a19t stands for low-power triode electronic component.
The power triode is simply a triode used as a power switch.
Simply put, it is a triode as a power switch. The structure is a three-terminal (base, collector, emitter) semiconductor component composed of a vertical four-layer NPN structure. The working characteristics are divided into cut-off zone, saturation zone and amplification zone. In the field of power electronics, the NPN type is mainly used, and the drive mode is current drive, that is, the base current must be continuous in order to maintain the on-state of the device.