Active clamp flyback power converter and related control method

Abstract

An active clamp flyback power converter includes an active clamp circuit in parallel with a main winding of a transformer. The active clamp circuit comprises an upper arm switch and a capacitor whichare connected in series. The active clamp flyback power converter includes a lower arm switch connecting the main winding to a first power line. The control method comprises the steps: the lower arm switch is switched to generate N continuous switching periods, wherein N is an integer larger than 1, at least the Nth switching period is an improved flyback period, and the other switching periods are normal flyback periods; each switching period is made not less than the shielding time, wherein the shielding time is generated according to the load of the active clamp flyback power converter; ineach normal flyback period, the upper arm switch is fixedly maintained to be turned off; and in each improved flyback period, after the shielding time, the upper arm switch is turned on to generate anupper arm turn-on time, so that the lower arm switch performs zero-voltage switching.

Description

technical field [0001] The present invention generally relates to active clamp flyback power converters and related control methods, and more particularly to the related art of active clamp flyback power converters that can have active clamp circuits without energy loss. Background technique [0002] Flyback power converters have been widely used in power supplies of many electronic products, such as home appliances, computers, battery chargers, and so on. In order to improve the power conversion efficiency, an active-clamp circuit is used to improve the energy loss problem of the snubber of the general flyback power converter. Generally, a flyback power converter with an active clamp circuit is called an active clamp flyback (ACF) power converter. Under heavy load conditions, ACF power converters tend to excel in power conversion performance. However, under light load conditions, the ACF power converter often has high power loss due to the circulating current in the main ...

AI Technical Summary

Problems solved by technology

Because of the existence of the bleeder resistor, the active clamp circuit provided by Texas Instruments still has energy loss

[0004] Moreover, conventional ACF power converters often suffer from electromagnetic interference (EMI) and / or audible noise in system design.

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