Many applications using ... speed it can be represented by an inductor, resistor and power source. The back EMF, along with the RL circuit in a brushed DC motor, brings non-linearity to the PWM ...

the output of the 555 is connected to a MOSFET which is used to vary the speed of a computer fan motor. It’s an excellent way to learn about both PWM motor control and the use of 555 timers ...