Computer fan control unit. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Computers

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The operation algorithm of the devices that control the cooling of the elements of the computer system unit, the descriptions of which have been published over the past few years, is approximately the same. As long as the temperature is not higher than the permissible one, the supply voltage reduced to 6,5 ... 7 V is supplied to the fans. At the same time, the cooling system, although it works less efficiently, is much less noisy. The voltage is usually reduced by including a resistor or a bipolar transistor in active mode in series with the fan supply circuit.

Unfortunately, in addition to its main purpose, this element limits the starting current of the fan motor. As a result, its mechanical starting torque decreases and, without overcoming static friction, the fan impeller may remain stationary when the computer is turned on. If the temperature exceeds the set one (usually 50 °C), the threshold device is activated and the fan supply voltage is increased to the nominal voltage (12 V). Until the temperature drops, the cooling system works harder. However, its maximum possible efficiency is still not achieved, since a significant part of the supply voltage drops on the switching element - a bipolar transistor.

In the proposed unit, the regulation of the voltage supplying the motors is carried out by the pulse method! Field-effect transistors with a very low (fraction of an ohm) open-state channel resistance were used as switching elements. They do not limit inrush currents, they practically do not reduce the supply voltage for fans running at full power.

The diagram of the computer fan control unit is shown in fig. 1. It has two independent control channels. The output of the first channel, assembled on DA1 and DA2 microcircuits and VT1, VT2 transistors, XP1 plug, to which a fan is connected that blows the processor heat sink. The second channel on the DA3 chip and the VT3 transistor serves other fans of the system unit, which are connected to the XP2 plug

On the integrated timers DA2 and DA3, the same pulse generators with a frequency of 10 ... 15 Hz are assembled. The charging and discharging circuits of the time-setting capacitors C1 and C2 (respectively, the first and second generators) are separated by diodes VD1-VD4, which allows you to adjust the duty cycle of the generated pulses with variable resistors R4 and R5. The pulses are fed to the gates of the field-effect transistors VT2 and VT3, the channels of which (with an open resistance of not more than 0,35 Ohm) are connected in series in the fan power circuit. By changing the duty cycle of the pulses, it is possible to adjust the rotational speed of the fan rotors over a very wide range while maintaining a sufficiently large starting torque. Due to the pulse mode of operation of field-effect transistors, the power dissipated by them is very small, which makes it possible not to install these transistors on heat sinks. Capacitors C5 and C6 smooth out the pulse drops, which eliminates the audible clicks in the fan motors that follow with a pulse repetition frequency. There is an additional node in the processor fan control channel that turns on this fan at full power if the temperature of the processor heatsink is above the allowed temperature. The node is built according to the well-known scheme on the OS DA1. The temperature sensor is the transistor VT1, mounted on the processor heat sink. The response temperature is set by a trimming resistor R7. The signal from the output of the op-amp DA1 is logically added to the generator pulses on the DA2 timer using diodes VD5 and VD6, as a result of which, when the permissible temperature is exceeded, the transistor VT2 is constantly open and the fan operates at full power.

The printed circuit board of the control unit is shown in fig. 2. It is designed for the installation of fixed resistors MLT-0,125, tuning SPZ-44 A (R 4, R 5) and SP 4-3 (R 7).

Capacitor C3-KM-6, the rest - oxide K50-35. Connectors XS1, XP1, XP2 - from faulty fans and motherboards. Instead of KR140UD708, you can use almost any op amp in a similar package, both domestic and imported. The KT315V transistor as a temperature sensor will replace any low-power silicon transistor of the n-p-n structure in a plastic case with a current transfer coefficient of at least 100. KP704A field-effect transistors can be replaced with imported n-channel low-resistance open channels, for example, IRF640 or IRF644. Instead of KD522 diodes, other low-power pulse diodes are suitable.

Preliminary adjustment of the control unit is most conveniently carried out in the laboratory. The engines of the trimmer resistors R4, R5, R7 are set to the extreme clockwise position. Fans are connected to the XP1, XP2 plugs, and a voltage source of 12 ± 0,1 V is connected to sockets 2 (+) and 1 (-) of the XS1 socket. When you turn on the power, the fans should start to rotate at maximum speed. Slowly turning the R 4 and R 5 trimming resistors counterclockwise, gradually reduce the fan speed and the noise generated by them. Continue decreasing the frequency until the bearing noise disappears. There will be only a slight noise generated by the fans of the air flow. Then check the node on the OS DA1. To do this, heat the transistor VT1 (temperature sensor) to approximately 40 ° C in any way possible, in extreme cases, holding the transistor with your fingers. Slowly turn the slider of the resistor R7 counterclockwise until the fan switches to the maximum speed and stop heating the sensor. After a few tens of seconds, the rotation frequency should abruptly decrease. This completes the preliminary adjustment of the control unit.

After installing the unit and the temperature sensor in the places intended for them in the computer system unit and connecting all the fans, turn on the computer to the network. Run any available temperature monitoring program for computer elements, monitor the temperature of the processor. Using the tuning resistor R7, ensure that the processor fan switches to maximum speed at a temperature of 50 ° C. After the temperature has dropped, use the tuning resistor R4 to set the fan speed so that, with an average processor load, the temperature of its case does not exceed 40 ° C. If at a room temperature of no more than 25 ... 28 ° C the processor fan often turns on at full power, you need to slightly increase the rotational speed first of the case fans, and then the processor fan. In many computer system units, not all the fans provided by the design are actually installed. It is recommended that you install them yourself if possible. This will increase the overall cooling efficiency at lower RPMs and provide an opportunity to get rid of the noise.

Author: S. Myatlev, g. Chapaevsk; Publication: cxem.net

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