1. Field of the Invention
The present invention relates to a controller of a DC brushless motor. More specifically, the present invention relates to the controller for protection against abnormal rotation of the DC brushless motor having a variable rotating speed, which is used, for example, in an electric fan.
2. Description of the Prior Art
Such protection and control apparatus is disclosed for example in the Japanese Patent Application Laying-open No. 62035/1981 laid-open on May 27, 1981. In the prior art, it is suggested to detect the number of rotation of DC motor to operate a protection circuit for cutting off the power supply to the DC motor when the rotations decreased below a predetermined number. In order to detect the rotation number in the conventional practice, particular rotation number detecting means is necessary, resulting in a complicated controlling apparatus.