Self-oscillation type switching power supply apparatus

摘要

A self-oscillation type switching power supply apparatus comprises: a transformer (T) having a primary winding (N1), a secondary winding (N2), and a feedback winding (NB); a switching transistor (Q1) for interrupting a current in said primary winding (N1); a controlling transistor (Q2) for controlling a positive feedback signal for said switching transistor (Q1)from said feedback winding (NB); a time constant circuit (C3, R4) adapted to be charged by a voltage produced in said feedback winding (NB) at a predetermined time constant and to give a controlling voltage to said controlling transistor (Q2); a light emitting element (PD) of a photocoupler provided in a circuit for detecting an output voltage or output current from the secondary winding (N2) of said transformer (T); a photodetector (PT) of said photocoupler connected to said time constant circuit (C3, R4) whereby the time constant of said time constant circuit is changed in dependence on the detection of the output voltage or output current to stabilize the output voltage or output current; and a conducting path (R1, R11, D4) provided between an input power-supply voltage supplying section for the primary winding (N1) of said transformer (T) and a voltage-supplying section for said photodetector (PT) of the photocoupler. <IMAGE>