A zero-crossing detection circuit and switching power supply

Abstract

The present application provides a zero-crossing detection circuit of a switching power supply and a switching power supply. The zero-crossing detection circuit includes a state judgment circuit, an adjustment voltage generation circuit and a first comparison circuit. During the working process of the zero-crossing detection circuit, the state judging circuit judges whether the body diode of the synchronous tube is conducting when the synchronous tube is turned off, and according to the judgment result, the adjustment voltage generation circuit generates a Through the adjustment voltage of the state change, and then the detection voltage formed by superimposing the adjustment voltage and the voltage at the first end of the synchronous tube is compared with the voltage at the second end of the synchronous tube by the first comparison circuit to output a zero-crossing detection signal. Therefore, under different output voltage states of the switching power supply, the zero-crossing detection circuit can control the synchronous tube to be turned off while the inductor current is near zero, which can effectively reduce the power consumption of the switching power supply and improve the efficiency of the switching power supply.

Description

technical field [0001] The invention relates to a power electronic technology, in particular to a zero-crossing detection circuit and a switching power supply. Background technique [0002] In a synchronous switching power supply, under light load conditions, the synchronous tube needs to be turned off when the inductor current gradually drops to zero during the freewheeling process of the synchronous tube to reduce power consumption and improve efficiency. The operating mode of the inductor current in this process is discontinuous conduction mode (DCM). [0003] In discontinuous conduction mode, a zero-crossing detection circuit is required to detect whether the inductor current crosses zero. figure 1 A zero-crossing detection circuit for a step-down synchronous switching power supply realized in the prior art, the detection circuit adopts a series connection of a switching tube SD and a synchronous switching tube SW, and the connected node LX is the switching node of the ...

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Problems solved by technology

[0005] In view of this, the present invention provides a zero-crossing detection circuit of a switching power supply and a switching power supply to solve the problem that the synchronous tube cannot be precisely controlled to be turned off when the inductor current crosses zero due to the difference in the output voltage of the switching power supply in the prior art. Broken question

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