Lead count comparison What are the total numbers of external leads for SCR, DIAC, and TRIAC respectively?

Introduction / Context:
Proper device identification and pin-out knowledge are foundational in power electronics. SCRs, DIACs, and TRIACs are common devices used for switching and control in AC and DC circuits.

Given Data / Assumptions:

• SCR: Silicon Controlled Rectifier (unidirectional).
• DIAC: Bidirectional trigger device with no gate terminal.
• TRIAC: Bidirectional thyristor used in AC control.

Concept / Approach:
SCRs have three terminals: anode (A), cathode (K), and gate (G). DIACs are two-terminal devices that switch at breakover in either polarity. TRIACs have three terminals: main terminal 1 (T1), main terminal 2 (T2), and gate (G).

Step-by-Step Solution:
Count terminals for SCR: A, K, G → 3.Count terminals for DIAC: two main terminals only → 2.Count terminals for TRIAC: T1, T2, G → 3.Hence, the sequence is 3, 2, 3.

Verification / Alternative check:
Datasheets and standard symbols confirm the terminal counts.

Why Other Options Are Wrong:

• Any option giving DIAC or TRIAC four terminals is wrong; DIAC has two, TRIAC has three.
• Swapping counts does not match device definitions.

Common Pitfalls:

• Confusing DIAC with TRIAC; DIAC is a trigger device, not a power switch.

Final Answer:
3, 2, 3