Series voltage regulator essentials — A basic series (linear) regulator must include which internal functional blocks to maintain a stable output?

Introduction:
Series (linear) regulators keep the output voltage constant by comparing a scaled sample of the output to a stable reference and adjusting a pass element to correct any error. Identifying the mandatory functional blocks clarifies how regulation is achieved and what distinguishes a regulator from a simple follower or resistor dropper.

Given Data / Assumptions:

• Regulator topology: series pass element between source and load.
• Feedback loop present.
• Goal: hold Vout steady against line and load changes.

Concept / Approach:

A precision reference (e.g., bandgap) provides a stable yardstick. An error detector (usually an op-amp/comparator) compares the sampled output to this reference and drives the pass device to minimize the error. The load is external and not a functional block of the regulator itself.

Step-by-Step Solution:

Verification / Alternative check:

Block diagrams of common linear regulators (e.g., 78xx, LM317) show a reference and an error amplifier controlling the pass device—both are fundamental elements.

Why Other Options Are Wrong:

• an error detector: Needed but incomplete without a reference.
• a load: External to the regulator; not an internal block.
• a reference voltage: Needed but alone cannot regulate without error detection and control.
• only a pass transistor: Lacks feedback; cannot regulate.

Common Pitfalls:

• Confusing line regulation (input changes) with load regulation (output current changes) and thinking different blocks are needed; both are handled by the same loop.
• Ignoring loop compensation, which affects stability but is separate from the core functional requirement.

Final Answer:

both an error detector and a reference voltage