Resonant type constant voltage supply apparatus

Claim 1

A constant voltage supply apparatus comprising: at least an input terminal for feeding an input direct current from an external direct current source; at least a switching element connected in series with same input terminal for switching said input direct current; a converter-transformer, a primary winding of said converter-transformer being connected in series with said switching element; a resonance capacitor connected in series with said primary winding of said converter-transformer; a common input terminal connected in series with said resonance capacitor; a first rectifier circuit coupled to a secondary winding of said converter-transformer for producing a rectified signal from a signal appearing across terminals of said secondary winding of said converter-transformer; a smooth circuit for smoothing said rectified signal so as to thereby obtain a dc output voltage; a dc output terminal for feeding said dc output voltage to an external load; a control transformer, a primary winding thereof being connected in parallel with said resonance capacitor, said control transformer further having a third winding for controlling an inductance of said control transformer by means of an electric signal fed thereto as a function of said dc output voltage; and a second rectifier circuit coupled to a secondary winding of said control transformer for rectifying a voltage signal produced across said secondary winding of said control transformer and for directly feeding a rectified voltage to said dc output terminal of said apparatus.