UMZCH cooling fan control device. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers
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In the magazine "Radio", 2008, No. 2 on p. 13 A. Zhurba's article "Power amplifier cooling fan control device" was published. Such a device has a significant drawback - during pauses in music programs, the fan continues to work for several seconds, producing significant acoustic noise, which is annoying.
The proposed device with a simpler scheme is devoid of this disadvantage. During pauses and at a low volume level, the fan runs at low speeds, making almost no noise. When the volume is increased, the fan turns on at full power, but its noise is now masked by an acoustic signal.
The device diagram is shown in the figure. It works in the following way. When the supply voltage is applied by the charging current of the capacitor C2, the engine M1 starts. Resistor R4, connected in series with the motor, reduces the voltage supplied to the motor and reduces its speed. The resistance of the resistor depends on the power of the engine and is selected experimentally according to the absence of acoustic noise during operation. With a sufficiently high voltage applied to the motor, capacitor C2 may not be needed.
The output voltage from the UMZCH is fed to the input of the device through the divider R1R2. Trimmer resistor R2 regulate the threshold of the device. The voltage of the audio signals rectified by the diode VD1 charges the capacitor C1 as their level increases. Through resistor R3, it discharges when the input signal level decreases. Zener diode VD2 limits the voltage applied to the gate at a safe level for transistor VT1.
When the threshold voltage level on the capacitor C1 is reached, the transistor opens, increasing the current through the motor to the nominal value. With a decrease in the output signal level of the UMZCH, the capacitor C1 quickly discharges through the resistor R3, the transistor closes and the motor M1 switches to work at low speeds. Diode VD3 protects the transistor from the load reaction (motor winding). If the motor is brushless, this diode can be omitted.
There are no special requirements for details, resistors and capacitors can be of any type. Diodes VD1 and VD3 - any low-power silicon, for example, KD509A, KD510A, D220. Zener diode VD2 - for a stabilization voltage of 7 ... 10 V, for example, D814A, KS175A. When the current consumed by the motor is more than 0,5 A, it is necessary to use a more powerful transistor, for example, IRFZ44N or domestic KP812A1.
The adjustment of the device consists in the selection of the resistor R4 to ensure the operation of the fan with an acceptable noise level and the capacitor C2 to reliably start the motor. When increasing the capacitance of the capacitor, it should be borne in mind that it is discharged through the low resistance of the drain-source transistor VT1, and in order to avoid damage to the transistor in series with a larger capacitor, it is advisable to include a resistor with a resistance of several ohms.
The device is assembled on a 10x20 mm segment of a universal breadboard and fixed near the fan.
Author: K. Moroz
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