Patent ID: 8289055

Claim:
A host computer comprising: an enclosure; and a motherboard mounted in the enclosure, the motherboard comprising: a battery; a reference voltage generating circuit to generate a reference voltage; an electronic switch; an alarm unit mounted on the enclosure; and a comparator connected to the reference voltage generating circuit and the battery to receive the reference voltage and detect a voltage of the battery, wherein the comparator compares the detected voltage of the battery with the reference voltage, the comparator outputs a control signal to turn on the electronic switch to start the alarm unit upon a condition that the voltage of the battery is less than the reference voltage, wherein the reference voltage generating circuit comprises a Zener diode, and first to third resistors, a cathode of the diode is connected a power terminal of the motherboard by the first resistor, an anode of the diode is grounded, the second resistor and the third resistor are connected in series between the anode and the cathode of the diode, a reference terminal of the diode is connected to a node between the second and third resistors, a non-inverting terminal of the comparator is connected to the cathode of the diode, an inverting terminal of the comparator is connected to a positive terminal of the battery.