Power-supply filtering terminology: In a rectifier + filter DC power supply, the small residual AC component superimposed on the DC output is called what?

Introduction / Context:
After rectification and filtering, DC power supplies rarely produce perfectly steady voltage. A small periodic variation remains. Knowing the correct term and what it represents is foundational for power-supply design, specification reading, and troubleshooting.

Given Data / Assumptions:

• A rectifier converts AC to an unidirectional voltage.
• A capacitor or LC network smooths the waveform.
• Some periodic variation remains at the rectified frequency or its harmonics.

Concept / Approach:
The residual periodic variation on the DC output is called ripple. Its amplitude is often specified as peak-to-peak volts or as a percentage of the DC level. Ripple frequency is typically twice the mains frequency for full-wave rectifiers and equal to mains frequency for half-wave rectifiers (assuming a simple single-phase supply). Lower ripple is achieved with larger filter capacitance, lower load current, or additional RC/LC regulation stages.

Step-by-Step Solution:

Verification / Alternative check:
Inspect with an oscilloscope at the supply output: you will see a DC level with a periodic sawtooth-like or rounded ripple. Datasheets for regulators specify “ripple and noise” as a key parameter.

Why Other Options Are Wrong:

• Pulsating dc: Describes the raw rectified waveform before filtering, not the residual after filtering.
• Trickle: Informal term associated with low charging currents, not AC content on DC.
• Waffle: Not an electronics term.
• Hum offset: Informal phrasing; the technical term is ripple.

Common Pitfalls:
Confusing ripple with random noise; ripple is periodic and tied to rectifier frequency, while noise is broadband and often stochastic.

Final Answer:
ripple