Device identification If two silicon unilateral switches (SUS) are connected in anti-parallel, which device is effectively realized?

Introduction / Context:Some solid-state trigger devices are constructed by combining simpler building blocks. A silicon bilateral switch (SBS) can be formed conceptually by arranging two silicon unilateral switches (SUS) in anti-parallel, giving symmetrical conduction characteristics for positive and negative polarities, useful in AC triggering (e.g., TRIAC gate drive).

Given Data / Assumptions:

• Two SUS devices are connected in anti-parallel.
• Goal: identify the resulting effective device behavior.

Concept / Approach:

A SUS is a unilateral device—it breaks over and conducts in one polarity only. Anti-parallel connection provides similar breakover behavior in both polarities, creating bilateral symmetry in I–V characteristics, which is the hallmark of an SBS.

Step-by-Step Solution:

Verification / Alternative check:

Data sheets for SBS devices highlight symmetrical breakover voltage and conduction in both polarities, aligning with anti-parallel SUS behavior.

Why Other Options Are Wrong:

• SCR: four-layer pnpn unilateral controlled rectifier, not achieved by simply anti-paralleling SUS.
• SCS: a gated variant of SCR; unrelated to bilateral symmetry here.
• UJT: a unijunction trigger device; does not result from anti-paralleling two SUS.

Common Pitfalls:

Confusing bilateral switching devices (SBS, TRIAC) with controlled rectifiers (SCR) that are inherently unilateral.

Final Answer:

SBS (silicon bilateral switch)