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In a thyristor (SCR), if the applied gate current is increased, what can be said about the anode current?

Difficulty: Medium

Correct Answer: Anode current may increase or decrease

Explanation:


Introduction / Context:
Thyristors are latching devices. The gate current influences turn-on behavior (latching current, turn-on time), but the steady anode current is set by the external circuit once the device is conducting. This question assesses that distinction.


Given Data / Assumptions:

  • Device: SCR operated in its forward-blocking to forward-conducting transition.
  • Gate current magnitude can be varied.
  • External anode circuit (source and load) determines current once latched.


Concept / Approach:
Increasing gate current reduces turn-on time and required latching/holding currents, so the device turns on more reliably and possibly earlier in a phase-controlled rectifier. However, the anode current after turn-on is governed by supply voltage, load impedance, and instantaneous waveform phase, not by the gate current (beyond the turn-on moment). Thus, depending on the circuit, average anode current may increase (earlier firing) or remain similar; generically, it may increase or decrease based on timing and load.


Step-by-Step Solution:

Gate current ↑ → improved triggering, lower latching/holding current thresholds.In phase control, earlier conduction → larger conduction angle → higher average anode current.In a DC chopper-like circuit with fixed ON timing already saturated, change may have little effect.Hence the safe, general statement: anode current may increase or decrease; it is not fixed by gate current alone.


Verification / Alternative check:

Datasheets indicate gate current affects di/dt limits and turn-on characteristics, not steady-state current for a given load line.


Why Other Options Are Wrong:

Always increase/decrease/constant: Overly absolute; ignores circuit dependence.Zero after turn-on: Contradicts the nature of conduction in an SCR.


Common Pitfalls:

Confusing control of a transistor's collector current via base current with an SCR's latching behavior.


Final Answer:

Anode current may increase or decrease
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