PURPOSE: To cope with fluctuation of load voltage without interrupting power supply to the load by providing an LED connected with the output terminal of a voltage supply, a diode connected between the output terminal and a joint, and a resistor connected between a voltage detecting terminal and the joint.

CONSTITUTION: When the voltage of a power supply 1 is set lower than the voltage of a power-supply 2, power is fed from the power supply 1 through a diode d11 to a load 3. Since the voltage V3 across the load 3 is higher than the set voltage of the power supply 2, the power supply 2 functions to lower the output voltage and thereby the voltage V2 of the power supply 2 drops below a voltage V3 thus turning a diode d21 OFF. The power-supply 2 functions to lower the output voltage furthermore, but a diode d22 connected between the remote sensing terminal +s and the power supply terminal (o) of the power supply 2 is turned ON to clamp the voltage V2 of the power supply 2 and thereby the system enters into waiting state before the voltage V2 drops to 0V.