Editing TRIAC (section)

=== Quadrant 1 ===
{{multiple image
| total_width       = 400
| align             = left
| image1            = Triac Quad I.svg
| caption1          = Figure 3: Operation in quadrant 1
| image2            = Triac Quad I like SCR.JPG
| caption2          = Figure 4: Equivalent electric circuit for a TRIAC operating in quadrant 1
}}

Quadrant 1 operation occurs when the gate and MT2 are positive with respect to MT1.<sup>[[#figure1|Figure 1]]</sup>

The mechanism is illustrated in Figure 3. The gate current makes an equivalent NPN transistor switch on, which in turn draws current from the base of an equivalent PNP transistor, turning it on also. Part of the gate current (dotted line) is lost through the ohmic path across the p-silicon, flowing directly into MT1 without passing through the NPN transistor base.  In this case, the injection of holes in the p-silicon makes the stacked n, p and n layers beneath MT1 behave like a NPN transistor, which turns on due to the presence of a current in its base. This, in turn, causes the p, n and p layers over MT2 to behave like a PNP transistor, which turns on because its n-type base becomes forward-biased with respect to its emitter (MT2). Thus, the triggering scheme is the same as an SCR. The equivalent circuit is depicted in Figure 4.

However, the structure is different from SCRs. In particular, TRIAC always has a small current flowing directly from the gate to MT1 through the p-silicon without passing through the p-n junction between the base and the emitter of the equivalent NPN transistor. This current is indicated in Figure 3 by a dotted red line and is the reason why a TRIAC needs more gate current to turn on than a comparably rated SCR.<ref name="PowerElec"/>

Generally, this quadrant is the most sensitive of the four. This is because it is the only quadrant where gate current is injected directly into the base of one of the main device transistors.<ref>{{Cite web|title=TRIAC – Operation, symbol, circuits & applications|url=https://www.electricalclassroom.com/triac-operation-symbol-circuits/|website=Electrical Classroom|date=15 July 2021 }}</ref>