POWER SOURCE SELECTING APPARATUS

PROBLEM TO BE SOLVED: To provide a power source selecting apparatus neither causing unstable operations of the circuits connected for supply of power to an output terminal nor generating a through current. SOLUTION: The power source selecting apparatus includes a PMOS transistor 11a and a PMOS transistor 11b connected in series between a voltage source input terminal 1 and a voltage source output terminal 3 and a PMOS transistor 11c and a PMOS transistor 11d connected in series between a voltage source input terminal 2 and the voltage source output terminal 3. On the occasion of switching the power source voltage, the PMOS transistors 11a to 11c are set to shut-off state and the PMOS transistor 11d to conductive state to supply a voltage impressed to the voltage source input terminal 2 to the voltage source output terminal 3 via a parasitic diode of the PMOS transistor 11c. COPYRIGHT: (C)2010,JPO&INPIT