Electronic switching power supply

Claim 1

An electrical switching power supply for supplying power to an electrical load from a variable voltage level AC or DC voltage source having first and second terminals, comprising: a transformer (5) having a primary coil with first and second terminals and a secondary coil with first and second terminals, said first terminal of said secondary coil being connected to said electrical load; a first transistor (1) having a base, an emitter and a collector, the emitter-collector-path of said first transistor being coupled in series with said primary coil, the series connection of said emitter-collector-path of said first transistor and said primary coil being electrically coupled to said variable level AC or DC voltage source; a first diode (31) having a cathode and an anode connected in series with said secondary coil and said electrical load; a first capacitor (11) connected between said base of said first transistor and said second terminal of said secondary coil; a second transistor (2) having a base, an emitter and a collector, said collector of said second transistor being connected to said base of said first transistor and said emitter of said second transistor being connected to said second terminal of said voltage source; a first resistor (21) connected between said first terminal of said voltage source and said base of said first transistor; a second resistor (22) connected between said first terminal of said secondary coil and said emitter of said first transistor; a third resistor (23); a first Zener diode (41) having an anode and a cathode connected between said emitter of said first transistor and said base of said second transistor; a third transistor (3) having a base, an emitter and a collector, said emitter of said third transistor being connected to said first terminal of said secondary coil; a second diode (32) having a cathode and an anode; a third diode (33) having a cathode and an anode, said cathode of said second diode being connected to said second terminal of said secondary coil and said anode of said second diode being connected to both the anode of said third diode and to the base of said third transistor through said third resistor; a fourth resistor (24) connected between said collector of said third transistor and said base of said second transistor; a fifth resistor (25) connected between said first terminal of said secondary coil and said collector of said second transistor; and a discharge circuit connected between said first capacitor and said electrical load; whereby said first capacitor is electrically charged during a conducting phase of said first transistor, and during a subsequent blocking phase of said first transistor, said electrical load receives the charge build up in said first capacitor during the said conducting phase.