A synchronous rectification circuit and method

Abstract

The invention discloses a synchronous rectification circuit and method. The current signal of a synchronous rectification MOSFET is converted into a voltage signal to be output to a signal amplifyingcircuit; when the output signal of the signal amplifying circuit is greater than the positive threshold voltage of a hysteresis comparator circuit, the hysteresis comparator circuit outputs saturatedpositive voltage so that the synchronous rectification MOSFET is switched on, when the output signal of the signal amplifying circuit is smaller than a negative threshold voltage, saturated negative voltage is output so that the synchronous rectification MOSFET is switched off; the input end of an optocoupler isolation circuit is connected to the output end of a primary side PWM controller, when aPWM signal output at the output end of the primary side PWM controller is saturated positive voltage, the optocoupler isolation circuit outputs saturated negative voltage so that the synchronous rectification MOSFET is switched off, when the PWM signal output at the output end of the primary side PWM controller is saturated negative voltage, the synchronous rectification MOSFET is used for turning off a control circuit to be output in a high resistance state, and simultaneously, the switching-on and switching-off of the synchronous rectification MOSFET is decided by the output voltage of thehysteresis comparator circuit, and the synchronous rectification MOSFET remains in a turn-off state when the PWM signal output at the output end of the primary side PWM controller is saturated positive voltage.

Description

technical field [0001] The invention relates to the field of switching power supplies, in particular to a synchronous rectification circuit and method. Background technique [0002] With the development of electronic technology, electronic systems have higher and higher requirements for power supply, and high-efficiency, high-performance switching power supply technology has been more and more widely used. Traditional isolated switching power supplies mostly use diodes for secondary side rectification, such as figure 1 shown. Since the diode itself has a certain tube voltage drop, when the secondary side current is large, a large power loss will be generated, which makes it difficult to improve the efficiency of the power supply. [0003] In order to solve the problem of large diode loss, synchronous rectification technology has been widely studied and applied in recent years. MOSFETs are used instead of diodes for rectification. Since the conduction loss of MOSFETs is muc...

AI Technical Summary

Problems solved by technology

This existing synchronous rectification circuit is simple, but in actual power supply products, due to the existence of non-ideal factors such as transformer leakage inductance and parasitic inductance and parasitic capacitance, the voltage at both ends of the secondary winding of the transformer will oscillate, thereby affecting the synchronous rectification. The control of the MOSFET can easily cause the wrong turn-on of the synchronous rectification MOSFET and then damage the power supply or affect the efficiency of the power supply

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