Flyback control circuit and control method

Abstract

The invention in particular relates to a flyback active-clamp, asymmetrical half-bridge switching converter control circuit and control method. According to the technical scheme of the circuit, a flyback control circuit is provided and controls an integrated control circuit controlling a switch tube and a clamping tube. The integrated control circuit comprises a driving unit of the switch tube, a driving unit of the clamping tube, and a turn-off holding driving unit. When the load is light or zero, the total of a turn-on time of the switch tube, a turn-on time of the clamping tube and a dead zone therebetween forms a single period. The time length of the single period is a fixed value. The turn-on time of the switch tube and that of the clamping tube are in a complementary relation in the single period. The time of the single period and a turn-off holding time form a total working period. Compared with the prior art, while ensuring the efficiency of a conventional circuit and the EMI advantage under a load no less than a light load, the circuit improves the light load efficiency and reduces the zero load power consumption.

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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