Which device in the output stage acts as a power amplifier?

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

Answer: (C)

Power amplification means taking a small control signal and turning it into a larger power signal that can drive the load. In the output stage, the device that does this is a transistor. It takes a modest signal at its input (base or gate) and controls a much larger current from the supply to the load. That enables driving motors, heaters, or other actuators with the required power. A transistor can operate in its linear region to regulate output or be used as a switch in PWM schemes to deliver pulsed power with the right average value. The other concepts don’t provide this power-delivery role by themselves: an amplifier is a general term and may not handle the load power; PWM is a switching control method, not the power device; an On-Off controller is a control strategy, not a component that delivers variable power to the load.