Difficulty: Easy
Correct Answer: Incorrect
Explanation:
Introduction / Context:
Simple shunt regulators are widely taught because they illustrate the concept of clamping a node voltage by diverting excess current to ground. However, terminology matters: which component is the “control element”? Distinguishing the reference function from the current-modulating element prevents confusion when students progress to series regulators and op-amp-based regulators.
Given Data / Assumptions:
Concept / Approach:
In a shunt regulator, the element that modulates current to maintain the node voltage is the shunt path itself. In the simplest circuit, the zener both provides the reference voltage and sinks current changes, but it is not called the “control element” in the same sense as the series pass element in a series regulator. When a transistor is added (zener referenced, transistor shunt), the transistor clearly becomes the control element while the zener remains the reference. Even in the bare-bones circuit, the more precise language is: the zener acts as a voltage reference and a current sink; it does not “control” the series current— the series resistor sets that—and regulation happens by shunting excess current.
Step-by-Step Solution:
Verification / Alternative check:
Data sheets specify zener “dynamic impedance” and knee current for proper regulation; series regulators, by contrast, specify pass-transistor control characteristics, highlighting the different roles.
Why Other Options Are Wrong:
Qualifiers about load level or knee current affect regulation quality, not the definition of which device is the control element. Adding a pass transistor changes topology; the original statement referred to a “basic shunt regulator.”
Common Pitfalls:
Calling the zener a “controller” rather than a reference/sink; ignoring the role of the series resistor that sets current available to be shunted.
Final Answer:
Incorrect
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