Switching regulated power supply apparatus including a resonant circuit

Abstract

A switching regulated power supply apparatus, comprising: an alternative current power source, a first rectifier for rectifying the alternate current output, a high frequency reference pulse generator, a pulse width modulator for modulating the pulse width of the reference pulse output as a function of a control signal, a switching transistor for on/off controlling the output from the first rectifier as a function of the pulse width modulated output, a high frequency transformer connected in series with the first rectifier and the switching transistor, a second rectifier for rectifying the output from the high frequency transformer, and a smoothing circuit for smoothing the output from the second rectifier, the output from the smoothing circuit being applied to the pulse width modulator as a control signal, characterized in that the said apparatus further comprises a resonance capacitor coupled to the said high frequency transformer for causing resonance cooperatively with the said high frequency transformer when the said switching transistor is turned off, and a switching device coupled to the output of the second rectifier to be turned on responsive to a flyback pulse obtained from the smoothing circuit when the switching transistor is turned off, whereby the said resonance is suppressed by means of the second rectifier and the switching device in the latter half cycle of the resonance during the off time period of the switching transistor.