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This is a circuit to control the speed of fan using PWM signal.
Pin 4 is the input from controller which generates the PWM signal.
Pin 3 is the output from fan tachometer which provides the RPM to controller.
Pin 2 in power supply to the fan and pin 1 is the reference voltage.
"Can anyone please tell me what these two diode (D25 and D29) are doing here?"
Are they used to protect the circuit from back EMF or there is something else?
Please explain the use and working.
Thanks in advance