Patent ID: 8031490

Claim:
A power supply circuit configured to self-oscillate by supply of power from a power supply section, the power supply circuit being comprising: a resonance section including a resonance capacitor and a resonance coil, and adapted for supplying power to a load device; an oscillation section including a first switching element connected in series to said resonance section and a feedback coil magnetically coupled to said resonance coil, and adapted for turning on and off said first switching element to cause said resonance section to self-oscillate; a turn-off section including a second switching element and a turn-off capacitor connected between a control terminal of said second switching element and a negative electrode of the power supply section, wherein when an on-current which flows when said first switching element turns on reaches a predetermined level, said second switching element turns on to cause said first switching element to turn off; and a first charging section including a diode of which an anode is connected to said feedback coil side, and a zener diode of which a cathode is connected to a cathode of said diode and of which an anode is connected to said turn-off capacitor side, wherein said zener diode is operated when a voltage larger than a fixed value is outputted from the power supply section to charge said turn-off capacitor, wherein said first charging section is connected in parallel and in multiple numbers, and wherein each zener diode provided in each first charging section has a different breakdown voltage respectively.