**Key Features**:
1. Available as unidirectional SCR and TRIAC (bidirectional), ideal for AC contactless switching.
2. Main parameters: average on-state current IT, forward/reverse blocking voltage, gate trigger voltage VGT, holding current IH.
3. Packages include TO-92, TO-220, SOT-23, etc.
4. Widely used in motor speed control, power regulation, dimming, voltage regulation, and servo systems.