SCR conduction characteristics and junction temperature Assertion (A): When a silicon controlled rectifier (SCR) is conducting, the on-state voltage drop across it is approximately 1 V. Reason (R): When an SCR is conducting, the junction temperature is about 200°C.

Introduction / Context:
This item checks practical knowledge of SCR on-state behavior and allowable junction temperature. In power electronics design, knowing typical on-state voltage and realistic thermal limits is essential for loss and reliability calculations.

Given Data / Assumptions:

• Silicon controlled rectifier operating in on-state (conduction region).
• Normal current densities and adequate gate drive.
• Commercial device ratings and data-sheet conventions.

Concept / Approach:
In conduction, an SCR behaves like a forward-biased PNPN device with an on-state drop typically around 1 to 2 V depending on current and die temperature. Junction temperature ratings for most SCRs are commonly in the 110–150°C range; designing for ~125°C is typical. A blanket statement of “about 200°C” exceeds normal maximum junction ratings.

Step-by-Step Solution:
Check Assertion: On-state voltage ≈ 1 V to 2 V → “about 1 V” is acceptable as a typical value → A is correct.Check Reason: Typical Tj(max) is not 200°C; it is usually ≤ 150°C → R is false.Conclusion: A is true; R is false → Option “A is correct but R is wrong”.

Verification / Alternative check:
Representative SCR data sheets list V_T(on) ≈ 1.2–1.8 V at rated current and Tj(max) around 125–150°C. These corroborate A and contradict R.

Why Other Options Are Wrong:

• Options implying R is correct conflict with standard Tj ratings.
• “Both wrong” is invalid because the on-state drop statement is broadly correct.

Common Pitfalls:

• Confusing case temperature with junction temperature.
• Assuming on-state drop is negligible (it is not at high currents).

Final Answer:
A is correct but R is wrong