Question

How can we change the speed of a DC motor using PWM?

(a) By changing amplitude of PWM

(b) By keeping fixed duty cycle

(c) By changing duty cycle of PWM

(d) By increasing power of PWM

I had been asked this question during an interview.

The origin of the question is Interfacing with Motors in section 8051 Microcontroller of Microcontroller

Answer 1

Right choice is (c) By changing duty cycle of PWM

The best I can explain: We can change the speed of a DC motor using PWM by changing the duty cycle of PWM. Changing duty cycle means changing ON and OFF timing of PWM. Even if amplitude of PWM is fixed by increasing the ON time of PWM increases the speed of the DC motor.