Shockley diode application in power electronics A Shockley diode (four-layer diode) is best used for which of the following purposes?

Introduction / Context:
Shockley diodes are two-terminal four-layer devices exhibiting a negative-resistance region and snap-action switching. They are historically used in triggering circuits rather than as main controllable power switches. Understanding the correct use case prevents design errors in gate-drive and protection circuits.

Given Data / Assumptions:

• Two-terminal, no gate control (unlike SCRs).
• Breakover behavior similar to a DIAC-like action (though different structures exist).
• Focus on practical triggering of SCRs or similar devices.

Concept / Approach:

An SCR requires a controlled gate current pulse to turn on at the intended instant. A Shockley diode can build up voltage across a timing capacitor and then snap to conduction at a predictable breakover voltage, providing a sharp current pulse to the gate of an SCR (or TRIAC with suitable interface).

Step-by-Step Solution:

Verification / Alternative check:

Textbook gate-drive circuits for SCRs frequently show DIAC/Shockley-like elements as triggers in phase-controlled rectifiers and lamp dimmers (with proper ratings).

Why Other Options Are Wrong:

Not a replacement for SCRs (no gate terminal and poor controllability). Not a linear amplifier. Not universally a substitute for a UJT oscillator (different characteristics and adjustability).

Common Pitfalls:

Assuming any four-layer device is interchangeable with an SCR; ignoring the lack of a separate gate terminal leads to control issues.

Final Answer:

As a trigger switch to fire an SCR