Brushless direct current fan

摘要

A brushless direct current fan includes a driving circuit having a Hall device having at least one output terminal connected to the base of a first transistor with the collector of the first transistor connected to a first winding of the fan and also connected to the base of a second transistor via a resistor. The collector of the second transistor is connected to a second winding of the fan. A square wave generation circuit is provided to be coupled to the collector of one of the first and second transistors. The square wave generation circuit is comprised of a current limit resistor and a third transistor wherein the base of the third transistor is connected to the collector of the one of the first and second transistors of the fan via the current limit resistor to obtain an electric signal therefrom which is converted to a square wave signal by the square wave generation and output at the collector of the third transistor. Such a square wave signal may be used to monitor the operation of the fan or may be fed back into the fan driving circuit to control the speed of the fan.