Abstract: An axial fan includes a fan frame, an impeller and a motor. The fan frame has a frame body, a base and plural connecting members. The base is disposed at the center of a side of the frame body. The connecting members connect the frame body to the base. The impeller is accommodated in the frame body and disposed on the base. The impeller has a rotating shaft, a hub and plural blades disposed around the hub. The motor is disposed on the base and connects with the rotating shaft to drive the impeller to rotate. When the impeller rotates forwardly, the airflow is induced to flow through the connecting members, blades, and one side of the frame body away from the base. When the impeller rotates reversely, the airflow is induced to flow through the side of the frame body, blades and connecting members.

Abstract: The invention provides a monitor circuit, which is used for a fan and receives a driving current and a driving voltage of the fan. The monitor circuit includes sensing circuits and a microcontroller. The sensing circuits respectively sense statuses of the fan and output sensing values. The microcontroller is used for monitoring whether the sensing values exceed preset value ranges respectively to obtain comparison results. The microcontroller outputs warning signals according to the comparison results. Each of the warning signals has a specific frequency.

Abstract: An axial fan includes a fan frame, an impeller and a motor. The fan frame has a frame body, a base and plural connecting members. The base is disposed at the center of a side of the frame body. The connecting members connect the frame body to the base. The impeller is accommodated in the frame body and disposed on the base. The impeller has a rotating shaft, a hub and plural blades disposed around the hub. The motor is disposed on the base and connects with the rotating shaft to drive the impeller to rotate. When the impeller rotates forwardly, the airflow is induced to flow through the connecting members, blades, and one side of the frame body away from the base. When the impeller rotates reversely, the airflow is induced to flow through the side of the frame body, blades and connecting members.

Abstract: An axial fan includes a fan frame, an impeller and a motor. The fan frame has a frame body, a base and plural connecting members. The base is disposed at the center of a side of the frame body. The connecting members connect the frame body to the base. The impeller is accommodated in the frame body and disposed on the base. The impeller has a rotating shaft, a hub and plural blades disposed around the hub. The motor is disposed on the base and connects with the rotating shaft to drive the impeller to rotate. When the impeller rotates forwardly, the airflow is induced to flow through the connecting members, blades, and one side of the frame body away from the base. When the impeller rotates reversely, the airflow is induced to flow through the side of the frame body, blades and connecting members.

Abstract: An anti-air-return fan system includes a motor, a driving control circuit, and a rotation judgment circuit. The driving control circuit is electrically connected to the motor. The driving control circuit has a driving signal for driving the motor to rotate according to the driving signal. The rotation judgment circuit outputs a judgment signal to the driving control circuit when detecting that the motor reversely rotate. The driving control circuit executes a braking according to the judgment signal. The driving control circuit drives the motor to operate when the rotation judgment circuit detects that the motor doesn't rotate reversely.

Abstract: The invention provides a monitor circuit, which is used for a fan and receives a driving current and a driving voltage of the fan. The monitor circuit includes sensing circuits and a microcontroller. The sensing circuits respectively sense statuses of the fan and output sensing values. The microcontroller is used for monitoring whether the sensing values exceed preset value ranges respectively to obtain comparison results. The microcontroller outputs warning signals according to the comparison results. Each of the warning signals has a specific frequency.

Abstract: A control method of a fan rotation speed, which controls the operation of a fan set including fans connected in series, is disclosed. The control method includes the steps of acquiring a control factor; judging whether the control factor is less than a first threshold value; executing a first control procedure when the control factor is less than the first threshold value; judging whether the control factor is greater than a second threshold value when the control factor is greater than the first threshold; executing a second control procedure when the control factor is greater than the second threshold value; and executing a third control procedure when the control factor is less than the second threshold value.

Abstract: A fan control method includes the steps of: acquiring a control factor; determining whether the control factor is located in a first range or a second range; executing a first dust removing mode if the control factor is located in the first range; executing a second dust removing mode if the control factor is located in the second range; and executing a normal mode if the control factor is not located in the first range and the second range.

Abstract: An anti-air-return fan system includes a motor, a driving control circuit, and a rotation judgment circuit. The driving control circuit is electrically connected to the motor. The driving control circuit has a driving signal for driving the motor to rotate according to the driving signal. The rotation judgment circuit outputs a judgment signal to the driving control circuit when detecting that the motor reversely rotate. The driving control circuit executes a braking according to the judgment signal. The driving control circuit drives the motor to operate when the rotation judgment circuit detects that the motor doesn't rotate reversely.

