PC:n tuulettimen 'termostaatti'-kytkent„,
        lainattu EE:n numerosta july 92.

        Kirjoittanut EE:st„, Pasi Patama - Frantic System 93.

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        PC Cooling fan control - Elektor Electronics July -92

        ...
        The circuit, designed with discrete component, is intended for
        the control of 12v fans that do not draw current exceeding
        200mA.

        To ensure that the fan operates satisfactorily in all
        circumstances, the supply to it must not drop bellow its
        starting voltage. That voltage is equal to the 12v supply less
        the 'zener' voltage of T3-R6-R7. With values shown in the
        diagram, the supply to the fan will be at least 7v.
        If the fan does not start at 25øC, replace temperature sensor
        temporarily by a 1.8kê resistor and lower the value of R7. If
        the fan runs too fast, raise the value of R7.
        Transistors T1 and T2 compare the fixed potential at junction
        R3-R4 with the temperature-dependent one at junction R1-R2.
        It may be found convenient initially to place 25kê potentiometer
        in the R2 position, adjust this till the fan runs correctly,
        measure the resistance of that value.
        Place the temperature sensor in the warm air flow of the fan.
        When the computer is switched on, the speed of the fan, owing to
        C1, will be fairly high, but will soon drop to a minimum.
        With a thermometer, measure the temperature of the outflowing
        air close to the sensor. When the temperature has reached a
        value of about 35øC, the control circuit should come into
        action, indicated by an increase in the speed of the fan or it's
        supply voltage. If that does not happen, change the value of R2,
        or adjust the potentiometer in its place. When the temperature
        rises, the speed of the fan will increase.
        The maximum speed will be only slighly lower that that without
        the control circuit. This is thanks to the fact that T3 can be
        driven into hard conduction, so that the drop across it is only
        some thenths of a volt.

        (c) Elektor Electronics [K.Walraven - 924028]

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