FLYBACK CONVERTER, CONTROL CIRCUIT AND CONTROL METHOD THEREFOR

摘要

The disclosure relates to a flyback converter, a control circuit and a control method therefor. In the control method, a power stage circuit is controlled at a light load to operate alternatively in a pulse width modulation mode (i.e. a constant switching frequency mode) and in a constant on time mode, in accordance with a voltage compensation signal. Thus, output energy may decrease rapidly and smoothly, without need for the control circuit to stop working. The flyback converter has increased efficiency at the light load and decreased output voltage ripple.

主权项

1. A control circuit for controlling a power stage circuit of a flyback converter at a light load, comprising:
a compensation circuit configured to generate a voltage compensation signal which represents a difference between an output voltage of said power stage circuit and a reference voltage; and a control signal generating circuit configured to generate a switching control signal in a pulse width modulation mode in a case that said voltage compensation signal is within a first range, and to generate a switching control signal in a constant on time mode in a case that said voltage compensation signal is within a second range, wherein a minimum value of said first range is equal to a maximum value of said second range, and said switching control signal is used for controlling a power switch of said power stage circuit.