Assertion–Reason on SUS and SBS devices Assertion (A): A silicon unilateral switch (SUS) is essentially a programmable unijunction transistor (PUT) with an internal avalanche (Zener) diode between gate and cathode. Reason (R): A silicon bilateral switch (SBS) incorporates two SUS devices connected in anti-parallel within one package.

Introduction / Context:
SUS and SBS are low-power triggering components widely used in phase-control and timing circuits. Understanding their internal structure clarifies how they are applied for symmetrical or unilateral triggering in AC controllers and thyristor gate drives.

Given Data / Assumptions:

• SUS: a PUT-like device with a built-in Zener (avalanche) reference from gate to cathode to establish a defined breakover.
• SBS: two SUS-like junction structures arranged for bilateral (both-polarity) behavior.
• Assertion and Reason given as above.

Concept / Approach:

The SUS behaves like a PUT whose trigger point is set by an integrated Zener between gate and cathode, ensuring a repeatable breakover voltage in one polarity. The SBS is designed for symmetrical conduction; the common description is two SUS devices in anti-parallel, providing matched breakover in positive and negative directions.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturers’ datasheets and textbooks show SUS as a PUT derivative and SBS as a symmetric switch (bilateral breakover), confirming both statements independently.

Why Other Options Are Wrong:

• A true/R false: R is not false—SBS is indeed two SUS in anti-parallel.
• A false/R true: A is factual; SUS uses internal Zener referencing.
• “R explains A”: incorrect because R addresses SBS rather than the SUS internal Zener rationale.

Common Pitfalls:

Assuming SBS is just two ordinary diodes; it is a bilateral trigger built from SUS-like structures with matched characteristics.

Final Answer:

Both A and R are true but R is not correct explanation of A