Short-circuit protective circuit

Abstract

A short-circuit protecting circuit is composed of a time delay circuit for holding the sampled output current level of power unit for PWM switching power supply for a certain time and slowly lowering it to become a continuous signal, a short-circuit current threshold setting-up circuit for generating threshold level, an over-current detecting circuit for comparing the output of time delay circuit with the said threshold level and making judgement, and a lagging circuit for forming window comparactor, elongating short-circuit protecting signal, feeding the short-circuit protecting signal back to threshold setting up circuit, and improving the anti-interference power of over-current detecting circuit.

Description

technical field [0001] The invention relates to the field of switching power supplies, in particular to a current-type pulse width modulation (PWM) switching power supply. Background technique [0002] At present, the application of switching power supply is more and more extensive. In the protection function of switching power supply, a short circuit protection circuit is generally required to prevent the switching power supply from damaging the power supply and load due to excessive operating current when it is short-circuited. The performance of the short-circuit protection circuit directly affects the reliability of the entire power supply. At present, most of the short-circuit protection circuits in switching power supplies use the current peak limit circuit inside the pulse width modulation chip to detect the working current of the primary side of the transformer, and limit its peak value to achieve the function of short-circuit protection. Because this solution only ...

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Problems solved by technology

Since this solution only limits the current peak value of the main circuit, it has been frequently protected and restored in the short-circuit state, and the working current of the main circuit is still very large. There are problems such as high residual voltage of the short-circuit output of the switching power supply, large loss, and low reliability.

[0003] U.S. Patent US5,400,206 "Short circuit and overload protection circuit which allows a predetermined number of reconnection attempts" uses a short circuit protection circuit that can preset the number of short circuit recovery attempts, and uses a settable counter to limit the number of short circuit recovery attempts And time circuit, when the protection action exceeds a certain set number, the protection device is locked, and it is always in the protection state. This solution can solve the problem of large short-circuit loss of the switching power supply, but it cannot automatically recover after the short circuit is removed, and needs to be manually reset

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