Control of anode current in an SCR In a silicon-controlled rectifier (SCR), the anode current is ultimately determined by:

Introduction / Context:
The SCR is a latching device: a short gate pulse can switch it on, after which it remains on until the anode current falls below the holding current. Understanding the distinct roles of the gate and the external circuit is essential for reliable control and protection.

Given Data / Assumptions:

• Silicon PNPN device with latching and holding currents.
• Gate is used to trigger conduction; anode-cathode network provides current.

Concept / Approach:

Gate current influences the ease of triggering (reducing required anode-cathode voltage at turn-on and lowering delay). However, once the device is on, the anode current level is set by the external circuit: source voltage, load impedance, and any commutation components. The SCR remains conducting as long as anode current exceeds the holding current; therefore, both the gate action (for turn-on) and the external circuit (for current magnitude and turn-off conditions) determine behavior.

Step-by-Step Solution:

Verification / Alternative check:

Datasheets show gate-controlled turn-on curves and separate holding/latching current specs tied to the external circuit; designers size snubbers and series resistances accordingly.

Why Other Options Are Wrong:

(a) ignores external network; (b) ignores the need for gate trigger in a controlled rectifier; (d) is wrong because the external circuit still limits current; (e) device package has no control function.

Common Pitfalls:

Assuming gate current continuously controls conduction magnitude; in fact, after latching, the gate loses control until current falls below holding value.

Final Answer:

Both gate current and the external circuit