| 摘要 |
PROBLEM TO BE SOLVED: To suppress increase in a switching frequency, and reduce a loss by providing a period control means for continuing the off-period of a switching element for supplying an electrical energy to a load, even after completing the discharge of excitation energy from secondary coil winding in a control circuit. SOLUTION: A transistor Q3 of a switching circuit 6 for constituting a switching power supply device 1a connects an emitter to the one end of feedback coil winding Nb of a transformer T via a capacitor C3 and a resistor R13 and connects a collector to the gate of an FETQ1 as a main switching element. A base is connected to the other end of the feedback coil winding Nb via a resistor R8. A capacitor C5 and a resistor R9 are respectively connected between the base and emitter of the transistor Q3 in parallel, and a diode D3 is connected between the emitter and corrector of the transistor Q3. The collector of a transistor Q5 is connected to one end of a primary coil winding N1 of the transformer T via a resistor 11, and the emitter, for example, is connected to an excitation resistor R1 to make a constant-current circuit 7, and a starting current of the switching circuit 6 is controlled. |
