Switch analogy — reverse bias behavior: Under typical operating conditions, does a reverse-biased diode behave like an open switch (very high impedance) until breakdown is reached?

Introduction / Context:
Diodes are often taught using a switch analogy: forward bias ≈ closed switch (low impedance), reverse bias ≈ open switch (high impedance). While this is a simplification, it is useful in understanding rectifiers, clamps, and protection circuits. The key caveats are reverse leakage at finite temperatures and eventual breakdown at sufficiently high reverse voltage.

Given Data / Assumptions:

• Standard p–n junction diode operated within ratings.
• Reverse voltage below the device’s breakdown rating (PIV).
• Temperature within normal range; leakage current is small but non-zero.

Concept / Approach:
In reverse bias, the depletion region widens, and only a tiny leakage current flows (reverse saturation current). Thus the diode presents a very high dynamic resistance, mimicking an open switch. If the reverse voltage exceeds the breakdown threshold (zener/avalanche), current rises sharply and the open-switch model no longer applies. Designers ensure normal operation stays well below breakdown unless using a zener intentionally for regulation.

Step-by-Step Solution:

Verification / Alternative check:
Use a DMM on resistance range: reverse direction reads very high resistance; forward direction reads low (or shows a diode drop in diode-test mode). Datasheets list typical reverse leakage (IR), confirming microamp-level currents at specified VR and temperature.

Why Other Options Are Wrong:
Restricting validity to specific diode types, voltages, or extreme temperatures is unnecessary. The open-switch approximation is widely applicable below breakdown for most silicon diodes.

Common Pitfalls:
Ignoring leakage in ultra-high-impedance nodes; in precision circuits, even microamps matter. Also, forgetting temperature dependence—leakage increases with heat.

Final Answer:
Correct