Semiconductor switch control circuit and switching power source device

A switching power source device comprising:

• a semiconductor switch having a source electrode, a drain electrode and a gate electrode;
• and
• a semiconductor switch control circuit configured to perform an ON/OFF control of the semiconductor switch with a supply of a drive current to the gate electrode of the semiconductor switch, wherein
• the semiconductor switch control circuit comprises:
• a pulse signal generating part configured to generate a pulse signal which becomes a time reference for performing the ON/OFF control of the semiconductor switch;
• a drive current generating part configured to generate the drive current based on the pulse signal which the pulse signal generating part generates and to supply the drive current to the gate electrode of the semiconductor switch;
• a gate voltage detecting part configured to detect a gate voltage of the semiconductor switch;
• and
• a drive current control part configured to control the drive current which the drive current generating part generates based on the pulse signal which the pulse signal generating part generates and the gate voltage which the gate voltage detecting part detects,
• wherein the drive current control part is configured, when a self-oscillation phenomenon of the gate voltage is detected during a first period after starting a first plateau period of the gate voltage during a turn-off period, to control the drive current so as to set a lowering speed of the gate voltage lower than the lowering speed of the gate voltage before the detection of the self-oscillation phenomenon.