Patent ID: 8625314

Claim:
A switching power supply apparatus comprising: a power supply voltage receiving unit is arranged to receive an input power supply voltage; a direct current voltage outputting unit is arranged to output a direct current voltage; a transformer including a primary winding and a secondary winding; a low-side switching element connected in series to the primary winding to apply a voltage of the power supply voltage receiving unit to the primary winding in response to turning on of the low-side switching element; a high-side switching element having a ground level that is different from that of the low-side switching element; and a switching control circuit including a low-side switching control unit that is programmed to control the low-side switching element and a high-side switching control unit that is programmed to control the high-side switching element; wherein the low-side switching control unit includes a winding voltage polarity reversal detection circuit, a low-side turn-off circuit, and a low-side turn-off delay circuit, the winding voltage polarity reversal detection circuit is arranged to detect reversal of a polarity of a winding voltage of the transformer, the low-side turn-off circuit is arranged to turn off the low-side switching element when the reversal of the polarity of the winding voltage of the transformer is detected by the winding voltage polarity reversal detection circuit during a period in which a drive voltage signal is supplied to the low-side switching element, the low-side turn-off delay circuit is arranged to determine a delay time from a time when the polarity of the winding voltage of the transformer is reversed to a time when the low-side switching element is turned off; the high-side switching control unit includes a high-side turn-on delay circuit that delays a time from the time when the polarity of the winding voltage of the transformer is reversed to a time when the high-side switching element is turned on; and the delay time of the low-side turn-off delay circuit is shorter than the delay time of the high-side turn-on delay circuit.