This circuit is ideal to control the cooling fan of heat generated
electronic gadgets like power amplifiers. The circuit switches on a fan
if it senses a temperature above the set level. The fan automatically
turns off when the temperature returns to normal.
The circuit uses an NTC (Negative Temperature Coefficient) Thermister to
sense heat. NTC Thermister reduces its resistance when the temperature
in its vicinity increases.IC1 is used as a voltage comparator with two
potential dividers in its inputs. Resistor R1 and VR1 forms one
potential divider connected to the non inverting input of IC1 and
another potential divider comprising R2 and the 4.7K Thermister
supplying a variable voltage to the inverting input of IC1. VR1 is
adjusted so as to give slightly lesser voltage at the non inverting
input than the inverting input at room temperature.
DC Fan Controller Circuit
In this state, output of IC1 will be low and the Fan remains off. When
the temperature near the Thermister increases, its resistance decreases
and conducts. This drops the voltage at pin 2 of IC1 and its output
becomes high. T1 then triggers and fan turn on. Red LED indicates that
fan is running. Capacitor C1 gives a short lag before T1 turns on to
avoid false triggering and to give proper bias to T1.DC fan can be the
one used in Computer SMPS.
Keep the Thermistor near the heat sink of the Amplifier PCB and switch on the amplifier for 10 minutes. Then adjust VR1 till the Fan stop running.When the temperature rises, Fan will automatically switch on.
Keep the Thermistor near the heat sink of the Amplifier PCB and switch on the amplifier for 10 minutes. Then adjust VR1 till the Fan stop running.When the temperature rises, Fan will automatically switch on.
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