Switching power circuit and control method for switching power circuit

A control method for a switching power circuit comprising a first rectification circuit for rectifying an alternating current power so as to generate a first pulsating voltage, a switching circuit for controlling ON/OFF of said first pulsating voltage based on a control signal which is input so as to generate a first alternating current voltage having a predetermined frequency higher than a frequency of said alternating current power and having a pulse width corresponding to said control signal, a transforming circuit for transforming said first alternating current voltage so as to generate a second alternating current voltage of a predetermined voltage value, a second rectification circuit for rectifying said second alternating current voltage so as to generate a second pulsating voltage and a smoothing circuit for smoothing said second pulsating voltage so as to generate a direct current voltage and for applying said DC voltage to a load, said control method comprising:

• a voltage change detecting process of detecting a change of said direct current voltage in a period longer than a period of a ripple included in said direct current voltage so as to generate a detection signal;
• and
• a control signal generating process of generating said control signal used to execute a negative feed-back control for said pulse width of said first alternating current voltage based on a level of said detection signal.