Synchronous rectification switching power supply and control circuit and control method thereof

Abstract

The invention discloses a synchronous rectification switching power supply and a control circuit and a control method thereof. The switching power supply comprises a transformer, a primary circuit, and a secondary switching tube, wherein the primary circuit is electrically coupled to a primary winding of the transformer; and the secondary switching tube is electrically coupled between a secondary winding of the transformer and a load. The synchronous rectification control circuit is electrically coupled to a grid of the secondary switching tube, and comprises an integrating circuit, a first comparison circuit and a logic circuit, wherein the integrating circuit is electrically coupled to the secondary winding of the transformer, and is used for integrating end voltage of the secondary winding to generate an integrated signal; the first comparison circuit is electrically coupled to the integrating circuit and is used for comparing the integrated signal with a first threshold value; and the logic circuit is electrically coupled to the first comparison circuit and is used for switching off the secondary switching tube according to a comparison result of the first comparison circuit. The integral value of the end voltage of the secondary winding is compared with the threshold value, and the secondary switching tube is switched off according to the comparison result, so that the secondary switching tube can be switched off before a primary switching tube is switched on, and direct connection is effectively avoided.

Description

technical field [0001] The invention relates to electronic circuits, in particular to a synchronous rectification switching power supply and its control circuit and control method. Background technique [0002] In recent years, the development of electronic technology has made the working voltage of the circuit lower and lower, and the current is higher and higher. Low-voltage operation is conducive to reducing the overall power consumption of the circuit, but it also poses new challenges to power supply design. [0003] The loss of the switching power supply is mainly composed of three parts: the loss of the power switch tube, the loss of the high-frequency transformer and the loss of the output rectifier tube. In the case of low voltage and high current output, the conduction voltage drop of the rectifier diode is relatively high, and the loss of the rectifier tube at the output end is particularly prominent. The turn-on voltage drop of fast recovery diode (FRD) or super...

AI Technical Summary

Problems solved by technology

If the turn-off delay is long, the secondary switch tube is still on after the secondary current drops to zero, and the primary switch tube and the secondary switch tube will be turned on at the same time (shoot through), causing damage to the switching power supply

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