Ham Amateur Radio Technician Practice Exam

What is the primary purpose of a filter capacitor in a power supply circuit?

1. Store energy

2. Regulate voltage

3. Reduce ripple voltage

4. Increase current capacity

The correct answer is: Reduce ripple voltage

The primary purpose of a filter capacitor in a power supply circuit is to reduce ripple voltage. When an AC voltage is rectified to produce DC, the output is not a smooth, continuous voltage; instead, it typically includes fluctuations or "ripple" due to the nature of the rectification process. A filter capacitor is connected across the output of the rectifier to smooth out these fluctuations. It does this by charging up when the voltage increases and discharging when the voltage decreases, effectively leveling out the voltage variations and thus reducing the ripple. This action provides a more stable DC voltage, which is crucial for the proper operation of electronic devices and circuits that depend on a consistent power supply. While filter capacitors may also play a role in energy storage and are part of broader voltage regulation efforts, their specific function in this context is to minimize the ripple voltage present after rectification.