600 V off-state, 1 A RMS — what this TRIAC handles
The Z0103MN 5AA4 is a logic-level sensitive-gate TRIAC from ST, rated for 600 V off-state voltage and 1 A RMS on-state current. The 7 mA holding current keeps the TRIAC latched on through the zero-cross of a typical 50/60 Hz mains cycle, so it stays conducting until the load current drops below that threshold.
SOT-223 — small footprint, reflow assembly
Housed in a SOT-223 surface-mount package (TO-261-4 variant), this part fits on compact PCBs where through-hole TRIACs would consume too much board area. The tab is the main terminal (MT2) and carries the load current — the PCB copper pad under the tab should be sized for thermal dissipation at 1 A RMS.