5300Vrms isolation — where this optocoupler fits
The Vishay SFH640-2 is a single-channel phototransistor optocoupler with a base connection, packaged in a 6-DIP through-hole housing (0.300" pin spacing). Its 5300Vrms isolation rating puts it in the class used for reinforced insulation in motor drives, industrial PSU feedback loops, and PLC digital input modules — anywhere you need to pass a DC-level signal across a safety barrier without galvanic coupling.
The current transfer ratio is specified at 63% minimum to 125% maximum, both measured at 10 mA forward current. That 2:1 spread is tight enough that you can pick a single load resistor value and still guarantee the output saturates across temperature and device-to-device variation — no need to bin or overdrive the LED. The transistor-with-base output (pin 6) lets you pull the base low to force the output off faster, or add a speed-up capacitor between base and collector to shave the 5.5 µs fall time.
300V output — not just a logic-level switch
Rated Vce(max) of 300V means the output transistor can switch 48V or 120V DC rails directly, not just 5V or 24V logic. The 50 mA per-channel current limit is modest — enough to drive a small relay coil or a gate resistor on a downstream MOSFET, but not a contactor. If you need more current, the base-drive access lets you add an external transistor stage without a second optocoupler.
Temperature range and package reality
Rated from -55°C to 100°C operating, so it lives in outdoor telecom cabinets, engine-bay electronics, and unheated factory floors without derating. The 6-DIP through-hole package is a standard 7.62 mm pitch — no special footprint, easy to hand-assemble or wave-solder. The base connection is the sixth pin; if you are replacing a 4-pin optocoupler, the extra pin needs a pad or a no-connect.
Lifecycle and sourcing posture
It is ROHS3 compliant.