PFM CONTROL CIRCUIT, PFM CONTROL SYSTEM AND PFM CONTROL METHOD

摘要

A PFM control circuit includes a switching circuit, a slope-decision circuit, a flip-flop, a first and a second comparison circuits. The first comparison circuit outputs a first signal according to an output voltage of a power conversion circuit. The switching circuit outputs a switching signal according to an output current of the power conversion circuit. The slope-decision circuit outputs a slope modulation voltage, and determines a slope modulation voltage with a first or a second slope according to the switching signal. The second comparison circuit outputs the second signal according to the slope modulation voltage. The flip-flop outputs a control signal to the power conversion circuit according to the first and the second signals. When the slope modulation voltage has the first or the second slope, the control signal has a first or a second frequency accordingly. The first frequency is higher than the second frequency.