Fan speed controlling system

A fan speed controlling system for a power supply comprises a fan having two pins and a voltage comparator connected to the fan. The voltage comparator comprises a first input terminal for receiving a first reference voltage controlled by an external temperature of the power supply and a second input terminal for receiving a second reference voltage controlled by an interior temperature of the power supply. The voltage comparator outputs a higher voltage of the first and second reference voltage to the fan via the two pins.

FIELD OF THE INVENTION

The present invention relates to fan speed controlling systems, more particularly to a fan speed controlling system for a power supply of a computer.

DESCRIPTION OF RELATED ART

Computer systems generally include a power supply for providing voltage to the components in the computer. A fan is typically used with power supplies for preventing temperatures in the computer systems from becoming too high. Generally, the faster the fan speed is, the better a cooling effect is. However, fan speed greater than needed adds unnecessary noise to the environment and wastes energy. So, it is necessary to control the fan speed.

A conventional fan speed control method is using a two pins fan. The fan is connected to a voltage providing circuit providing a variable voltage according to the interior temperature of the power supply. When the temperature becomes higher, the voltage provided to the fan becomes higher too, and the fan rotates faster. When the temperature becomes lower, the voltage provided to the fan becomes lower too, and the fan speed becomes lower. However, the two pins fan is only able to adjust the fan speed according to the interior temperature of the power supply and not the exterior of the power supply. So, a four-pin pulse width modulation (PWM) fan is used in the industry. The PWM fan includes a fan speed testing circuit and a pulse width controlling circuit. The PWM fan speed can be controlled by both the interior and external temperature of the power supply. However, the PWM fan is of a complicated configuration and adds to the cost of manufacturing.

What is needed, therefore, is a fan speed controlling system of a less complicated nature wherein the fan speed can be controlled according to both the interior and external temperatures of the power supply.

SUMMARY OF THE INVENTION

A fan speed controlling system for a power supply comprises a fan having two pins and a voltage comparator connected to the fan. The voltage comparator comprises a first input terminal for receiving a first reference voltage controlled by an external temperature of the power supply and a second input terminal for receiving a second reference voltage controlled by an interior temperature of the power supply. The voltage comparator outputs a higher voltage of the first and second reference voltages to the fan via the two pins.

Other advantages and novel features will be drawn from the following detailed description of preferred embodiments with attached drawings, in which:

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawing, a fan speed controlling system in accordance with a preferred embodiment of the present invention, includes a temperature testing device10, a controlling device20(such as a BIOS of a computer), a digital/analog signal converter30, and a power supply40. The power supply40includes a voltage comparator43and a functional component like a fan44.

The temperature testing device10tests a temperature of the computer system and simultaneously outputs a temperature signal to the controlling device20.

The controlling device20receives the temperature signal from the temperature testing device10and outputs a corresponding variable digital control signal. The higher the temperature of the computer system is, the stronger the digital control signal is.

The digital/analog signal converter30is connected to the controlling device20for receiving the variable digital control signal and transforming it to a variable first reference voltage V1. The stronger the control signal is, the higher the first reference voltage V1is.

The power supply40includes a voltage providing circuit41producing a variable second reference voltage V2according to the temperature in the power supply40, the voltage comparator43, and the fan44. The voltage providing circuit41further includes a temperature sensor42for adjusting the second reference voltage V2. When the interior temperature of the power supply40goes up, the resistance of the temperature sensor42goes down, and thus the second reference voltage V2produced by the voltage providing circuit41goes up as well. Therefore, it follows that when the interior temperature goes down, the resistance goes up, and the voltage V2becomes lower.

The voltage comparator43includes a first input pin I1for receiving the first reference voltage V1output by the digital/analog signal converter30and a second input pin I2for receiving the second reference voltage V2output by the voltage providing circuit41. The voltage comparator43also includes a first output terminal O1and a second output terminal O2. The voltage from the second output terminal O2is zero. The voltage output from the first output terminal O1is the greater between the first and second reference voltage. That is, when the first reference voltage is higher than the second reference voltage, the voltage difference Vmax between the first output terminal O1and the second output terminal O2is equal to the first reference voltage V1; when the first reference voltage is lower than the second reference voltage, the voltage difference Vmax between the first output terminal O1and the second output terminal O2is equal to the second reference voltage V2.

The fan44includes a first pin1connected to the first output terminal O1of the voltage comparator43and a second pin2connected to the second output terminal O2of the voltage comparator43. The rotating speed of the fan44is always controlled by the higher of the voltages between the first reference voltage V1and the second reference voltage V2. Thus, the fan is maintained at an appropriate speed according to the greater of the temperatures of the interior and exterior of the power supply40.

It is to be understood, however, that even though numerous characteristics and advantages have been set forth in the foregoing description of preferred embodiments, together with details of the structures and functions of the preferred embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.