Introduction / Context:
Zener diodes are specially doped semiconductor diodes designed to operate in the breakdown region safely. They are ubiquitous in power supplies, reference modules, and protection networks. This question tests conceptual understanding of how Zener breakdown is used to hold a nearly constant voltage across a load despite changes in input voltage or load current.
Given Data / Assumptions:
- The Zener diode is reverse-biased during normal operation.
- It exhibits a sharp breakdown at the Zener voltage Vz and maintains an approximately constant voltage there.
- Series resistance is used to limit current to a safe value.
Concept / Approach:
The key feature is the diode’s near-constant voltage in breakdown (Zener and/or avalanche mechanisms). By placing the Zener diode in shunt with the load and using a series resistor from an unregulated source, the Zener clamps the output at Vout ≈ Vz, thus regulating the supply to the load even if the source varies within limits.
Step-by-Step Solution:
Place Zener diode in reverse across the load; choose Vz equal to desired regulated voltage.Use a series resistor Rs from the unregulated input Vs to limit current.Design inequality: IZ(min) ≤ IZ ≤ IZ(max). Load current IL plus Zener current IZ flows through Rs.Output voltage is held at Vout ≈ Vz as long as IZ stays within its safe operating range.
Verification / Alternative check:
Compute Rs = (Vs(min) − Vz)/(IL(max) + IZ(min)) to ensure regulation at worst case. Check power: Pz = Vz * IZ(max).
Why Other Options Are Wrong:
Amplifier circuits: a Zener does not provide gain; it is a reference/clamp, not an amplifying element.Both voltage regulator and amplifier: incorrect because a Zener is not used as a linear gain device.None of the above: false since regulation is the canonical application.Precision rectifier: implemented with op-amps and diodes, not a Zener function.
Common Pitfalls:
Confusing forward diode drops with Zener regulation in reverse breakdown.Ignoring current and power ratings of the Zener and series resistor.
Final Answer:
voltage regulator circuit
Discussion & Comments