Which output signal conditioning element uses pulse width modulation to modify the voltage level?

• A. Saturation
• B. Transistor
• C. On-Off Controller
• D. PWM (Pump and Heater)

Answer: (D)

Pulse width modulation modifies the voltage that reaches a load by switching a fixed-amplitude signal on and off at a high frequency and changing how long it stays on in each cycle. The average voltage delivered to the load is the on-time fraction, or duty cycle, of the cycle, so by adjusting the duty cycle you control the effective voltage and thus the power to the device. This approach is ideal for devices like pumps and heaters because it provides smooth, adjustable control with high efficiency: the switching element dissipates little heat, unlike a linear regulator.

Saturation just clips a signal, so it can’t provide graded control. A transistor is a switching device used in PWM circuits but isn’t itself the modulation method. An On-Off Controller offers only full on or full off with no variable duty cycle.