Turning off an SCR — gate removal vs commutation: “To turn an SCR off, simply remove the gate voltage.” Evaluate this statement in light of SCR latching behavior and holding current.

Introduction / Context:
Unlike transistors, SCRs latch on once triggered. Many beginners assume removing the gate signal will turn an SCR off. This question clarifies the correct turn-off mechanisms and prevents control-circuit mistakes.

Given Data / Assumptions:

• SCR is already conducting (latched).
• Gate current has ceased after triggering.
• Load and source support continuous current unless interrupted.

Concept / Approach:
An SCR remains on after triggering as long as its anode current exceeds the holding current. Removing gate drive does not force turn-off. To turn it off, the anode current must be reduced below the holding current—achieved naturally at AC zero crossings (natural commutation) or via forced commutation in DC circuits using auxiliary switches, capacitors, or inductors. Negative gate pulses may aid in special devices but are generally not relied upon for turn-off in standard SCRs.

Step-by-Step Solution:

Verification / Alternative check:
Textbook waveforms show the gate pulse only at the beginning of conduction; the device remains on without continuous gate drive and turns off at current zero or by commutation circuits.

Why Other Options Are Wrong:

• Correct: Incorrect; contradicts latching behavior.
• Valid only with negative gate bias: Not standard; most designs do not depend on reverse gating to turn off.
• True for TRIACs but not SCRs: TRIACs also latch; they turn off at current zero.
• Depends exclusively on ambient temperature: Temperature shifts thresholds slightly but not the basic mechanism.

Common Pitfalls:
Designing SCR controls like transistor drivers; forgetting holding/latching current concepts and commutation requirements.

Final Answer:
Incorrect