POWER SUPPLY SWITCHING-OVER CIRCUIT

PURPOSE:To provide a power supply switching-over circuit whereby a useless power consumption can be reduced. CONSTITUTION:An external power supply 1 and a load circuit 2 are connected by a MOS type FET Q1, and a battery 3 and the load circuit 2 are connected by a MOS type FET Q2. Further, by a differential switching circuit 41 using a FET Q5 and transistors Q6-Q9, the voltage difference between the external power supply 1 and the battery 3 is sensed. Hereupon, according to the sensed result, either the FET Q1 or the FET Q2, which is on the side of the higher voltage one of the voltage sources comprising the external power supply 1 and the battery 3, is brought into ON-state. Therefore, a current is applied to the load circuit 2 from either the external power supply 1 or the battery 3 via either the FET Q1 or the FET Q2 respectively. Thereby, a useless power consumption can be reduced, and the time in which the battery 3 can drive a portable apparatus, etc., can be increased.