FAN CONTROL CIRCUIT AND SYSTEM
A fan control circuit for controlling a two-wire or three wire fan in a fan control system includes: a rotational speed detecting module, for detecting a rotational speed of the fan, in order to generate a rotational speed signal; a rotational speed converting module, coupled to the rotational speed detecting module, for converting the rotational speed signal into a first voltage signal; and a feedback control module, coupled to the rotational speed converting module, for generating a fan control signal to control the fan according to the first voltage signal.
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1. Field of the Invention
The present invention relates to a fan control circuit and system, and more particularly, to a fan control circuit and a related fan control system for controlling a two-wire or three-wire fan, wherein the fan control circuit and the fan control system are capable of controlling a rotational speed of the fan by detecting the rotational speed and integrating an external control signal using a signal integrating device.
2. Description of the Prior Art
Fans are widely applied in computer systems for heat dissipation. A fan can be divided into three types: four-wire, three-wire and two-wire. The four-wire fan has four pins: power, ground, tachometer and pulse width modulation (PWM) input, where the power pin is for providing power for the fan to operate, the tachometer pin is for detecting rotational speed information of the fan, and the PWM input pin controls rotational speed of the fan via a PWM signal. The three-wire fan has three pins: power, ground and tachometer, where the power pin replaces the function of PWM input, and controls rotational speed of the fan by varying the DC voltage, and the function of the tachometer pin is similar to that of the tachometer pin in the four-wire fan. The two-wire fan has two pins: power and ground, where the DC voltage of the power pin can also be varied to control the rotational speed of the fan. Since there is no tachometer pin in the two-wire fan, the rotational speed information of the fan cannot be measured and obtained by connecting a tachometer.
In a four-wire fan (which has both the PWM signal and the tachometer signal), the system may obtain the rotational speed information via the tachometer and control the rotational speed of the four-wire fan via the PWM signal. A feedback system is generated, where the PWM input pin and the power pin are utilized for controlling the rotational speed of the fan according to the rotational speed information obtained by the tachometer and an ambient temperature information, respectively. Please refer to
The fan control system 10 is formed by two loops. One of the loops is a temperature loop, where the temperature sensor 106 detects the temperature of the system to obtain an ambient temperature Ta, and then outputs a temperature parametric signal VTemp to the selection device 112. The selection device 112 then outputs a control signal Vctrl to the clock generator 114. The clock generator 114 converts the control signal Vctrl to the pulse width modulation signal PWMctrl, in order to control the rotational speed of the four-wire fan 102. The other loop is an external control loop, where the external control module 108 obtains the rotational speed information FG, and then generates an external control signal PWMin. The modulation converting module 110 then converts the external control signal PWMin in PWM form to an external control voltage signal VPWM in voltage form to output to the selection device 112. Similarly, the selection device 112 outputs the control signal Vctrl to the clock generator 114. The clock generator 114 converts the control signal Vctrl to the pulse width modulation signal PWMctrl, in order to control the rotational speed of the four-wire fan 102. As a result, the selection device 112 generates the control signal Vctrl according to the temperature parametric signal VTemp and the external control voltage signal VPWM simultaneously.
Although the four-wire fan has more pins and more complete functions, the cost of the four-wire fan is higher than that of the two-wire or three-wire fan. If the two-wire or three-wire fan is required, the fan rotational speed cannot be controlled by the PWM input pin, and therefore the fan rotational speed cannot be controlled accurately by the system. Furthermore, in the four-wire fan control system 10, the DC voltage source 104 outputs the input voltage Vin with a fixed value to the four-wire fan 102. When other four-wire fans with different voltage specifications are utilized, the power supply has to be adjusted accordingly, which reduces the flexibility of utilization. Thus, there is a need for improvement over the prior art.
SUMMARY OF THE INVENTIONIt is therefore an objective of the present invention to provide a fan control circuit for controlling a two-wire or three-wire fan, which is capable of controlling the rotational speed of the two-wire or three-wire fan by detecting the rotational speed and integrating an external control signal via a signal integrating device.
