Abstract: A power supply comprises an inverter circuit for converting an input voltage from a d.c. voltage source to a desired output voltage which is maintained constant under varying current of a load circuit through the feedback operation of an inverter controller. A threshold circuit including a breakdown diode is connected to the d.c. voltage source. The base of a voltage sensing transistor is connected to the breakdown diode for switching to a conducting state when the d.c. voltage exceeds a prescribed level determined by threshold voltages of the breakdown diode and the voltage sensing transistor. A pair of current carrying transistors are connected between the d.c. voltage source and a power supply terminal of the inverter controller. Responsive to the condition of the voltage sensing transistor current is supplied through the current carrying transistors from the d.c. voltage source to the inverter controller. The source voltage supplied to the inverter controller is held at zero volt until the d.c.

Abstract: A system-power-supply-source controller is used for controlling and monitoring the operations of a plurality of power supply sources associated with a plurality of logical units. The logical units each comprise power supply control units. Separate and independent power supplies are provided for each power supply control unit and its respective logical unit. The system-power-supply-source controller transmits and receives data to and from control units associated with each logical unit. A data signal line is provided for transferring data between the system-power-supply-source controller and the control units. An interruption line is arranged between the controller and the logical units, and each control unit produces a signal on the interruption line to inform the system-power-supply-source controller that its associated power supply source has malfunctioned.