Triggering modes of TRIAC (Triode for alternating current)

The following are the triggering modes of TRIAC (Triode for alternating current).

I ⁺ mode : The ‘I’ indicates first quadrant operation. The MT₂ (main terminal 2) positive with respect to MT₁ (main terminal 1). The ‘+’ symbol shows the polarity of gate (G) with respect to MT₁ (main terminal 1). In this mode the conduction of current takes place from MT₂ to MT₁.
I ^– mode : The ‘-’ shows the polarity of gate (G) with respect to MT₁ (main terminal 1). The conduction of current takes place from MT₂ to MT₁.
III ⁺ mode : The ‘III’ indicates the third quadrant operation where MT₁ (main terminal 1) is positive with respect to MT₂ (main terminal 2). The ‘+’ symbol shows the polarity of gate with respect to MT₁ (main terminal 1). The conduction of current takes place from MT₁to MT₂.
III ^– mode : The ‘-’ symbol shows the polarity of gate (G) with respect to MT₁ (main terminal 1). The conduction of current takes place from MT₁ to MT₁.