Voltage-step-down circuit with chopping transistor for D-C power supply

Claim 1

A step-down circuit for deriving a reduced output voltage from the voltage of a d-c supply connected across a pair of conductors, comprising: a chopping transistor connected in series with one of said conductors between an input end and an output end thereof, said transistor being provided with a control electrode; voltage-smoothing filter means including a shunt capacitance connected across said conductors downstream of said transistor; a control loop including in series an electronic switch, a first resistor and an ancillary source of d-c voltage substantially lower than the supply voltage, said first resistor being part of a voltage divider also including a second resistor, said first resistor being inserted between said control electrode and the other of said conductors while being galvanically separated from said control electrode by said second resistor and by a coupling capacitor interposed between said voltage divider and said control electrode, said second resistor lying outside said loop; and pulse-generating means connected to said electronic switch for alternately opening and closing same in a predetermined rhythm whereby said series resistor is traversed by a pulsating current rendering said resistor intermittently conductive.