Output short circuit protection circuit

Abstract

An output short-circuit protection method is disclosed. The method comprises the steps of generating a low-level effective CS-Fault-L signal when a preprocessed CS port voltage detected by an overcurrent comparator is higher than a CS overvoltage threshold value Vref-OSP set in a controller; detecting the CS-Fault-L signal in each period; if the detected CS-Fault-L signal is always in low level detected in continuous several periods, transmitting the low-level signal to a logic module; enabling a low-voltage driving signal Drive-H of a driving tube to be low level and transmitting the low-level Drive-H signal to a driving module; enabling a grid electrode driving signal GATE of an output power tube to be low level, switching off the power tube and finishing the protection function. Compared with the prior art, the output short-circuit protection method can remove noise interference by filtration and avoid wrong switch-off of the controller; and meanwhile, the output short-circuit protection method is high in anti-interference capability and reliability, and capable of ensuring that the current stress applied to the power tube and a secondary side diode cannot damage the power tube and the secondary side diode within a timekeeping range, so that the output short-circuit protection method can be applied to a high-power switching power supply.

Description

technical field [0001] The invention relates to a switching power supply, in particular to an output short-circuit protection circuit of a switching power supply. Background technique [0002] Most of the current switching power supply control chips integrate some protection functions, such as output over-voltage protection, over-power protection, open-loop protection, output short-circuit protection and other common switching power supply protection functions. figure 1 It is a commonly used flyback switching power supply with feedback control on the secondary side. If the output short circuit occurs on the secondary side, the output current will increase greatly, causing the switching power supply itself to burn out due to excessive power consumption. Therefore, in order to solve the problem of output short circuit , Usually the controller has an output short-circuit protection function inside the controller. An existing controller, such as a PWM controller FAN6755W / FAN675...

AI Technical Summary

Problems solved by technology

[0005] 1. The controller that uses the FB pin as the output short-circuit protection function, when designing a high-power power supply, there is a risk that the power tube on the primary side will be under large stress and the rectifier diode on the secondary side will be under high stress, which may cause it to burn out;

[0006] 2. The controller that uses the CS pin as the output short-circuit protection function, the CS pin is easily affected by the signal from the external interference noise source, causing the controller to misjudge, and its anti-interference ability and reliability are poor

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