Quasi-resonant controlling and driving circuit and method for a flyback converter

摘要

The present invention relates to a quasi-resonant controlling and driving circuit and method for a flyback converter. In one embodiment, a controlling and driving circuit for a flyback converter, can include: a differentiation circuit configured to receive a third controlling signal and a drain-source voltage of a main power switch of the flyback converter; where the drain-source voltage is configured to be differentiated by the differentiation circuit to generate a differential voltage when the third controlling signal is active within an interval that the main power switch is shut-off; a valley voltage detection circuit coupled to the differentiation circuit, and configured to receive the differential voltage; and where a valley controlling signal is configured to be generated by the valley voltage detection circuit to achieve quasi-resonant driving for the main power switch of the flyback converter when the differential voltage crosses zero with a positive slope.

主权项

1. A controlling and driving circuit for a flyback converter, the controlling and driving circuit comprising:
a) a differentiation circuit configured to receive a third controlling signal and a drain-source voltage of a main power switch of said flyback converter, wherein said drain-source voltage is configured to be differentiated by said differentiation circuit to generate a differential voltage when said third controlling signal is active within an interval that said main power switch is shut-off; b) a valley voltage detection circuit coupled to said differentiation circuit, said valley voltage detection circuit being configured to receive said differential voltage, and to generate a valley controlling signal to achieve quasi-resonant driving for said main power switch of said flyback converter when said differential voltage crosses zero with a positive slope; and c) said differentiation circuit comprising an enabling circuit configured to receive said third controlling signal, a differentiation capacitor and a differentiation resistor coupled between a drain of said main power switch and ground, wherein a common node of said differentiation capacitor and said differentiation resistor is coupled to a controlling terminal of said main power switch, and wherein said enabling circuit is configured to enable said differentiation capacitor and said differentiation resistor to differentiate said drain-source voltage when said third controlling signal is active.