In PWM control of a DC motor, increasing the duty cycle has what effect?

• A. Decreases the average voltage to the motor.
• B. Keeps the average voltage constant.
• C. Increases the average voltage delivered to the motor.
• D. Only increases current without changing voltage.

Answer: (C)

PWM adjusts how long the supply is applied in each cycle. The motor sees a pulsed voltage, and with a high switching frequency and the motor’s inductance, the current responds to the average effect of those pulses. The average voltage across the motor is essentially the supply voltage multiplied by the duty cycle—the fraction of time the switch is ON. So, increasing the duty cycle raises this average voltage, which pushes more current through the windings and results in higher speed and torque (up to the limits of the motor and drive). The other ideas—that the average voltage stays the same, or that only current changes without changing voltage—don’t fit PWM behavior, since the duty cycle directly sets the average voltage delivered to the motor.