Power electronics component identification In a TRIAC (a bidirectional AC switch used in AC regulators and dimmers), the three external terminals are conventionally denoted as:

Introduction / Context:
A TRIAC is a three-terminal, bidirectional thyristor device widely used in AC power control (for example, lamp dimmers, heater controls, and single-phase motor speed control). Correctly identifying its terminals is essential for proper gate triggering, snubber placement, and reliable PCB layout.

Given Data / Assumptions:

• Device under discussion is a standard TRIAC.
• Common datasheet naming conventions are used.
• Terminal names are functional, not package-pin numbers.

Concept / Approach:
Unlike an SCR, which has an anode (A), cathode (K), and gate (G), a TRIAC conducts in both directions. Therefore, its two main terminals are not labeled anode/cathode. Instead, they are called main terminal 1 (T1) and main terminal 2 (T2). The third terminal is the gate (G), which can trigger conduction in either polarity quadrant of operation.

Step-by-Step Solution:
Recognize that bi-directional conduction prevents using anode/cathode naming.Industry-standard notation assigns T1 and T2 to the two power-carrying terminals.The control terminal remains the gate (G).Hence, the correct set is T1, T2, gate.

Verification / Alternative check:
Consulting any TRIAC datasheet (for example, BTA/BTB series) confirms terminal labels as T1, T2, and G, with triggering specified for four quadrants relative to T1/T2 polarities and gate reference.

Why Other Options Are Wrong:

• anode/cathode terminology applies to unidirectional SCRs, not TRIACs.
• T1, T2, anode includes a non-existent anode for TRIACs.
• T1, T2, T3 suggests three power terminals, which is incorrect.
• MT1/MT2 are synonyms for T1/T2, but “source” is not used for TRIACs.

Common Pitfalls:

• Miswiring T1 and T2 can change gate reference conditions and impair triggering.
• Assuming SCR anode/cathode naming for TRIACs leads to design errors.

Final Answer:
T1, T2, gate