Patent ID: 8378611

Claim:
An alarm circuit to alarm abnormal state of a computer fan, the computer fan connected to a motherboard socket, the motherboard socket comprising a power terminal, a control terminal, and a detecting terminal, the computer fan comprising a power pin, a control pin, and a detecting pin, the power terminal connecting to the power pin to provide a power source to the computer fan, the control terminal connecting to the control pin to provide a speed control signal to drive the computer fan, the detecting terminal connecting to the detecting pin to receive a speed signal fed back from the computer fan, the alarm circuit comprising: a detection circuit that detects the power source provided to the computer fan; a controller coupled to the detection circuit to receive the power source detected by the detection circuit and coupled to the motherboard socket to receive the speed control signal, the controller also coupled to the computer fan to receive the speed signal; an alarm unit coupled to the controller; and a relay coupled to between the power terminal and the power pin; wherein the controller generates a normal speed range according to the power source data and the speed control signal, and compares the normal speed range with the speed signal to determine if the computer fan works in an abnormal state, the controller further comprises a first output terminal coupled to the relay to transmit a cut off signal to the relay when the computer fan works in an abnormal state, the relay cuts off the power source provided to the computer fan to protect the computer fan when receives the cut off signal, the alarm unit sounds an alarm when the computer fan works in an abnormal state.