Abstract: An axial fan includes a fan frame, an impeller and a motor. The fan frame has a frame body, a base and plural connecting members. The base is disposed at the center of a side of the frame body. The connecting members connect the frame body to the base. The impeller is accommodated in the frame body and disposed on the base. The impeller has a rotating shaft, a hub and plural blades disposed around the hub. The motor is disposed on the base and connects with the rotating shaft to drive the impeller to rotate. When the impeller rotates forwardly, the airflow is induced to flow through the connecting members, blades, and one side of the frame body away from the base. When the impeller rotates reversely, the airflow is induced to flow through the side of the frame body, blades and connecting members.

Abstract: A fan control method includes the steps of: acquiring a control factor; determining whether the control factor is located in a first range or a second range; executing a first dust removing mode if the control factor is located in the first range; executing a second dust removing mode if the control factor is located in the second range; and executing a normal mode if the control factor is not located in the first range and the second range.

Abstract: A control method of a fan rotation speed, which controls the operation of a fan set including fans connected in series, is disclosed. The control method includes the steps of acquiring a control factor; judging whether the control factor is less than a first threshold value; executing a first control procedure when the control factor is less than the first threshold value; judging whether the control factor is greater than a second threshold value when the control factor is greater than the first threshold; executing a second control procedure when the control factor is greater than the second threshold value; and executing a third control procedure when the control factor is less than the second threshold value.

Abstract: A fan system includes a driving device, a speed detecting device and a logic device. The driving device generates a speed detecting signal and a predetermined alarm signal. The speed detecting device, which is electrically connected with the driving device, receives the speed detecting signal, and generates a low speed signal when the speed detecting signal is lower than a reference signal. The logic device is respectively electrically connected with the driving device and the speed detecting device, and generates an alarm signal when the logic device receives the predetermined alarm signal or the low speed signal.

Abstract: A motor control circuit includes a pulse width modulation (PWM) signal generating circuit, a driving circuit and a waveform-shaping circuit connected between the PWM signal generating circuit and the driving circuit. The PWM signal generating circuit generates a square wave with a sequence of alternating on-time and off-time. The waveform-shaping circuit adjusts the rise-time and the fall-time of the square wave to be both within a range of 5% to 15% of the square wave period, and the driving circuit outputs a driving signal to a fan motor according to the adjusted square wave.

Abstract: A heat dissipation device comprises a fan motor, a drive circuit, and a reset current reduction circuit. When the fan motor is locked, an input terminal of the reset current reduction circuit receives an alarm signal, and an output terminal thereof outputs a voltage signal, which is larger than a reference voltage generated as the fan motor is at a low rotation rate, so as to decrease a reset current of the fan motor.

Abstract: A motor control circuit includes a pulse width modulation (PWM) signal generating circuit, a driving circuit and a waveform-shaping circuit connected between the PWM signal generating circuit and the driving circuit. The PWM signal generating circuit generates a square wave with a sequence of alternating on-time and off-time. The waveform-shaping circuit adjusts the rise-time and the fall-time of the square wave to be both within a range of 5% to 15% of the square wave period, and the driving circuit outputs a driving signal to a fan motor according to the adjusted square wave.

Abstract: A motor control circuit includes a pulse width modulation (PWM) signal generating circuit, a driving circuit and a waveform-shaping circuit connected between the PWM signal generating circuit and the driving circuit. The PWM signal generating circuit generates a square wave with a sequence of alternating on-time and off-time. The waveform-shaping circuit adjusts the rise-time and the fall-time of the square wave to be both within a range of 5% to 15% of the square wave period, and the driving circuit outputs a driving signal to a fan motor according to the adjusted square wave.

Abstract: A fan system includes a driving device, a speed detecting device and a logic device. The driving device generates a speed detecting signal and a predetermined alarm signal. The speed detecting device, which is electrically connected with the driving device, receives the speed detecting signal, and generates a low speed signal when the speed detecting signal is lower than a reference signal. The logic device is respectively electrically connected with the driving device and the speed detecting device, and generates an alarm signal when the logic device receives the predetermined alarm signal or the low speed signal.

Abstract: A fan speed control circuit includes a pulse width modulation (PWM) signal generating circuit, a driving circuit and a phase compensation unit. The PWM signal generating circuit generates a PWM control signal with a sequence of alternating on-time and off-time, and the driving circuit outputs a driving signal according to the PWM control signal to a fan motor. The phase compensation unit is connected to the fan motor for delaying or advancing the PWM control signal by a phase angle to synchronize the acting period of the back electromotive force formed by the magnetic flux variation with the off-time of the PWM control signal.

Abstract: A fan control device receives a reference revolution signal to control the rotation speed of a fan. The fan control device includes a reference signal generating module, a revolution modifying module and a fan driving module. The reference signal generating module generates a first reference signal and a second reference signal. The revolution modifying module receives the first reference signal and the second reference signal, and generates a target revolution signal according to the reference revolution signal and the first and second reference signals. The fan driving module receives the target revolution signal and generates a driving signal to drive the fan according to the target revolution signal.