The present invention discloses a fan control circuit for controlling a two-wire or three wire fan in a fan control system. The fan control circuit comprises: a rotational speed detecting module, for detecting a rotational speed of the fan, in order to generate a rotational speed signal; a rotational speed converting module, coupled to the rotational speed detecting module, for converting the rotational speed signal into a first voltage signal; and a feedback control module, coupled to the rotational speed converting module, for generating a fan control signal to control the fan according to the first voltage signal.
The present invention further discloses a fan control system, which comprises a two-wire or three-wire fan; and a fan control circuit for controlling the fan. The fan control circuit comprises: a rotational speed detecting module, for detecting a rotational speed of the fan, in order to generate a rotational speed signal; a rotational speed converting module, coupled to the rotational speed detecting module, for converting the rotational speed signal into a first voltage signal; and a feedback control module, coupled to the rotational speed converting module, for generating a fan control signal to control the fan according to the first voltage signal.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
Please refer to
Functions of the temperature sensor 206 are similar to those of the temperature sensor 106. The temperature sensor 206 is utilized for obtaining an ambient temperature Ta′ and outputting a temperature parametric signal VTemp′. Functions of the external control module 208 are also similar to those of the external control module 108, where the main difference is that the external control module 208 cannot obtain the rotational speed information via the tachometer pin directly. Functions of the modulation converting module 210 are also similar to those of the modulation converting module 110. The modulation converting module 210 converts an external control signal PWMin′ in pulse width modulation (PWM) form outputted by the external control module 208 into an external control voltage signal VPWM′ in voltage form. The rotational speed detecting module 216 may replace the function of tachometer in the four-wire and three-wire fan, and can be utilized for detecting the rotational speed of the two-wire fan 202, in order to output a rotational speed signal SRS. The rotational speed detecting module 216 may detect the rotational speed of the two-wire fan 202 through various methods. In some embodiments, the rotational speed detecting module 216 may detect the rotational speed of the two-wire fan 202 via the Hall Effect. According to the principle of the Hall Effect, a rotating fan may drive the magnetic field to vary. If a voltage or current is exerted in the magnetic field, the variation of the magnetic field may cause the voltage or current to vary accordingly, and the variation may be detected to obtain the rotational speed signal SRS. For an illustration of this, please refer to
The rotational speed converting module 218 converts the rotational speed signal SRS into a rotational speed voltage signal VRS. The signal integrating device 220 receives both the rotational speed voltage signal VRS and the external control voltage signal VPWM′, and generates an integrated voltage signal VPWM
Please note that the external control module 208 may not obtain the rotational speed information via the tachometer directly, as mentioned above. The external control module 208, however, still has to perform accurate control through other methods according to the rotational speed information of the two-wire fan 202. Please refer to
In detail, the rotational speed converting module 218 converts the rotational speed signal SRS into the rotational speed voltage signal VRS via a conversion table 418. The conversion table 418 may set the rotational speed signal SRS and the rotational speed voltage signal VRS to be in a direct ratio. The relationship between these two signals may also be set up in other manners according to system requirements, which is not limited herein. In some embodiments, a transistor 402 maybe coupled to an output terminal of the rotational speed detecting module 216, in order to output the rotational speed signal SRS. The two-wire fan 202 is monitored externally, in order to detect whether the two-wire fan 202 operates normally. When an abnormal condition occurs in the rotational speed of the two-wire fan 202, the system may control the two-wire fan 202 to stop operating, or turn the fan off. The modulation converting module 210 includes a comparator 404, a resistor R1 and a capacitor C1. The comparator 404 includes an input terminal coupled to the external control module 208, another input terminal which receives a reference voltage Vref, and an output terminal coupled to the signal integrating device 220. The reference voltage Vref may be set to a middle voltage between a higher voltage level and a lower voltage level of the external control signal PWMin′, such that the comparator 404 may perform charging or discharging on the external control voltage signal VPWM′ according to whether the external control signal PWMin′ is located in the higher voltage level or the lower voltage level. The resistor R1 and the capacitor C1 may be utilized for setting a correspondence between the duty cycle and the external control voltage signal VPWM′, in order to set a maximum value of the external control voltage signal VPWM′ outputted to the signal integrating device 220 (i.e. to control the maximum value of the external control voltage signal VPWM′ to correspond to a 100% duty cycle). The external control signal PWMin′ is converted into a current output via the comparator 404 and then converted into the external control voltage signal VPWM′ via the resistor R1; parameters of the comparator 404 or the resistor R1 can thereby be adjusted, in order to adjust a correspondence between the duty cycle and voltage in a conversion table 410. In an embodiment, the resistor R1 may be placed off-chip and designed as a variable resistor, so that the resistor R1 can be adjusted easily. Most commercially available fans have a minimum rotational speed; hence in some embodiments, a minimum rotational speed setting module 406 can be coupled to the signal integrating device 220, in order to clamp a lower limit of the external control voltage signal VPWM′, which further limits the minimum rotational speed of the two-wire fan 202.
