What the 120 mA / 350 V rating means on the bench
The AQY210KS is an SPST-NO (1 Form A) solid-state relay rated for 120 mA continuous load current and a load voltage range of 0 V to 350 V AC or DC. That 350 V ceiling covers 240 VAC line switching with margin, while the 120 mA current handles signal-level loads like PLC inputs, sensor outputs, or small solenoid valves. The 35 Ohm on-state resistance (max) means the voltage drop across the relay at 120 mA is about 4.2 V — acceptable for many signal circuits but worth checking if the downstream load requires a tight voltage rail.
4-SOP surface-mount — board-fit checklist
The 4-SOP is the same package used across the PhotoMOS AQY series, so a single PCB layout serves multiple current/voltage variants. Supplied in tube packaging — not tape-and-reel — so it is suited for prototype runs, low-volume production, or bench repair where a pick-and-place feeder is not needed.