Synchronous rectification control method of flyback converter and its control module

Abstract

The invention particularly relates to a synchronous rectification control method for a flyback converter and a control module of the synchronous rectification control method. The synchronous rectification control method for the flyback converter is suitable for the flyback converter adopting a non-complementary active clamping control mode and mainly includes the following step of turn-off control, wherein a comparison difference value Vds is received, when the difference value Vds reflects that a current peak occurs when a first narrow pulse drive clamping tube is switched on once before a main switching tube is turned on, timekeeping is started, and a third narrow pulse Soff is transmitted when timekeeping duration reaches set duration; the step of driving, wherein a second narrow pulse and a third narrow pulse are received, switch-on, controlled by a rising edge of the second narrow pulse, of a synchronous rectification tube is output, and switch-off, controlled by a rising edge of the third narrow pulse, of the synchronous rectification tube is output. Compared with the prior art, the efficiency of the non-complementary active clamping control converter is improved further. It is unnecessary to use a synchronous transformer large in size for isolation, application is simple, and the synchronous rectification control method automatically adapts to a CCM working mode.

Description

technical field [0001] The invention relates to the field of switching converters, in particular to a synchronous rectification control method of a flyback converter and a control module thereof. Background technique [0002] With the rapid development of the field of power electronics, switching converters are used more and more widely, especially people put forward more requirements for switching converters with high power density, high reliability and small size. Generally, the traditional low-power AC / DC conversion is realized by the flyback topology, which has the advantages of simple structure and low cost; however, due to the influence of the leakage inductance of the transformer, the voltage clamping method of the main switching tube of the flyback converter includes RC buffer absorption , RCD clamp, LCD clamp and active clamp. The active clamp can not only absorb the energy of the leakage inductance and feed it back to the output terminal in the form of forward exc...

AI Technical Summary

Problems solved by technology

In the self-driving scheme, in a certain period of time, the oscillation caused by the leakage inductance of the transformer will affect the driving voltage and reduce the efficiency

At the same time, there is a delay in the drive circuit, and the synchronous rectifier SR also has a turn-on delay. When the shutdown signal is received, there is a delay until the synchronous rectifier SR is turned off, causing the output voltage to pass through the synchronization that has not been turned off in time. The rectifier tube SR supplies reverse power to the transformer winding or inductor to reduce efficiency, commonly known as reverse feeding

Backfeed not only reduces the efficiency, but also increases the voltage stress of the synchronous rectifier, thereby reducing the reliability of the device

[0016] The disadvantage of the external drive scheme is that the drive circuit is complex, detection control, timing logic, synchronous transformer, etc. are required, and currently there are very few synchronous rectification drive schemes that can adapt to CCM, which leads to non-complementary flyback active clamp converters Difficult to use external drive scheme

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