Fan control circuit

1. Technical Field

The present disclosure relates to control circuits, and particularly to a fan control circuit.

2. Description of Related Art

In most computer systems, hardware controllers function as temperature monitoring elements, to transmit pulse width modulation (PWM) signals to adjust a rotation speed of fans, according to a temperature of the computer systems. However, if the hardware controllers operate abnormally and fail to transmit the PWM signals, the fans will stop running. Therefore, heat cannot be dissipated timely, which may affect normal operation of the computer systems and damage the computer systems.

Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the views.

The figure is a circuit diagram of an embodiment of a fan control circuit.

The disclosure, including the accompanying drawings, is illustrated by way of examples and not by way of limitation. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references can mean “at least one.”

The figure shows an embodiment of a fan control circuit 100 for controlling a rotation speed of a fan 80 . In one embodiment, the fan control circuit 100 includes a temperature sensor 10 , a central processing unit (CPU) 20 , a platform controller hub (PCH) 30 , a hardware controller 50 , a rectifier circuit 60 , three electronic switches Q 1 -Q 3 , four resistors R 2 -R 5 , and a light emitting diode (LED) D 2 . The rectifier circuit 60 includes a diode D 1 , a resistor R 1 , and a capacitor C 1 . The fan 80 includes a power pin VCC, a control pin PWM, a detecting pin TACH, and a ground pin GND. Each of the electronic switches Q 1 -Q 3 includes a first terminal, a second terminal, and a third terminal In one embodiment, the fan control circuit 100 is used in a computer system.

The CPU 20 is electrically connected to the temperature sensor 10 and the PCH 30 . The hardware controller 50 is electrically connected to the PCH 30 , an anode of the diode D 1 , the control pin PWM of the fan 80 , and the detecting pin TACH of the fan 80 . A cathode of the diode D 1 is grounded through the resistor R 1 and the capacitor C 1 in that order. The first terminal of the electronic switch Q 1 is electrically connected to a node between the resistor R 1 and the capacitor C 1 , and grounded through the resistor R 2 . The second terminal of the electronic switch Q 1 is electrically connected to a direct current (DC) power supply Vcc through the resistor R 3 . The third terminal of the electronic switch Q 1 is grounded. The first terminal of the electronic switch Q 2 is electrically connected to the second terminal of the electronic switch Q 1 . The second terminal of the electronic switch Q 2 is electrically connected to a cathode of the LED D 2 . The third terminal of the electronic switch Q 2 is grounded. An anode of the LED D 2 is electrically connected to the DC power supply Vcc through the resistor R 4 . The first terminal of the electronic switch Q 3 is electrically connected to the second terminal of the electronic switch Q 2 through the resistor R 5 . The second terminal of the electronic switch Q 3 is electrically connected to the control pin PWM of the fan 80 . The third terminal of the electronic switch Q 3 is electrically connected to the DC power supply Vcc. The power pin VCC of the fan 80 is electrically connected to a DC power supply 12V. The ground pin of the fan is grounded.

In use, the temperature sensor 10 senses a temperature of the computer system, and outputs the sensed temperature to the CPU 20 . The CPU 20 outputs a control signal to the hardware controller 50 through the PCH 30 according to the sensed temperature received from the temperature sensor 10 . If the hardware controller 50 operates normally, the hardware controller 50 outputs a pulse width modulation (PWM) signal having a duty cycle corresponding to the control signal to the rectifier circuit 60 and the control pin PWM of the fan 80 . The rectifier circuit 60 transforms the PWM signal into a DC voltage, and outputs the DC voltage to the first terminal of the electronic switch Q 1 . The electronic switch Q 1 is turned on after receiving the DC voltage output by the rectifier circuit 60 , and the electronic switches Q 2 and Q 3 are turned off. Thus, the LED D 2 is not lit up, which indicates that the hardware controller 50 operates normally. The rotation speed of the fan 80 is controlled by the PWM signal received from the hardware controller 50 .

If the hardware controller 50 does not operate normally and does not output the PWM signal, the rectifier circuit 60 does not output the DC voltage. Thus, the electronic switch Q 1 stays turned off, and the electronic switches Q 2 and Q 3 are turned on. When the electronic switches Q 2 and Q 3 are turned on, the LED D 2 is lit up to indicate that the hardware controller 50 does not output the PWM signal and should be repaired or replaced. Furthermore, when the switches Q 2 and Q 3 are turned on, the DC power supply Vcc supplies power to the control pin PWM of the fan 80 through the electronic switch Q 3 , so that the fan 80 rotates at full speed. Therefore, even if the hardware controller 50 does not output the PWM signal, the fan 80 continues to operate to dissipate heat from the computer system.

In one embodiment, each of the electronic switches Q 1 and Q 2 is an npn-type bipolar junction transistor (BJT), and the electronic switch Q 3 is a pnp-type BJT. The first terminal, the second terminal, and the third terminal of each of the electronic switches Q 1 and Q 2 are a base, a collector, and an emitter of the npn-type BJT, respectively. The first terminal, the second terminal, and the third terminal of the electronic switch Q 3 are a base, a collector, and an emitter of the pnp-type BJT, respectively. In other embodiments, each of the electronic switches Q 1 and Q 2 can be an n-channel metal-oxide semiconductor field-effect transistor or another type of electronic switch having similar functions. The electronic switch Q 3 can be a p-channel metal-oxide semiconductor field-effect transistor or another type of electronic switch having similar functions. The LED D 2 can be replaced by a buzzer or another type of indicator having similar functions. The LED D 2 can be omitted if power consumption and operation states of the hardware controller 50 are not essential to regulate.

Even though numerous characteristics and advantages of the disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.