Synchronous rectification driving circuit of flyback converter

Abstract

The invention discloses a synchronous rectification driving circuit of a flyback converter. The synchronous rectification driving circuit comprises a synchronous rectification driving transformer, a coupling capacitor and a synchronous rectification driver, wherein the synchronous rectification driving transformer is a three-winding transformer; the input end of the synchronous rectification driver is connected with a pulse width modulation signal, and the output end of the synchronous rectification driver is connected to the like end of a primary winding of the synchronous rectification driving transformer by the coupling capacitor; the unlike ends of the primary winding and a first secondary winding of the synchronous rectification driving transformer are grounded; the like end of the first secondary winding of the synchronous rectification driving transformer outputs a signal for driving a switching tube in the flyback converter; the like end and unlike end of a second secondary winding of the synchronous rectification driving transformer output the signal for driving a synchronous rectification tube in the flyback converter; and the pulse width modulation signal controls the switching tube and the synchronous rectification tube in the flyback converter to be alternately switched on according to the duty ratio of the pulse width modulation signal by the synchronous rectification driving transformer.

Description

technical field [0001] The invention relates to a drive circuit, in particular to a synchronous rectification drive circuit of a flyback converter. Background technique [0002] In the field of switching power supplies, synchronous rectification technology has become one of the main key technologies for low-voltage and high-current DC / DC rectification. The output rectifier adopts MOSFET as synchronous rectifier, which can meet the requirements of the product on parameters such as efficiency, temperature rise, and noise, and can significantly reduce rectification loss, which is in line with the concept of energy saving and environmental protection. The single-ended flyback converter is the most widely used DC-DC conversion circuit topology. Because of its simple structure, reliable operation, and easy design and production, it is widely used in low-power applications. [0003] Such as figure 1 Shown is the circuit schematic diagram of the most widely used single-ended flyba...

AI Technical Summary

Problems solved by technology

The single-ended flyback converter includes a filter capacitor C1, a converter part composed of a switch tube Q1, a power transformer T1, and a synchronous rectifier tube Q2, and an output capacitor CL, which is driven by a synchronous rectification transformer T3, a coupling capacitor C2, and a synchronous rectification driver U2. Connect the drive circuit composed of PWM chip U1 and delay circuit U3; the gate of the switch tube Q1 is the input control terminal of the single-ended flyback converter, and receives high / low level signals to control the single-ended flyback converter energy storage / Cut-off; the gate and source of the synchronous rectifier Q2 are the output control terminals of the single-ended flyback converter, receiving high / low level signals to control the output / cut-off of the single-ended flyback converter; the pulse width modulation signal output by the PWM chip At the same time as the switching signal and driving signal of the switching tube Q1 and the synchronous rectification tube Q2, the pulse width modulation signal is amplified by the synchronous rectification driver U2, the coupling capacitor C2 is input into the synchronous rectification drive transformer T3, and the isolation coupling is output to the gate of the synchronous rectification tube Q2 and control the operation of the synchronous rectifier tube Q2, because the synchronous rectification drive transformer T3 will produce a certain delay, so the pulse width modulation signal output by the PWM chip U1 must first be properly delayed by the delay circuit U3 before driving the switch tube Q1; In this way, the phase of the waveform arriving at the synchronous rectifier tube Q2 and the waveform phase of the switching tube Q1 can be just reversed, which meets the requirements of the flyback converter for the timing of the drive signal of the switching tube and the synchronous rectifier tube; the disadvantage of this circuit is the delay of the delay circuit The timing needs to be adjusted according to the delay of the synchronous rectification drive transformer, and when the parameters are not set properly, it will affect the efficiency or reliability of the circuit

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