According to the correspondence between the duty cycle of the external control signal PWMin′ and the external control voltage signal VPWM′ in the conversion table 410, and the correspondence between the rotational speed signal SRS and the rotational speed voltage signal VRS in the conversion table 418, a correspondence between the duty cycle of the external control signal PWMin′ and the rotational speed of the two-wire fan 202 may be obtained. Please refer to
The selection device 212 outputs the control signal Vctrl′ according to the temperature parametric signal VTemp′ and the integrated voltage signal VPWM
The spirit of the present invention is to control the rotational speed of the two-wire or three-wire fan by detecting the rotational speed of the fan and by integrating an external control signal via a signal integrating device. Those skilled in the art can make modifications and alterations accordingly. For example, in the conversion table shown in
In the prior art, the cost of the four-wire fan is higher than that of the two-wire or three-wire fan. If the two-wire or three-wire fan with lower cost is required, the fan rotational speed cannot be controlled by the PWM input pin, such that the fan rotational speed cannot be controlled accurately by the system. In the conventional four-wire fan control system, the DC voltage source outputs a fixed input voltage. When other four-wire fans with different voltage specification are utilized, the power supply has to be adjusted accordingly, which reduces the flexibility of utilization. In comparison, the fan control systems according to the present invention are capable of controlling a rotational speed of the two-wire or three-wire fan by detecting the rotational speed and integrating an external control signal via a signal integrating device. In addition, the DC-DC converter 214 provides flexibility for voltage conversion between the input and output voltages, such that flexibility of fan selection and power supply can be significantly enhanced. In comparison with the conventional fan control system, the present invention has significant improvements in terms of cost and utilization flexibility.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.
Claims
1. A fan control circuit for controlling a two-wire or three wire fan in a fan control system, the fan control circuit comprising:
- a rotational speed detecting module, for detecting a rotational speed of the fan, in order to generate a rotational speed signal;
- a rotational speed converting module, coupled to the rotational speed detecting module, for converting the rotational speed signal into a first voltage signal; and
- a feedback control module, coupled to the rotational speed converting module, for generating a fan control signal to control the fan according to the first voltage signal.
2. The fan control circuit of claim 1, further comprising a DC-DC converter, for converting the fan control signal to output a signal corresponding to a voltage specification of the fan.
3. The fan control circuit of claim 1, wherein the rotational speed signal is in a voltage form or a current form.
4. The fan control circuit of claim 1, wherein the fan control system further comprises a temperature sensor, for detecting an ambient temperature of the fan, in order to generate a temperature parametric signal.
5. The fan control circuit of claim 4, wherein the feedback control module is further coupled to the temperature sensor, in order to generate the fan control signal according to the temperature parametric signal.
6. The fan control circuit of claim 1, wherein the fan control system further comprises an external control module, for generating an external control signal to control the fan control circuit.
7. The fan control circuit of claim 6, wherein the external control signal is a pulse width modulation signal, and the fan control circuit further comprises a modulation converting module for converting the pulse width modulation signal into a second voltage signal.
8. The fan control circuit of claim 7, wherein the feedback control module is further coupled to the modulation converting module, in order to generate the fan control signal according to the second voltage signal.
9. The fan control circuit of claim. 8, wherein the fan control system further comprises a temperature sensor, for detecting an ambient temperature of the fan, in order to generate a temperature parametric signal.
10. The fan control circuit of claim 9, wherein the feedback control module is further coupled to the temperature sensor, in order to generate the fan control signal according to the temperature parametric signal.
