LASCR internal structure A light-activated SCR (LASCR) contains how many semiconductor layers and junctions?
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A4 semiconductor layers and 3 junctions
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B3 semiconductor layers and 2 junctions
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C2 semiconductor layers and 2 junctions
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DAny of these depending on rating
Answer
Correct Answer: 4 semiconductor layers and 3 junctions
Explanation
Introduction / Context:The LASCR is an SCR that can be triggered by light impinging on its gate region. Despite the optical triggering method, the internal thyristor structure remains that of a conventional SCR.
Given Data / Assumptions:
- LASCR is a PNPN device (thyristor).
- Light generates carriers near the gate area to initiate conduction.
Concept / Approach:
The classic SCR comprises four layers (PNPN) and three junctions (J1, J2, J3). The LASCR leverages the same layered stack; the difference lies only in how turn-on is initiated (photons instead of, or in addition to, electrical gate current).
Step-by-Step Solution:
SCR layering: P–N–P–N → 4 layers.Junctions: 3 (J1, J2, J3).LASCR: same structure, with an optical window or fiber coupling to gate region.Verification / Alternative check:
Datasheets specify LASCR gate sensitivity to light but list the same blocking ratings and junction structure as standard SCRs.
Why Other Options Are Wrong:
- 2- or 3-layer structures cannot provide thyristor-like latch characteristics.
- “Any of these depending on rating” is incorrect; ratings change geometry, not the fundamental layer count.
Common Pitfalls:
Confusing photodiodes or phototransistors (different layer counts) with LASCRs.
Final Answer:
4 semiconductor layers and 3 junctions