What the 500 mA rating means for your BOM
The AQY212SX is a PhotoMOS™ solid-state relay from Panasonic's AQY series, switching AC or DC loads up to 500 mA at 0–60 V. The 2.5 Ohm on-state resistance sets the conduction loss: at full load, dissipation is roughly 0.625 W, which the 4-SOP package must sink through the board copper — no heatsink, so the ambient temperature and trace geometry govern the derating. The SPST-NO (1 Form A) circuit closes when the input LED sees 1.14 VDC typical. This is a dry-contact replacement for electromechanical relays in low-level signal switching — no contact bounce, no arc, and the output can pass both polarities.
Housed in a 4-SOP package with a 4.40 mm body width and gull-wing leads, the AQY212SX sits on a standard SOIC-4 footprint. The surface-mount profile suits pick-and-place assembly; the gull-wing form gives visible solder joints for inspection. The base product number AQY212 covers the family; the SX suffix denotes the specific package and packaging variant.