Method of starting a fan using an open loop starting stage with a decreasing drive signal value

1. A fan, comprising:

an impeller;

a control circuit comprising a control unit; and

a motor, connected to the impeller and electrically connected to the control circuit, the motor configured to continuously receive a first driving signal from the control unit to drive the impeller during a full period of a first time period of a fan open loop start-up stage, and configured to continuously receive a second driving signal from the control unit to drive the fan during a second time period of the fan open loop start-up stage, wherein the fan at a stop status directly enters the first time period of the fan open loop start-up stage when starting to drive the fan;

wherein a signal value of the first driving signal is initially greater than a signal value of the second driving signal, and decreases from a beginning of the first driving signal until being equal to the signal value of the second driving signal;

wherein an initial signal value of the first driving signal is at a minimum duty cycle for starting the fan, an initial signal value of the second driving signal is at a minimum duty cycle for operating the fan, and the minimum duty cycle for starting the fan is larger than the minimum duty cycle for operating the fan;

wherein the signal value of the first driving signal linearly decreases, the signal value of the second driving signal is an unchanged value;

wherein the first time period and the second time period are adjusted for a different fan but the sum of the first time period and the second time period is always the same.

2. The fan of claim 1 , wherein the signal value of the second driving signal is a constant value.

3. The fan of claim 1 , wherein the control circuit further comprises:

a detection unit, detecting the current phase or back emf of the motor and outputting a feedback signal to the control unit,

wherein after completing the fan open loop start-up stage, the control unit provides a third driving signal to drive the fan according to the feedback signal.

4. The fan of claim 3 , wherein the third driving signal is PWM signal or DC voltage signal.

5. The fan of claim 1 , wherein the first driving signal and the second driving signal are PWM signals or DC voltage signals.

6. The fan of claim 1 , wherein,

at a beginning of the first time period, the first driving signal increases a rotational speed of the fan.

7. The fan of claim 6 , wherein,

during the full period of the first time period, the first driving signal increases the rotational speed of the fan; and

during a full period of the second time period, the second driving signal increases the rotational speed of the fan.

8. A method for controlling a fan in a fan open loop start-up stage including a first time period and a second time period, comprising:

during a full period of the first time period of the fan open loop start-up stage, a motor of the fan continuously receiving a first driving signal to drive the fan, wherein the fan at a stop status directly enters the first time period of the fan open loop start-up stage when starting to drive the fan;

during the second time period of the fan open loop start-up stage, the motor of the fan continuously receiving a second driving signal to drive the fan,

wherein a signal value of the first driving signal is initially greater than a signal value of the second driving signal, and decreases from a beginning of the first driving signal until being equal to the signal value of the second driving signal;

wherein an initial signal value of the first driving signal is at a minimum duty cycle for starting the fan, an initial signal value of the second driving signal is at a minimum duty cycle for operating the fan, and the minimum duty cycle for starting the fan is larger than the minimum duty cycle for operating the fan;

wherein the signal value of the first driving signal linearly decreases, the signal value of the second driving signal is an unchanged value;

wherein the first time period and the second time period are adjusted for a different fan but the sum of the first time period and the second time period is always the same.

9. The method of claim 8 , wherein the signal value of the second driving signal is a constant value.

10. The method of claim 8 , wherein the fan comprises an impeller and a control circuit, the motor is connected to the impeller and drives the impeller to operate, the motor is electrically connected to the control circuit, the control circuit comprises a control unit and a detection unit, the detection unit detects the current phase or back emf of the motor to output a feedback signal to the control unit, the method further comprises:

after completing the fan open loop start-up stage, providing a third driving signal to drive the fan according to the feedback signal.

11. The method of claim 10 , wherein the first driving signal, the second driving signal and the third driving signal are provided by the control unit.

12. The method of claim 10 , wherein the third driving signal is PWM signal or DC voltage signal.

13. The method of claim 8 , wherein the first driving signal and the second driving signal are PWM signals or DC voltage signals.

14. The method of claim 8 , wherein

at a beginning of the first time period, the first driving signal increases a rotational speed of the fan.

15. The method of claim 14 , wherein

during the full period of the first time period, the first driving signal increases the rotational speed of the fan; and

during a full period of the second time period, the second driving signal increases the rotational speed of the fan.