To provide an overdischarge prevention circuit for a primary battery, and a multisystem power supply circuit fitted with this circuit, which shuts out even a feeble discharge of a battery when the battery becomes in a discharge stop state, and surely evades the discharge of the battery.
A main switching element Q1 is arranged in a power supply route 2 connecting a primary battery B and a load Z, and this element Q1 is on/off-controlled by a controlling switching element Q2. A divided voltage output by resistors R3, R4 connected to the supply route 2 on the load Z side rather than the element Q1, is inputted to the base of the element Q2. If the battery voltage becomes lower than a set voltage, the element Q2 is turned off. Consequently, the base current of the element Q1 is interrupted and the element Q1 is turned off too. Any feeble current does not flow from the battery B, and discharge of the battery is completely stopped. By closing a switch SW1 after a battery exchange and inputting the battery voltage directly to the element Q2, the element Q2 is turned on, and the element Q1 is turned on.
YAMADA KATSUO
AKATANI TOMOYUKI
