Patent ID: 7755311

Claim:
A fan abnormality detection device, comprising: a fan for cooling an electronic device; a fan drive circuit which controls a fan drive current so that the temperature of said electronic device does not attain a high temperature, and which, when said fan drive current has become excessive for a fixed time period T 1 , cuts off said fan drive current, waits for a time period T 2 , and thereafter allows said fan drive current to flow again; a fan power supply current detection sensor which detects a fan power supply current supplied to said fan drive circuit; a first decision means which determines that said fan is in a locked state or a short circuited state, when it is detected by said fan power supply current detection sensor that a fan power supply current of a first current value I 1 which flows in the fan locked state has continued over a time period T 3 which is less than or equal to said fixed time period TI; and a second decision means which determines an open circuit state, when it is detected by said fan power supply current detection sensor that a fan power supply current of a second current value I 2 which flows to said fan in a state in which its current input circuit is in the disconnected state has continued over a time period T 4 which is greater than or equal to said fixed time period TI.