Briefly describe how a voltage regulator maintains output voltage under varying load.

• A. It stabilizes the output by using a fixed resistor network.
• B. It varies the input voltage to match the load.
• C. It modulates output via a pass element, transformer, or switching to keep the output within a specified range under varying load.
• D. It stores energy in a capacitor bank without regulation.

Answer: (C)

A voltage regulator keeps the output steady by actively controlling the output stage based on feedback. It compares the actual output to a precise reference and uses that difference to adjust how the output is produced. That adjustment happens through a pass element in a linear regulator (a transistor in series with the load) or through switching circuitry in a switching regulator.

In a linear regulator, when the load draws more current and the output starts to drop, the regulator increases the transistor's conduction to push the voltage back up. If the load decreases, it reduces conduction to prevent the voltage from rising too high. In switching regulators, the regulator rapidly turns the switch on and off and varies the on-time (duty cycle) or uses a transformer in the power path to keep the average output voltage within tolerance, with filtering to smooth the output. Capacitors can help with transient response, but they don’t regulate on their own.