DC Fan Control – Converting PWM to Locked Rotor Signals

A short and simple post, which might come in handy for others in need of such an adapter. I’ve recently had a need to connect a 12V DC fan which has a RPM output (rotation speed measurement) to a device which was expecting a locked rotor signal instead. Since I needed this “right now”, and this is a very simple circuit after all, I’ve simply used whatever parts I’ve had laying around in the junk box to implement this. I’d like to share the schematic and explain the circuit, for these who might need such a circuit as well.

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