Patent ID: 9136767
Filing Date: 2015-09-15
Classification: H02M

Abstract:
1. A switching power-supply device comprising: a transformer including a primary coil, a secondary coil and an auxiliary coil; a switching element connected in series with the primary coil, an oscillation circuit configured to output a signal to turn on the switching element; an output voltage generation circuit configured to generate an output voltage from a voltage generated in the secondary coil; a control circuit power-supply-voltage generation circuit configured to generate a power-supply voltage for a control circuit from a voltage generated in the auxiliary coil; a feedback control circuit configured to control an ON width of the switching element by using, as a feedback signal, the voltage generated in the auxiliary coil according to an on-and-off operation of the switching element; a voltage reduction detection circuit configured to output a pulse signal as a voltage reduction signal to the secondary coil when a reduction of the output voltage is detected; a voltage-reduction-signal detection circuit configured to detect the voltage reduction signal transmitted to the primary coil from the secondary coil, the voltage-reduction-signal detection circuit comprising a first capacitor AC-coupled to a connection point between the primary coil and the switching element; and a trigger circuit configured to output a trigger signal to turn on the switching element when the voltage reduction signal is detected by the voltage-reduction-signal detection circuit.