| 摘要 |
PURPOSE:To lengthen service life of a sub-battery power supply for applying a voltage on one input terminal by feeding the positive power supply of an inverter from an output terminal, providing transistors, respectively, between source and drain of a switching transistor and a substrate, and driving the switching transistor and respective transistors at the input or output terminal of the inverter. CONSTITUTION:When main power supply at an input terminal 1 is removed and only a sub-power supply is applied on an input terminal 2, input terminal of an inverter 4 goes LOW and a voltage is applied from the sub-power supply onto an output terminal 6 thus supplying a voltage to the inverter 4. Consequently, output of the inverter 4 is inverted to High level. As a result, a transistor 8 is turned OFF and a transistor 9 is turned OFF and thereby a switching transistor 5 is turned OFF to short-circuit the electrode on the output 6 side of the switching transistor 5 and a substrate thus forming a parasitic diode having an anode and a cathode, respectively, on the input terminal 1 side and the output terminal 6 side. Since the diode has a positive potential at the output terminal 6 and a ground potential at the input terminal 1, it is biased reversely and no current flows from the input terminal 2 toward the input terminal 1. |
