Fan control device. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Electrician

Fan control device. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Electric motors

Sometimes in various electronic equipment it becomes necessary to control the operation of low-voltage fans. So, in my practice, it was necessary to control the correct operation of the coolers in DLP projectors, the failure of which, unnoticed in time, could lead to irreversible consequences. As a result, a simple device was developed that warns of the failure or stop of one of them before the temperature of the cooled module rises.

Using the device (Fig. 1), you can monitor the health of standard 12 and 24-volt fans (coolers), as well as low-power DC collector motors. The peculiarity of the device is that the signal is taken from the sensor, which is a self-resetting fuse F1. In a normal situation, the resistance of the fuse is small, so the voltage drop across it is small.

During the operation of both fans with an electronic driver and DC collector motors, short current pulses flow in their power circuit. During these pulses, voltage pulses appear on the self-restoring fuse F1, which are fed through the capacitor C1 to the base of the transistor VT1. Due to this capacitor based on the transistor, bipolar pulses are formed.

Fan control device
Rice. 1. Diagram of the device

The mode of operation of this transistor with the help of resistor R2 is chosen so that the voltage on its collector is about 1 V, so the capacitor C3 is charged through the diode VD2 to a voltage of fractions of a volt, the transistor VT2 remains closed and the HL1 LED is off. Transistor VT1 does not saturate and remains active. When the electric motor M1 is running, the transistor VT1 closes briefly with pulses of negative polarity, and at that moment a supply voltage appears on its collector, and the capacitor C3 is charged through the diode VD2 to a voltage of several volts. As a result, the transistor VT2 opens and the LED turns on. During the time between pulses, the capacitor C3 does not have time to discharge through the resistor R4, the transistor VT2 remains open and the LED shines constantly, signaling the health of the electric motor. Diode VD2 prevents the discharge of capacitor C3 through transistor VT1 when it is in the open state.

In the event of a break in the power supply circuit of the fan or its mechanical stop, the pulses do not arrive at the base of the transistor VT1, the capacitor C3 is discharged through the resistor R4. As a result, the transistor VT2 closes and the LED goes out, indicating a malfunction. The same thing happens with a short circuit in the fan power circuit. In this case, the fuse F1 is activated, its resistance increases sharply, and almost all the supply voltage is supplied to the resistor R1. Transistor VT1 goes into saturation, and capacitor C3 is not charged. Therefore, the transistor VT2 will be closed and the LED will be off until the fault is fixed. Capacitor C2 suppresses interference coming in this case from the positive power line.

All parts are placed on a single-sided printed circuit board, the drawing of which is shown in fig. 2. The appearance of the mounted board is shown in fig. 3. Fixed resistors are used - C2-23, P1-4, capacitors - small-sized ceramic or film. The VS546V transistor can be replaced with domestic transistors KT3102AM, KT3102BM, replacing the BS170 transistor - 2N7000, BS107 or KP501A (the latter has a different pinout). Diodes - any low-power rectifier or pulse, LED - low-power any color of glow with a case diameter of 3 ... 5 mm and a permissible current of 20 mA. Resettable fuses of the MF-R, RXE RUE, TR series can be used. The fuse operating current must be 1,5...2 times the rated current of the fan. In conclusion, it should be noted that the device was tested in the temperature range from -20 to +60 ^оWith and works flawlessly for more than ten years.

Fan control device
Rice. 2. Drawing of a printed circuit board and the location of elements on it

Fan control device
Rice. 3. Appearance of the mounted board

Author: D. Derr

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