Charge and discharge control circuit

DETAILED DESCRIPTION To solve the above problems, the charge and discharge control circuit of the present invention controls a charge and discharge of a secondary cell connected to an external power source terminal through a switch circuit by ON/OFF controlling the switch circuit.
The charge and discharge control circuit further comprises an overcharge detecting circuit for detecting whether the secondary cell is in the overcharge state, a delay circuit for outputting a delayed output from the overcharge detecting circuit by a predetermined delay time, and a high voltage supplying state by detecting circuit for detecting whether a voltage of a predetermined level higher than the overcharge detecting voltage detected by said overcharge detecting circuit is being supplied to the high voltage supplying state supplied by said secondary cell, wherein the switch circuit is turned OFF so as to stop charging of the cell when at least either the overcharge state or the high voltage supplying state is detected responding to the delay circuit and the high voltage detecting circuit.
According to the above-described construction, when a voltage at a predetermined level higher than the overcharge detecting voltage is rapidly supplied for some reason, the high voltage detecting circuit detects it and turns off the switch circuit instantly, and the high voltage detecting circuit thus prevents high voltage from being supplied to the secondary cell without waiting for the output of the overcharge detecting circuit to be obtained through the delay circuit.
Even when the terminal voltage of the secondary cell rises and exceeds the high level of the above-described predetermined level, the high voltage detecting circuit operates to stop the switch circuit to prevent further charging of the cell, and prevents high voltage from being supplied to the secondary cell.