Control circuit and control method of flyback convertor and alternating current-direct current power converting circuit applying control circuit of flyback convertor

Abstract

The invention relates to a control circuit and a control method of a flyback convertor and an alternating current-direct current power converting circuit applying the control circuit of the flyback convertor. Within each switch period, an opening signal generating circuit is used for receiving drain-source voltage of a power switch in the flyback converter; when the drain-source voltage reaches valley value, opening signal is generated to control the turn-on of the power switch; a turn-off signal generating circuit is used for generating a turn-off signal after the power switch turns on and a turn-on time interval is completed according to a feedback error signal of a received output electric signal for representing the flyback converter; and the turn-off signal controls the power switch to turn off, so as to lead input current and input voltage of the flyback converter in a same phase and keep the output electric signal of the flyback converter constant.

Description

technical field [0001] The present invention relates to the field of power supplies, more specifically, to a control circuit and control method of a flyback converter and an AC-DC power conversion circuit using the same. Background technique [0002] Active power factor correction (active power factor correction, APFC) is an important way to use electric energy efficiently and with low pollution. It adds a power conversion circuit between the bridge rectifier and the output capacitor filter to make the power factor close to 1. The active power factor correction circuit works in a high-frequency switching state, has the characteristics of small size, light weight, high efficiency, etc., and has become a new hot spot in the research of power electronics technology. [0003] In the prior art, power factor correction technology is widely used in off-line switching power supplies. Most of the existing switching power supplies with power factor correction function include a two-s...

AI Technical Summary

Problems solved by technology

[0007] It can be seen that the power factor correction implementation scheme of the prior art needs to adopt a two-stage power conversion circuit, which obviously increases the cost and size of the circuit; in addition, the implementation scheme of the power factor correction of the prior art needs to sample the input voltage, and through analog multiplication The device receives the input voltage to obtain a sine half-wave signal that the inductor current must follow compulsively. Such an implementation scheme is complicated; and for integrated circuits, a separate pin is bound to be required to receive the input voltage, which is not conducive to the chip The miniaturization and package design of the

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