Control circuit and method for efficient flyback power converter under light load

摘要

A flyback power converter includes a power switch connected to a primary side of a transformer, and a sensing signal is provided for a control circuit to switch the power switch so as for the transformer to convert an input voltage into an output voltage. The sensing signal is a function of the input voltage, and the control circuit extracts a variation of the sensing signal during a preset time period. The variation of the sensing signal is used to prevent the output ripple and the green mode entry point of the flyback power converter from varying with the input voltage.