1. Define gate-current and main-terminal reference separately
A triggering quadrant combines two independent signs. One is the polarity of gate current relative to its stated reference; the other is the polarity of the voltage across the main device. ST's AN4363 explains the triac gate-current path with reference to A1. A description that says only positive drive leaves out which physical quantity and reference it means.
The main-terminal voltage can change polarity while the controller continues to supply gate current with the same sign. Conversely, a control architecture can make gate-current sign follow the main-voltage sign. These are different relationships between the two variables. Counting polarities without retaining their references would hide the relationship that defines the triggering quadrant.
Begin the comparison by identifying those functional references rather than assigning package terminals from a generic symbol. A gate-current direction is an electrical role, not a pin-number map. Once the references are clear, a required quadrant pair becomes understandable as a control-interface condition. It can then be compared with the applicable device-family evidence instead of being guessed from a supply name or a sensitivity category.
2. Treat usable quadrants as a device-family constraint
AN4363 does not give every named AC-switch family the same usable quadrant set. Its table describes standard ST triacs with four usable quadrants, while its named Snubberless and logic-level classes omit the fourth. The same table distinguishes ACS and ACST entries rather than grouping all protected AC switches under one triggering rule. AN4363's ACS discussion gives a concrete structural distinction: its gate-current path permits sinking rather than sourcing. That named example makes current direction more informative than a general AC-switch category.
That family distinction is useful because gate sensitivity and permissible polarity relationships answer different questions. A sensitivity description concerns the triggering requirement under its stated conditions; it does not independently establish that a family supports every quadrant the controller will use. A comparison retaining only sensitive gate could therefore discard an architectural restriction that remains relevant.
Use the family and class alongside the required quadrant set. The statement remains bounded to the devices and categories AN4363 actually describes; it should not become a universal rule for every supplier's similarly named product. This is a technical screening step before exact-device assessment, not a conclusion about current magnitude, mains suitability or a completed switching result. The family table clarifies which triggering relationships need compatible evidence.
3. Map fixed gate-current polarity to both line half-cycles
A controller that always sources gate current keeps one sign fixed while the main voltage alternates. In AN4363's positive-supply discussion, that combination requires the first and fourth quadrants across the two line polarities. A convenient control-supply arrangement therefore creates a specific two-polarity requirement, rather than establishing that every triac can be triggered in the intended manner.
The note's negative-supply discussion instead uses sinking gate current and identifies the second and third quadrants. This is a different control relationship even though the application still has both main-voltage polarities. The comparison must follow the gate-current reference through both halves, rather than assigning the whole circuit one positive or negative label.
These examples explain why the controller architecture and switch family should be considered together. A family with a different usable quadrant set cannot be accepted merely because another triggering field looks attractive. The useful selection question is whether the documented control relationship requires quadrants that the candidate actually supports. No connection diagram, gate resistor or trigger-timing setting is needed to preserve that functional distinction.
4. Recognize gate drives that follow the main-voltage polarity
AN4363 also discusses diac and opto-triac examples in which gate-current polarity follows main-voltage polarity. The note associates these examples with the first and third quadrants. This differs from a drive that keeps gate-current sign fixed across both main-voltage polarities, even if both arrangements are loosely described as AC switching.
The architectural distinction is how the two signs move together. A polarity-following arrangement uses one relationship when main voltage is positive and the corresponding relationship when it is negative. Its required pair should be compared with the named family's usable set, rather than copied from the fixed-source or fixed-sink examples. The shared presence of two half-cycles does not make those pairs identical.
Keep triggering architecture separate from what happens after triggering. The quadrant discussion does not establish holding behaviour, commutation capability or safe switching for an actual load. It supplies a narrower decision: which gate-current/main-voltage relationships the control architecture requires and whether the documented family supports them. That information improves the component requirement without becoming a mains-wiring instruction or a claim that an offered device is application-approved.
Sources and further reading
ST AN4363 Rev 3, physical pages 9–11: gate-current references, the explicitly read named-family quadrant table and control-architecture prose. No numeric trigger current, terminal map, mains wiring, holding or commutation result is supplied.