Device exhibiting peak and valley points on its V–I characteristic Which device’s characteristic shows a distinct peak point followed by a valley point (negative-resistance region)?

Introduction / Context:
Some two-terminal or three-terminal devices exhibit a negative-resistance region where current rises as voltage drops. This region is characterized by a peak point (onset) and a valley point (near the low-voltage high-current state). Recognizing which devices show such behavior is key in triggering and relaxation-oscillator design.

Given Data / Assumptions:

• Comparing SCR, PUT, SCS, and Shockley diode.
• Focus on the presence of peak and valley points in the emitter/terminal characteristic.

Concept / Approach:

The classical device known for a peak and valley in its characteristic is the Unijunction Transistor (UJT). A PUT (Programmable UJT) is a PNPN device configured to emulate UJT-like behavior and also exhibits a programmable peak and valley point. The SCR and SCS have breakover and holding characteristics but are not generally described by peak/valley nomenclature in their common terminal curves.

Step-by-Step Solution:

Verification / Alternative check:

PUT data sheets and application notes (relaxation oscillators) explicitly specify peak current/voltage and valley current/voltage parameters.

Why Other Options Are Wrong:

SCR/SCS are four-layer switches with latching and holding currents; Shockley diode shows breakover rather than clearly defined peak and valley points used in UJT/PUT terminology.

Common Pitfalls:

Equating breakover and holding points of an SCR with the peak/valley description used for UJT/PUT emitter characteristics.

Final Answer:

PUT (Programmable Unijunction Transistor)