| 摘要 |
PURPOSE:To perform secure switching to a backup power source by providing a switching element which turns off when a power source becomes down between a load and the power source. CONSTITUTION:When the power source A is connected by turning on a switch 2, the comparison voltage of the 1st comparing circuit 4 is boosted by the series circuit of resistances R3 and R4 above a reference voltage and the output of the comparing circuit 4 is inverted to a level '0'. Therefore, a transistor Tr1 turns on and the voltage of the power source A is supplied to the load 1 from an output terminal 7. Then, when the power source A becomes down owing to a power failure, etc., the Tr1 turns off, so the potential VS at the output terminal 7 drops and the base current of a transistor switch Tr2 is controllable when VS=VregX(R5+R6)/R6. Therefore, said VS is supplied continuously to the load 1 from the output terminal 1. |
