Abstract: An impedance for short-circuit prevention is connected with a secondary winding side of a transformer of a resonant converter comprising a resonant circuit, a D.C. input source, and a switching devices. The short-circuit prevention impedance is driven by the driving current generated in a driving winding in accordance with a resonance current at the primary winding side of the transformer, thereby obviating the stop of an oscillation. The oscillation can be stopped at a timing of not generating a surge voltage in the switching devices by detecting a current returning to the D.C. input power source.

Abstract: In a self-oscillating type switching power supply in which an input source, a primary winding of a transformer, and a switching element are connected in series, and a constant output is supplied to a load from a secondary winding of the transformer by the operation of the switching element, in order to obtain a signal to turn off the switching element, a sense circuit for detecting the output of the switching power supply is provided, and the analog signal from the sense circuit is inputted to one winding of a saturable reactor, and at a time point when the switching element is to be turned off, the analog input signal is converted into a pulse signal insulated from the analog input signal, and the pulse signal is outputted from another winding of the saturable reactor. By such a system, a switching power supply having a very simple circuit arrangement and high output voltage precision can be achieved.

Abstract: A compact multiple output switching power supply having a series connection of a D.C. input power supply, a switching device and a primary winding of a transformer which supplies currents to loads during an on period of the switching device, and supplies constant output voltages V.sub.i (i=1, 2, . . . , m) from m (m.gtoreq.2) secondary windings n.sub.i (i=1,2, . . . , m) of the transformer by turning on and off the switching device, includes means for storing a magnetic energy during the on period of the switching device and discharging the stored energy to the loads during on off period, connected in series with the primary winding of the transformer. The output voltage V.sub.j (j=2, 3, . . . , m) is represented byV.sub.j =(n.sub.j /n.sub.1).multidot.(V.sub.1 +k.sub.1)-k.sub.jwhere k.sub.j is a voltage drop in the circuit.

Abstract: In accordance with the present invention, there is provided a power supply apparatus comprising a primary winding of a main transformer and a semiconductor device with a control electrode connected in series between both electrodes of a DC power source, a drive current being fed to said control electrode of said semiconductor device via an auxiliary transformer, and output being obtained on a secondary winding of said main transformer by turning on and off of said semiconductor device, wherein a tertiary winding is provided on said main transformer and a negative polarity drive current is flowed into said semiconductor device via said tertiary winding when said semiconductor device is to turn off.