SCR gate drive practice: pulse triggering rationale Assertion (A): The gate current of an SCR is always applied in the form of pulses. Reason (R): With pulse triggering, gate losses are low.

Introduction / Context:
Gate-drive strategies for SCRs (thyristors) balance reliable turn-on against power dissipation and electromagnetic compatibility. While pulse triggering is common, it is not universally mandatory in all applications.

Given Data / Assumptions:

• Assertion claims “always pulses.”
• Reason claims pulse drive reduces average gate power (loss).
• Some DC circuits use continuous gate bias (e.g., for assured latching under marginal conditions).

Concept / Approach:
SCRs require a gate current above a threshold for a brief duration to transition to conduction, after which the gate can be removed. Pulse gating achieves this with minimal average gate power and reduced heating. However, continuous or long-duration gate drive is sometimes used (e.g., in noisy environments or when di/dt conditions are uncertain). Hence “always pulses” is too strong.

Step-by-Step Solution:
Evaluate A: Over-generalized; not always pulses → A is wrong.Evaluate R: Pulse drive indeed minimizes gate losses by limiting conduction time and average current → R is correct.Therefore the correct relationship is: A is wrong but R is correct.

Verification / Alternative check:
Manufacturer application notes describe both pulse and continuous gate techniques; pulse gating is preferred for efficiency but is not the only method used.

Why Other Options Are Wrong:

• Options assuming A is correct contradict practical designs using continuous gate drive.
• Both wrong: R is widely accepted as true.

Common Pitfalls:

• Equating “common practice” with “always required.”
• Ignoring cases with long gate pulse trains for noise immunity.

Final Answer:
A is wrong but R is correct