11. The fan control circuit of claim 10, wherein the feedback control module comprises:
- a signal integrating device, for integrating the first voltage signal and the second voltage signal to generate a third voltage signal; and
- a selection device, for selecting one of the temperature parametric signal and the third voltage signal according to which has a greater voltage as a fourth voltage signal, and generating the fan control signal via the fourth voltage signal.
12. The fan control circuit of claim 11, wherein the signal integrating device comprises an operational amplifier, which comprises:
- a first input terminal, coupled to the rotational speed converting module, for receiving the first voltage signal;
- a second input terminal, coupled to the modulation converting module, for receiving the second voltage signal; and
- an output terminal, coupled to the selection device, for outputting the third voltage signal.
13. The fan control circuit of claim 7, wherein the modulation converting module adjusts a correspondence between the pulse width modulation signal and the second voltage signal according to a correspondence between the first voltage signal and the second voltage signal.
14. The fan control circuit of claim 1, wherein the fan control circuit further comprises a minimum rotational speed setting module, for limiting a minimum rotational speed of the fan.
15. A fan control system, comprising:
- a two-wire or three-wire fan; and
- a fan control circuit, for controlling the fan, the fan control circuit comprising: a rotational speed detecting module, for detecting a rotational speed of the fan, in order to generate a rotational speed signal; a rotational speed converting module, coupled to the rotational speed detecting module, for converting the rotational speed signal into a first voltage signal; and a feedback control module, coupled to the rotational speed converting module, for generating a fan control signal to control the fan according to the first voltage signal.
16. The fan control system of claim 15, further comprising a DC-DC converter, for converting the fan control signal to output a signal corresponding to a voltage specification of the fan.
17. The fan control system of claim 16, wherein the rotational speed signal is in a voltage form or a current form.
18. The fan control system of claim 15, further comprising a temperature sensor, for detecting an ambient temperature of the fan, in order to generate a temperature parametric signal.
19. The fan control system of claim 18, wherein the feedback control module is further coupled to the temperature sensor, in order to generate the fan control signal according to the temperature parametric signal.
20. The fan control system of claim 15, further comprising an external control module, for generating an external control signal to control the fan control circuit.
21. The fan control system of claim 20, wherein the external control signal is a pulse width modulation signal, and the fan control circuit further comprises a modulation converting module for converting the pulse width modulation signal into a second voltage signal.
22. The fan control system of claim 21, wherein the feedback control module is further coupled to the modulation converting module, in order to generate the fan control signal according to the second voltage signal.
23. The fan control system of claim 22, further comprising a temperature sensor, for detecting an ambient temperature of the fan, in order to generate a temperature parametric signal.
24. The fan control system of claim 23, wherein the feedback control module is further coupled to the temperature sensor, in order to generate the fan control signal according to the temperature parametric signal.
25. The fan control system of claim 24, wherein the feedback control module comprises:
- a signal integrating device, for integrating the first voltage signal and the second voltage signal to generate a third voltage signal; and
- a selection device, for selecting one of the temperature parametric signal and the third voltage signal according to which has a greater voltage as a fourth voltage signal, and generating the fan control signal via the fourth voltage signal.
26. The fan control system of claim 25, wherein the signal integrating device comprises an operational amplifier, which comprises:
- a first input terminal, coupled to the rotational speed converting module, for receiving the first voltage signal;
- a second input terminal, coupled to the modulation converting module, for receiving the second voltage signal; and
- an output terminal, coupled to the selection device, for outputting the third voltage signal.
27. The fan control system of claim 21, wherein the modulation converting module adjusts a correspondence between the pulse width modulation signal and the second voltage signal according to a correspondence between the first voltage signal and the second voltage signal.
28. The fan control system of claim 15, wherein the fan control circuit further comprises a minimum rotational speed setting module, for limiting a minimum rotational speed of the fan.
Type: Application
Filed: Mar 13, 2013
Publication Date: Jul 3, 2014
Applicant: ANPEC ELECTRONICS CORPORATION (Hsin-Chu)
Inventors: Ching-Feng Lai (Taipei City), Dong-Yi Liu (Miaoli County)
Application Number: 13/798,137
International Classification: F04D 27/00 (20060101);