Self-driving circuit of antilaser converter synchronous rectifier

Abstract

The auto drive circuit is composed of a delay drive circuit, which delays the PWM signal and transmits it to the gate level of the master power transistor; a separating differential circuit, which imports the PWM signal and export the narrow pulse signal; a synchronized rectifier disconnection triggering circuit, which receives the narrow pulse signal and disconnects the synchronized rectifier; and a synchronized rectifier with the auto lock and driving maintaining circuit.

Description

technical field [0001] The invention relates to a switching power supply, in particular to a novel self-driving circuit for a synchronous rectifier tube of a flyback converter. Background technique [0002] The traditional synchronous rectification self-driving circuit of the flyback converter cannot control the common conduction well, so it cannot obtain high efficiency. figure 1 The traditional self-driving technique shown is to use an external auxiliary winding Nb to drive the synchronous rectifier S3. When S1 is turned off, the voltage of the secondary winding Ns and the driving winding Nb becomes positive and negative, S3 is turned on, and the energy of the secondary side of the transformer is provided to the load through S3; when S1 is turned on, the voltage of the secondary winding Ns and Nb becomes The process of up-negative and down-positive takes time, so that S1 and S3 are turned on together, and the secondary side is short-circuited. Alt...

AI Technical Summary

Problems solved by technology

Although the solution figure 1 The disadvantages of the middle scheme have greatly improved the efficiency of the converter, but this self-driving circuit transmits the entire PWM signal to the secondary side to realize the turn-off and turn-on of the synchronous rectifier tube, and the isolation drive transformer needs to transmit power, so , the volume of the isolation drive transformer is difficult to make small

In occasions where primary and secondary side high-voltage isolation is required, the volume of the isolation drive transformer will be larger due to the requirement of safety distance

At the same time, in this case, due to the large leakage inductance of the driving transformer, the driving waveform transmitted to the secondary side has a large voltage spike, which is likely to break down the gate-source of the synchronous rectifier.

This makes it difficult for this self-driven circuit to achieve high power density, and it is not suitable for occasions where high voltage isolation is required for the primary and secondary sides

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