I just ran into another fan control circuit I don't recognize.
It's a 5V DC fan, but it gets +12v DC power from the positive leg of the power supply.
Looks like the ground is going through an IC of some sort. I have two units with different markings for the IC: JC1A or I(or J or L)1A
SOT-23 package.
Pin 1 of the IC goes into a GPIO pin on the PSOC4 over a 2.2k 1% resistor.
Pin 2 goes to a PSOC4 VSS.
Pin 3 connects to the fan motor and a 100uF 25V radial capacitor.
The fan only turns on when I apply heat to the SOT-23 IC (or in that general area). And when it does, I only see about 3V on the fan power pins, which is normal.
My initial thought was that it's just a simple fet and they control voltage to the fan with a PWM from the PSOC4.
But it doesn't seem to be the case as the fan only turns on when the heat is applied to the IC. Which makes me think that it might be a thermistor circuit of some kind.
Please point me in the right direction. Thank you!