Implementing a 3-input NAND logic function using thyristors A NAND gate has three inputs and one output. Approximately how many thyristors would be required to implement this function using SCR logic building blocks (ignore auxiliary components)?

Introduction / Context:
Thyristor logic circuits can implement digital functions by using SCRs as latching elements with steering networks. Realizing multi-input NAND behavior often requires one controlled path per input plus a combining or inversion stage, leading to variability in device count depending on the exact implementation (series/parallel logic and reset scheme).

Given Data / Assumptions:

• Three logic inputs; single output implementing NAND.
• Use of SCRs as the primary active elements.
• Auxiliary diodes/resistors are not counted.

Concept / Approach:

A 3-input NAND can be formed by combining AND then NOT, or by directly configuring SCRs so that output is inhibited only when all inputs are simultaneously asserted. Designs may require one SCR per input and a final stage to obtain the NAND inversion or to provide a latch/reset function, making the count 3 or sometimes 4 depending on whether a separate inverter/latch stage is used.

Step-by-Step Solution:

Verification / Alternative check:

Historic SCR logic implementations in industrial control demonstrate multiple realizations with slight variations in component count to meet noise margins and latching requirements.

Why Other Options Are Wrong:

• 1 or 2: insufficient to realize three-input gating and inversion robustly.
• Exactly 3: possible but not universal; often a fourth device is added for inversion/reset.

Common Pitfalls:

Forgetting that NAND requires inversion after an AND-equivalent network; overlooking the need for a latch or reset path in SCR logic.

Final Answer:

3 or 4