Power supplies — Regulation function: Providing a nearly constant output despite changes in AC input or load resistance is the function of which block?

Introduction / Context:
Modern power supplies are built from functional blocks: transformer, rectifier, filter, and regulator. Distinguishing their roles is crucial for design and troubleshooting. Regulation specifically means holding the DC output stable as input or load varies within limits.

Given Data / Assumptions:

• AC mains or AC secondary feeding a supply.
• Rectification and filtering produce a DC rail with residual ripple.
• A regulator stage adjusts to input/load changes to keep output constant.

Concept / Approach:

The regulator senses output and corrects for deviations using feedback or reference-based control (linear LDOs, series regulators, or switching regulators such as buck/boost). The transformer sets voltage level and isolation; the rectifier converts AC to pulsating DC; the filter smooths ripple; only the regulator enforces a constant output voltage or current target.

Step-by-Step Solution:

Verification / Alternative check:

Measure load regulation and line regulation: with a regulator, output change remains small over a range of line and load; without one, DC varies significantly with input and current draw.

Why Other Options Are Wrong:

• transformer: Sets AC level/isolation; does not regulate DC output.
• filter: Reduces ripple but cannot hold a setpoint under load or line changes.
• rectifier: Determines polarity and conversion to DC; not regulation.
• surge suppressor: Protects against spikes, not steady regulation.

Common Pitfalls:

• Assuming a large capacitor alone guarantees steady output; load changes still move the DC level without regulation.
• Ignoring thermal and dropout limits in linear regulators and duty-cycle limits in switching regulators.

Final Answer:

regulator