How to make a computer quiet. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Computers

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A serious disadvantage of modern computers is that they are relatively noisy. One has only to be surprised at the periodically arising disputes about the nuances of the sound of a particular computer speaker system, if the noise level of the system unit does not fall below 30 ... 40 dB. The decisive contribution to this noise is made by the fans of the power supply and the microprocessor. You can partially solve the problem by replacing cheap fans with more expensive ones, but really low-noise coolers from well-known companies in Russia are not so easy to get, and they will last no more than half a year - during this time the bearings will still loosen up. Meanwhile, it is not so difficult to significantly reduce the noise level and at the same time extend the life of the fan - it is enough to integrate the automatic speed controller described below into the computer system unit.

A schematic diagram of a device that regulates the fan speed depending on temperature is shown in the figure.

Since there are at least two fans in the computer, it contains two independent channels, each made on one of the op amps included in the MAX478 chip from MAXIM. The choice of this relatively expensive microcircuit is due to the fact that its op amps make it possible to fully use the supply voltage range and are not prone to self-excitation at any gain and switching options.

Consider, for example, the operation of the upper (according to the scheme) regulator (A1), designed to control the speed of the power supply fan. The 1RK1 temperature sensor is a thermistor glued to the surface of the cooling heat sink. The fan is connected to the output of the emitter follower on the transistor 1VT1. As the temperature rises, the resistance of the thermistor decreases, the voltage at the output of the emitter follower rises, and, consequently, the fan speed increases. The device is configured in such a way that at a heat sink temperature of about +60 ° С (during normal operation it should not exceed +40 ... 50 ° С), the fan supply voltage reaches 9,5 ... 10,2 V (the circuit will not allow output stage op-amp DA1.1 - emitter follower 1VT1 - diode 1VD1).

If the temperature continues to increase, the emergency switch-on assembly is activated, assembled on resistors 1R2, 1R3, transistor 1VT2 and relay 1K1. When the set threshold is exceeded, the transistor opens and the relay contacts connect the fan directly to the +12 V power bus. At the same time, the device "latches" - it can only be removed from this state by turning off the power. If you want to avoid "latching", connect the 1R2 resistor directly to the emitter terminal of the 1VT1 transistor. Diode 1VD1 protects the output of the op-amp from a short circuit to the power bus, capacitor 1C1 prevents accidental operation of the emergency switching unit in the presence of interference.

The second half of the device (A2) differs from that considered by the presence of the initial start capacitor C1 and the division of the upper resistor of the zero setting divider into two (R4 and R5). The fact is that the fan motor has a certain startup threshold, and individual motherboards may not start at all if the processor fan is not spinning (the signal comes from the yellow fan wire). Capacitor C1 is discharged when the power is turned on and at the first moment closes resistor R5, as a result of which an increased voltage is applied to the fan, sufficient to start. If this is not critical, it is better to remove the capacitor C4, and combine the resistors R4 and R5 into one, as in the first regulator.

Thermistors of any type can be used in the device, however, it is desirable that their cases have a flat surface to ensure reliable thermal contact when glued to a cooling heat sink, and the resistance at +25 ° C is at least several kiloohms. The nominal resistance of the feedback resistor 1R1 (2R1) should be 2...3 times this value.

Transistors 1VT1 and 2VT1 - KT815G or KT815B with a static current transfer ratio of at least 100. Relays - any small-sized ones with a response voltage of not more than 12 V (the author used a RES49 relay of RS4.569.421-08 version). All resistors - MLT or C1-4, diodes - any with a direct current of at least 200 mA, oxide capacitors - K50-35. In the absence of MAX478, it is permissible to use the domestic two-channel OU K140UD20. When self-excited, ceramic capacitors with a capacity of 1 ... 1 μF should be connected in parallel with resistors 2R1 and 1R2.

The device is assembled on a printed circuit or breadboard with dimensions of approximately 30x100 mm. To avoid trouble, you should install an already configured device into your computer. First, measure the voltage of the 12-volt source in the system unit under load (thick yellow wire). Usually it is equal to + 12,1 ... 12,2 V. Having set exactly the same voltage at the output of the laboratory power source (it must be stabilized), connect the regulator to it, temporarily disconnecting the resistors 1R2 and 2R2 of the emergency switch dividers and the capacitor; C1 start-up systems.

Before adjusting, the thermistor leads are insulated with some kind of dielectric varnish. After it dries, the thermistor is placed in water with room temperature (it is controlled by a household thermometer) and a trimmer resistor R2 is set to a voltage of about 1 V on the emitter of the 1VT3,5 transistor (this approximately corresponds to the fan stop threshold; it is better, of course, to carry out the setting with the fan connected). Then the thermistor is placed in water with a temperature of +55 ... 60 ° C and, by selecting a feedback resistor 1R1, a voltage of about 1 V is set on the 1VT9,5 emitter. This procedure is repeated several times until the desired values ​​\uXNUMXb\uXNUMXbare obtained at both temperatures.

After that, the fan emergency switch divider is connected and, having immersed the thermistor in water with a temperature above +60 ° C, the 1R3 resistor is selected so that the emergency switch unit operates at a voltage of 9,5 ... 10 V.

The second regulator is set up in the same way (the voltage at the emitter of the 2VT1 transistor is set by the trimming resistor R6 and the selection of the 2R1 resistor). Finally, if necessary, connect the capacitor C1 and check the performance of the device as a whole.

A debugged device is installed anywhere in the computer system unit away from heat-producing parts. Then, having opened the power supply, remove its board, unsolder the red fan wire from it and solder the +12 V regulator power wire instead. The red wire is connected to the output of the regulator, and the common wire is firmly fixed under any screw that has contact with the system unit case. The 1RK1 thermistor is securely glued to the largest heat sink of the block on a flat surface, as close as possible to the transistor, or glued between the heat sink fins (reliability of thermal contact is a determining part of success!). The wires connecting the thermistor to the regulator are taken out of the power supply in the same bundle with the standard ones.

Then mount the 2RK1 sensor on the heat sink of the microprocessor, bite off the red wire of the fan directly at the connector and connect it to the output of the second regulator.

The performance of the described device was tested on a system with a Celeron-633 processor and a 230 W power supply in an ATX mini-tower case. At a room temperature of +20°C, the voltage on the microprocessor fan did not exceed 6 V, and on the power supply fan - 7,5 V. Of course, with other characteristics of the system, cooling elements and case design, the voltage may be different.

Author: Yu.Revich, Moscow

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