Discharging circuit for power source device with rectifier circuit

Claim 1

A direct-current power supply comprising: a rectifier connectable to an alternating-current power source for providing a direct-current output; a pair of load terminals connected to said rectifier; a smoothing capacitor connected between said load terminals; a switching circuit connected between said load terminals in parallel with said smoothing capacitor; a time constant selection circuit connected across the output of said rectifier; a diode connected between said rectifier and one of said load terminals to permit flow of current from said rectifier to said load terminals and to prevent flow of current from said smoothing capacitor to said time constant selection circuit; and a Schmitt circuit having its input connected to said time constant selection circuit and its output connected to said switching circuit and arranged to minimize said switching circuit in a non-conducting state when the rectified voltage across said time constant selection is substantially equal to the charged voltage of said smoothing capacitor and to turn on said switching circuit only when the voltage across said time constant selection circuit falls below a predetermined value lower than the charge voltage of said smoothing capacitor in response to disconnection of said power source, whereby said switching circuit operates to discharge said smoothing capacitor when said rectifier is disconnected from said power source.