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Do not use this circuit. The transistor will overheat. Yeah, it's pretty simple at this point. The op-amp is a schmitt-trigger to prevent oscillation, but this also means it toggles around the set temperature point instead of settling at a constant level. It's also abit simplified - there should be a buffer between the thermistor and the input to the op-amp. The transistor also needs a BIG heatsink, and possibly some current-limiting 10-20 ohm resistors as well. Don't underestimate the power dissipation values - run the numbers, or get burns on your thumb like me.The component values aren't too critical... the thermistor is 10K at 25'C and decreases as temperature rises, and the op-amp I used was an LM324 but just about anything could be used. |