Editing TRIAC (section)

===Quadrant 4===
[[file:Triac Quad IV.svg|thumb|left|Figure 7: Operation in quadrant 4]]

Quadrant 4 operation occurs when the gate is positive and MT2 is negative with respect to MT1. <sup>[[#figure1|Figure 1]]</sup>

Triggering in this quadrant is similar to triggering in quadrant III. The process uses a remote gate control and is illustrated in Figure 7. As current flows from the p-layer under the gate into the n-layer under MT1, minority carriers in the form of free electrons are injected into the p-region and some of them are collected by the underlying n-p junction and pass into the adjoining n-region without recombining. As in the case of a triggering in quadrant III, this lowers the potential of the n-layer and turns on the PNP transistor formed by the n-layer and the two p-layers next to it. The lower p-layer works as the collector of this PNP transistor and has its voltage heightened: this p-layer also acts as the base of an NPN transistor made up by the last three layers just over the MT2 terminal, which, in turn, gets activated. Therefore, the red arrow labeled with a "3" in Figure 6 shows the final conduction path of the current.<ref name="PowerElec"/>

Generally, this quadrant is the least sensitive of the four.<ref name="ThyristorTheory"/> In addition, some models of TRIACs (three-quadrant high commutation triacs named by different suppliers as "logic level", "snubberless" or "Hi-Com" types) cannot be triggered in this quadrant but only in the other three.