Flyback control circuit and control method

Abstract

The invention particularly relates to a control circuit and a control method of a flyback active clamp and an asymmetrical half-bridge switching converter. As far as the circuit solution is concerned, the present invention provides a flyback control circuit, including an integrated control circuit for controlling the switch tube and the clamp tube, and the integrated control circuit includes a drive unit for the switch tube, a drive unit for the clamp tube, and an off-hold drive When the unit is light-loaded or no-loaded, the sum of the turn-on time of the switch tube, the turn-on time of the clamp tube and the dead time between them forms a single cycle, and the duration of the single cycle is a fixed value. The turn-on time of the switch tube It has a complementary relationship with the turn-on time of the clamp tube in a single cycle; the time of a single cycle and the time of keeping it off constitute the total working cycle. Compared with the prior art, the present invention improves light-load efficiency and reduces no-load power consumption under the condition of ensuring the efficiency and EMI advantages of traditional circuits under light-load and above loads.

Description

technical field [0001] The invention relates to the field of switching converters, in particular to a control circuit and a control method of flyback active clamping and asymmetrical half-bridge switching converters. 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, traditional low-power AC / DC converters are implemented using flyback topology, which has the advantages of simple structure and low cost; however, ordinary flyback topology is a hard switch, and cannot recover leakage inductance energy, thus limiting the efficiency of small and medium power products And volume, in order to meet the development trend of miniaturization, light weight and modularization of power converters, soft switching technology has become one of the hot spots in ...

AI Technical Summary

Problems solved by technology

[0004] The loss sources of its large no-load power consumption and low light-load efficiency are mainly: 1. The peak current is large and the effective value of the current is large, which causes large turn-off loss and winding loss; 2. The high switching frequency further increases the turn-off loss, and at the same time The iron loss of the magnetic core is also very large

The peak current is large because the duty cycle of this type of complementary working topology is almost constant under no-load and full-load conditions, so the peak current will be relatively large. At the same time, it cannot be directly Reduce the frequency, which will cause the excitation time to be too long to saturate the transformer and break down the switch tube

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