Seiko Instruments Inc

Tsutomu Ando

Yoshihisa Tange

The invention provides a power source circuit which is capable of preventing a current from being caused to flow from a battery charger to a secondary battery in the over-charge detection state. In order to cut off a current from a parasitic diode of a transistor having a gate electrode to which a signal to release the over-current state is inputted from a switching-device-controlling logic circuit, a charge and discharge controlling circuit includes a diode connected between the transistor and a current detecting circuit, thereby preventing a current from being caused to flow from the battery charger to the secondary battery.

Power source circuit

A charge control circuit which prevents charging of a battery when a charger is connected to the battery when the voltage of the battery is not above a threshold voltage of a MOS inverter circuit. Under such a condition, a charge control switch is turned off and charging current is cut off so that charging of the abnormal battery is inhibited and destruction or explosion of the battery is prevented. First and second circuits monitor the battery voltage, the second circuit having for comparing the battery voltage to a threshold voltage of a MOS transistor, and a logic circuit performs a logic operation on the outputs of the two circuits so that charging of the battery is prevented when the battery voltage is not higher than the threshold voltage of the MOS transistor.

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Chiba, Japan

Tsutomu Ando