I was tired of fans running and full speed and causing lots of noise. For my self-made audio amplifier I designed thermocontrolled fans. Why to move air if you amp is playing calm music? The total amp output power is about 400W, but when playing normal music while surfing the net it uses only a fraction of power. The power amplifier is using modified ATX power supply for +-40V. The fan of PSU is moving always, but the radiator is only warm. And the radiators of the amplifier are hot as corpse’s arse.
Here is the schematics and PCB layout:
The details used in device are very regular, found in old AT and ATX power supply. Only one comparator used from LM339. Notes for schematics: R3 is NTC thermoresistor. Use R5 trimmer to adjust the fan start temperature. R3 must be connected to head source- radiator. R1 is used for hysteresis. Can be removed if R3 is in good thermal contact with radiator. C1 and C2 are only to remove possible false operations from power supply spikes of RFI. If C1 is big enough, it can be used to start the fan for few turns on power up. To move the oil 🙂 and to test if it is working. PCB to download.
It is linear FAN speed control, for more ecomonic way look at PWM fan speed control.
