Abstract: There is disclosed a low voltage protection circuit for preventing overdischarging in a back-up battery. The circuit includes: switching a device which supplies voltage to the load and being connected in series between the battery and load; a charging device which charges the battery by being connected in parallel to the switching device; a first control device which determines the different operation-starting and operation-terminating voltage of the battery and, at the same time, controls the "on" and "off" of the switching device by being connected in parallel to the input terminal of the battery; and a second control device which generates hysteresis voltage between the operation-starting and operation-terminating voltage by supplying the voltage which determines the operation-terminating voltage to the first control device.