SCR terminology — The holding current of a silicon-controlled rectifier (thyristor) is best defined as:

Introduction:
SCRs (thyristors) are latching devices used in controlled rectifiers and power controllers. Several current thresholds define their behavior: gate trigger current, latching current, and holding current. Correctly distinguishing these currents is essential for reliable turn-on and turn-off in practical circuits.

Given Data / Assumptions:

• Device: SCR operating in its intended quadrant.
• Once gated on and anode current flows, the device latches.
• Turn-off occurs when anode current falls sufficiently low.

Concept / Approach:

Holding current (I_H) is the minimum anode current below which the SCR will cease conduction and return to its blocking state. It is distinct from latching current (I_L), which is the minimum current needed immediately after triggering to establish conduction even if the gate signal is removed. After conduction is established, maintaining anode current above I_H keeps the SCR on.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets list both I_L and I_H, with I_H typically lower than I_L. Oscilloscope tests on SCR bridges show turn-off at current zero when I falls below I_H.

Why Other Options Are Wrong:

• minimum current required for turn-off: Misleading; turn-off occurs when current falls below I_H, but I_H is not a current you apply to turn off.
• current required before an SCR will turn on: Describes latching/trigger thresholds, not holding current.
• gate current required to maintain conduction: Gate current is not needed after latching.
• surge current rating: A transient limit, unrelated to holding behavior.

Common Pitfalls:

• Confusing I_L with I_H; remember I_L ≥ I_H and applies at the moment of turn-on.
• Assuming gate drive must be continuous; not true once latched.

Final Answer:

the amount of current required to maintain conduction