Signal isolation for low-power AC/DC paths
The Panasonic AQY212EHAZ is a PhotoMOS™ AQY series solid-state relay that switches AC or DC loads up to 550 mA across a 0 V to 60 V range, with a 1.14 VDC input to trigger the internal LED. The SPST-NO (1 Form A) output gives you a normally-open contact that closes when the input is energised — no mechanical coil, no contact bounce, and no arc across the switching element.
On-resistance and thermal budget
The 2.5 Ohm max on-state resistance sets the conduction loss at 550 mA to roughly 0.76 W — well within the dissipation capability of the 4-SMD package when the copper traces on the PCB act as a heatsink. If your load current is lower, say 100 mA, the voltage drop across the relay is only 250 mV, which keeps the junction temperature rise negligible.
Package and board integration
The AQY212EHAZ comes in a 4-SMD package (0.300", 7.62 mm body width) with gull-wing leads. The 7.62 mm body width matches the common DIP-4 footprint, so it sits on the same PCB land pattern as a through-hole PhotoMOS relay — the gull-wing leads give you a lower profile and reflow-solder compatibility. No special bake-out required for MSL 1 parts, but verify the reel date code if it has been stored beyond the floor-life window.