Patent attributes
A switching power-supply unit uses a time when a transformer voltage Vt inverts due to a rectifier diode (Ds1) entering a non-conducting state as a trigger, and a first switching control circuit (CNT1) turns on a first switching element (Q1) after a predetermined delay time passes. A second switching control circuit (CNT2) turns on a second switching element (Q2) using a time when the transformer voltage Vt inverts due to turning off of the first switching element (Q1) as a trigger. A third switching control circuit (CNT3) turns on a third switching element (Q3) using turning off of the second switching element (Q2) as a trigger. The first switching control circuit (CNT1) determines a period ton1 of the first switching element (Q1) such that a first output voltage Vo1 is set to a predetermined value. The second switching control circuit (CNT2) determines an ON-period ton2 of the second switching element (Q2) such that a second output voltage Vo2 is set to a predetermined value. The third switching control circuit (CNT3) determines an ON-period ton3 of the third switching element (Q3) such that a third output voltage Vo3 is set to a predetermined value.
