Help understanding fan controller circuit

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bitrex

Joined Dec 13, 2009
79
I'm looking at the circuit at http://sound.westhost.com/project42.htm. I understand that when the op amp output goes low, the transistor switches on the fan, and that it's controlled by the decrease in voltage drop across the diodes as they heat up, but I'm unclear as to how the op amp in that configuration works to detect the voltage change. Any help would be appreciated!
 

zhgart

Joined Dec 28, 2009
19
the op works at invetion mode. when the dirde heated up, the voltage on it will change (up or down depend on the feature of diode) r1 r2 pffer a bias current of diode. the diode voltage will be amp about 100times. that's all.
 
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