PFM control circuit, PFM control system and PFM control method

A PFM control system, comprising:

• a power conversion circuit, configured to generate an output signal according to a control signal to charge and to discharge to a load;
• and
• a PFM control circuit, comprising:
• a first comparison circuit, configured to output a first signal of an output voltage according to the output signal;
• a switching circuit, configured to output a switching signal according to an output current of the output signal;
• a slope decision circuit, configured to output a slope modulation voltage, and to decide the slope modulation voltage with a first slope or a second slope according to the switching signal;
• a second comparison circuit, configured to output a second signal according to the slope modulation voltage;
• and
• a flip-flop circuit, configured to output the control signal to the power conversion circuit according to the first signal and the second signal.

A PFM control method, comprising:

• outputting, by a PFM control circuit, a control signal;
• charging and discharging, by a power conversion circuit, to a load according to the control signal, so as to generate an output signal;
• determining whether the load connected to the power conversion circuit is at a light loading according to the output signal, and determining whether a frequency of the control signal is lower than a frequency of a low frequency signal;
• switching a capacitance array of the PFM control circuit into a first capacitance value when the load is at the light loading and the frequency of the control signal is lower than the frequency of the low frequency signal, so as to generate the control signal with a first frequency;
• and
• switching the capacitance array of the PFM control circuit into a second capacitance value when the load is not at the light loading or the frequency of the control signal is not lower than the frequency of the low frequency signal, so as to generate the control signal with a second frequency, wherein the first capacitance value is smaller than the second capacitance value, the first frequency is higher than the second frequency.