System and method for controlling forward/reverse rotation of fan

A control method for a control system, the control system controlling a fan of an electronic device according to a pulse width modulation signal outputted from the electronic device, the control system comprising a motor for rotating the fan, the control method comprising steps of:

• (a) starting the control system;
• (b) controlling the motor to be operated in a forward rotation mode;
• (c) double-checking whether a duty cycle of the pulse width modulation signal is lower than or equal to a first threshold value;
• (d) if the duty cycle of the pulse width modulation signal is lower than or equal to the first threshold value in the step (c), switching operation mode of the motor from the forward rotation mode to a reverse rotation mode;
• (e) double-checking whether the duty cycle of the pulse width modulation signal is higher than or equal to a second threshold value;
• (f) if the duty cycle of the pulse width modulation signal is not higher than or equal to the second threshold value in the step (e), judging whether the motor has been operated in the reverse rotation mode for a predetermined reverse time period;
• and
• (g) if the motor has been operated in the reverse rotation mode for a predetermined reverse time period in the step (f), performing the step (b) again.

A control system for controlling forward/reverse rotation of a fan of an electronic device, the control system comprising:

• a motor for driving rotation of the fan;
• an interface circuit for receiving and converting a pulse width modulation signal;
• a motor controller electrically connected with the motor for controlling a rotation speed of the motor and controlling the motor to be operated in a forward rotation mode or a reverse rotation mode, wherein the fan is forwardly rotated to dissipate heat when the motor is operated in the forward rotation mode, and the fan is reversely rotated to eliminate dust when the motor is operated in the reverse rotation mode;
• a detection control circuit electrically connected with the interface circuit and the motor controller for reading a duty cycle of the converted pulse width modulation signal in real time, wherein when the motor is operated in the forward rotation mode, the detection control circuit drives the motor controller to control the rotation speed of the fan according to the duty cycle, and the detection control circuit double-checks whether the duty cycle is lower than or equal to a first threshold value, wherein if the duty cycle is lower than or equal to the first threshold value, the detection control circuit drives the motor controller to switch operation mode of the motor from the forward rotation mode to the reverse rotation mode;
• a frequency simulation circuit electrically connected with the detection control circuit, wherein while the motor is in an inertia stop state, the frequency simulation circuit issues a simulated frequency signal to the electronic device;
• and
• a frequency output circuit electrically connected with the motor controller and the detection control circuit, wherein while the motor is operated in the forward rotation mode or the reverse rotation mode, an actual frequency signal corresponding to the rotation speed of the motor is outputted from the frequency output circuit to the electronic device through the detection control circuit and the frequency simulation circuit.