/compensation capacitor. The frequency of automatic restart is determined by the external bypass capacitor, and the control loop is compensated.
(3) The range of input AC voltage is extremely wide. 220 V 15% AC can be selected for fixed voltage input, and the maximum output power will be reduced by 40% if 85~265V AC is used. The input frequency range of switching power supply is 47~440Hz.
(4) The typical switching frequency is 100KHz, and the duty cycle adjustment range is 1.7% ~ 67%. The efficiency of power supply is about 80%, and the highest can reach 90%, which is nearly double that of linear integrated regulated power supply. Its working temperature range is 0 ~ 70℃, and the highest junction temperature of the chip Tjm=135℃.
(5) The basic working principle of 5)TOpSwitch-II is to use feedback current IC to adjust the duty ratio D to achieve the purpose of voltage stabilization. For example, when the output voltage VoT of the switching power supply is caused for some reason, Ic↑→ error voltage VRT → D → VO ↓ will be kept unchanged through the optocoupler feedback circuit. or vice versa, Dallas to the auditorium
(6) The peripheral circuit is simple and the cost is low. External only needs to be connected with rectifier filter, high-frequency transformer, primary protection circuit, feedback circuit and output circuit. Using this kind of chip can also reduce the electromagnetic interference generated by switching power supply.
