To prevent charging to a primary battery by the current from an AC adapter and to normally perform power supply switching even when an increase in contact failure or contact resistance are caused by generating oxide coating on a contact with a connecting terminal of the AC adapter.
A positive electrode of the primary battery 17 is connected to a source of a FET1. A drain of the FET1 is connected to the drain of a FET2. The source of the FET2 is connected to the positive electrode of a load 19 side. The positive electrode of a connecting terminal 15 is so connected to the positive electrode of the load 19 side as the current flows from the positive electrode of the connecting terminal 15 to the positive electrode of the load 19 side through a reverse-current preventing circuit 18. By mutually connecting the positive electrode of the connecting terminal 15 to the gate of the FET1 and the FET2, for only the primary cell 17, the switching circuit is so switched that the electric power is supplied from the primary battery 17 to the load 19, and when the AC adapter is connected to the connecting terminal 15, the switching circuit is so switched that the electric power is supplied from the AC adapter to the load 19.
NIKAIDO SHINICHI
TAKASHIMA TORU
TOKURA TAKESHI
Iwa Saki Kokuni
Kawamata Sumio
Shunichi Takahashi
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