Assertion (A): Gate triggering is the most commonly used method to turn on a Silicon Controlled Rectifier (SCR). Reason (R): Even a small gate current is sufficient to drive an SCR into conduction (latching) and is easier to control than other methods such as dv/dt or thermal triggering. Choose the correct option about A and R.
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ABoth A and R are correct and R is the correct explanation of A
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BBoth A and R are correct but R is not the correct explanation of A
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CA is correct but R is wrong
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DA is wrong but R is correct
Answer
Correct Answer: Both A and R are correct and R is the correct explanation of A
Explanation
Introduction:Silicon Controlled Rectifiers (SCRs) are thyristor devices widely used in power control and conversion. Triggering methods include gate triggering, light triggering, dv/dt triggering, and thermal triggering. The question tests understanding of why gate triggering is preferred and whether a small gate current is sufficient to turn an SCR on.
Given Data / Assumptions:
- Device: SCR (thyristor)
- Gate terminal available for control
- Objective: evaluate correctness of Assertion (A) and Reason (R)
Concept / Approach:In practice, gate triggering is preferred because it is reliable, repeatable, and allows precise timing. The SCR requires a brief gate current pulse to create enough carriers to start conduction; once anode current exceeds the latching current, the device remains on without further gate drive.
Step-by-Step Solution:
1) Gate triggering is the industry standard: it uses low-power electronics and provides precise control over firing angle.2) A small gate current (above the specified I_G trigger) initiates conduction; after latching, the anode current maintains the ON state.3) Alternative methods like dv/dt or thermal are either undesirable (can cause false turn-on) or impractical for routine control.4) Therefore A is true. R states a key reason: small, easily generated gate current is sufficient, which directly supports why gate triggering is common.Verification / Alternative check:Datasheets specify I_GT (gate trigger current) typically in mA, confirming that modest pulses reliably fire SCRs under rated conditions.
Why Other Options Are Wrong:
- B: Suggests explanation is unrelated; it is directly related.
- C: R is not wrong; it reflects standard SCR behavior.
- D: A is not wrong; gate triggering is indeed the most common.
Common Pitfalls:Confusing holding current with latching current; assuming continuous gate drive is needed (it is not once latched).
Final Answer:Both A and R are correct and R is the correct explanation of A.