I think I saved the old blower
regulator from my car. Maybe it can be repaired?? So it would be a good candidate for you. I check it out and advise.
The use of an op-amp or comparator would result in precise switching point. In the graph above, there's a slope to the line. IE it takes about 30 deg change for the transistor to fully switch from ON to OFF (and vice versa).
This is because there's not enough gain in the transistor. An op-amp supplies the missing gain (voltae gain = 100,000 typ) at the threshold point.
But you still need the transistor to drive the fan and other extra parts (biasing resistors, bypass caps, filter caps, etc..).
I think that any blower regulator would work nicely. So if you have one, consider using it. I can help figure out the connections if you need help.
Regards . . . . JimF
'94 S500 Cpe
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