Method of controlling speed of brushless motor of ceiling fan and the circuit thereof

A circuit for controlling a speed of a brushless motor of a ceiling fan, comprising:

• a power rectifying and filtering unit connected to an AC power to transform the AC power to a DC power;
• an AC power feedback unit connected to the power rectifying and filtering unit to monitor the AC power and to output voltage signals of the AC power;
• a central processing unit, which has a control program therein, connected to the AC power feedback unit and to receive the voltage signals;
• a motor driving unit connected to the power rectifying and filtering unit and the central processing unit to be controlled by the central processing unit for driving the brushless motor;
• a motor pulse width modulation (PWM) duty consumption sampling unit connected to the motor driving unit and the central processing unit to sense a current consumption of the motor driving unit and to transform the current consumption into a voltage signal, and the voltage signal is sent to the central processing unit;
• and
• a motor speed sampling unit connected to the motor driving unit and the central processing unit to sense a speed signal of the brushless motor, and the speed signal is sent to the central processing unit;
• wherein the central processing unit receives both of the voltage signal and the speed signal from the motor PWM duty sampling unit and the motor speed sampling unit respectively to have a relation of a PWM duty and the speed of the brushless motor.