I just built a fan speed controller, using the following schematic:
Now if you connect 12V from 555 and connect pin 7 to the blue CPU fan wire, it controls the speed, but whenever the PWM signal is approx 20% duty cycle, the fan runs approx 80% of full speed.
I liked the simplistic design and want to someday turn this into an LED dimmer. But I am not sure how to drive a N-channel FET or NPN transistor with the switched ground as opposed to the normal switched Vcc. How can I accomplish this?
Thanks for reading!