Which motor type provides simple speed control via voltage?

Which motor type provides simple speed control via voltage?

• A. DC motors
• B. Servo motors
• C. Stepper motors
• D. Induction motors

Answer: (A)

Controlling speed by adjusting the supply voltage is a natural fit for a DC motor. In brushed DC motors, the speed increases as voltage increases because back-EMF rises with speed and effectively reduces the net voltage across the winding, so the current (and torque) balance shifts to a higher speed. In other words, higher voltage lets the motor reach a faster operating point; lower voltage slows it down. In practice, this is often done with PWM to vary the average voltage smoothly and efficiently. Other motor types don’t respond to simple voltage changes in the same direct way: servos rely on feedback for precise position control, stepper motors advance in discrete steps based on pulse rate, and induction motors require changing the drive frequency (often with voltage adjustments) to control speed. So the straightforward, common way to achieve speed control via voltage is with a DC motor.

Controlling speed by adjusting the supply voltage is a natural fit for a DC motor. In brushed DC motors, the speed increases as voltage increases because back-EMF rises with speed and effectively reduces the net voltage across the winding, so the current (and torque) balance shifts to a higher speed. In other words, higher voltage lets the motor reach a faster operating point; lower voltage slows it down. In practice, this is often done with PWM to vary the average voltage smoothly and efficiently. Other motor types don’t respond to simple voltage changes in the same direct way: servos rely on feedback for precise position control, stepper motors advance in discrete steps based on pulse rate, and induction motors require changing the drive frequency (often with voltage adjustments) to control speed. So the straightforward, common way to achieve speed control via voltage is with a DC motor.