Pulse width modulation control circuit of AC/DC switch power supply

Abstract

The invention provides a pulse width modulation control circuit of an AC / DC switch power supply, which comprises a slope current drive circuit, a power NPN transistor and an output current detection circuit, wherein the slope current drive circuit is used for sampling the output current of the power NPN transistor and generating the base drive current of the power NPN transistor according to the output current of the power NPN transistor; the power NPN transistor is used for outputting the power; the output current detection circuit is used for detecting the transmitter current of the power NPN transistor. The pulse width modulation control circuit can prevent overhigh transmitter current to avoid causing damage to the power NPN transistor and can effectively improve the drive current andincrease the response speed.

Description

technical field [0001] The invention belongs to the field of analog integrated circuits, in particular to a pulse width modulation (PWM, Pulse Width Modulation) control circuit of an AC / DC switching power supply. Background technique [0002] In the prior art, the power switching tube of the switching power supply is connected to the transformer, and there will be a large surge voltage when the switch is turned off. If the power switching device is not selected properly, not only the conversion efficiency is low, but also breakdown phenomenon will occur, resulting Power failure. [0003] Active power devices commonly used in switching power supplies mainly include bipolar transistors (BJT), metal oxide power field effect transistors (MOSFETs), isolated gate bipolar transistors (IBGT) and silicon controlled transistors (SCR), etc., if Consider multiple BJT power transistors only in terms of cost and withstand voltage. But BJT also has some disadvantages at the same time. Wh...

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Problems solved by technology

But BJT also has some disadvantages at the same time. When BJT transitions from the saturation region to the cut-off region, the turn-off speed of the power bipolar transistor is slow due to the base storage effect; secondly, the BJT is a current-driven type, and its amplification when outputting a large current The multiple is small, and a large base drive current is required. Most of the drive circuits used today have a fixed drive current, resulting in a decrease in efficiency when the output power changes. At the same time, BJT has the possibility of secondary breakdown, so the safe operating range is reduced.

The current AC / DC switching power supply drivers use a large start-up resistor, and the start-up current is in the microampere level, so the start-up is slow

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