SCR rated current versus holding current A thyristor (SCR) is rated at 40 A. Approximately what is the order of its holding current (Ih)?

Introduction / Context:
Holding current (Ih) is the minimum anode current below which a conducting SCR will turn off (cease conduction) when the external circuit allows it. It is crucial for commutation behavior and low-current turn-off in controlled rectifiers.

Given Data / Assumptions:

• SCR rated current = 40 A (continuous anode current rating).
• Typical power SCRs have holding currents in the tens to hundreds of milliamps range, much lower than their rated currents.

Concept / Approach:
In practical SCRs, latching and holding currents are small fractions of rated current. While exact values depend on device construction, a 40 A SCR commonly exhibits Ih on the order of 50–200 mA. Hence, 100 mA is a reasonable choice among the options.

Step-by-Step Solution:
Recognize Ih ≪ rated current for power SCRs.Select the option in the typical mA range: 100 mA.Exclude ampere-level values which are unrealistically high for Ih.

Verification / Alternative check:
Datasheets for SCRs in the 25–100 A class commonly specify Ih in tens to hundreds of milliamps, supporting the selection.

Why Other Options Are Wrong:
20 A / 4 A / 1 A: Far too high for holding current; these would make commutation impractical.
10 mA: Possible for smaller devices, but typically low for a 40 A device; 100 mA better matches typical power SCRs.

Common Pitfalls:
Confusing holding current with gate current or latching current; these are different specifications.

Final Answer:
100 mA