The VOS617A-2T is a 1-channel phototransistor optocoupler from Vishay in a 4-SOIC surface-mount package. It provides 3750Vrms galvanic isolation between a DC input LED and a transistor output, with a current transfer ratio (CTR) specified between 63% and 125% at a 5 mA forward current. The 80V output rating and 50 mA output current capacity suit it for logic-level interfacing, PLC digital inputs, motor-drive feedback, and isolated DC-DC converter feedback loops where the secondary side needs to talk back to the primary controller without a direct ground path.
The 3750Vrms isolation rating is the key safety parameter. It qualifies the VOS617A-2T for reinforced insulation in mains-connected equipment per IEC 60950-1 and IEC 62368-1, as long as the working voltage stays within the creepage and clearance limits of the 4-SOIC package. For a 230 VAC line-powered supply, this part gives you the isolation margin to separate the primary-side controller from the secondary-side feedback without an extra isolation transformer winding. The 4-SOIC body width (4.40 mm) provides the creepage distance for basic insulation at 250 V working voltage; check your standard's requirement for reinforced insulation — some specs call for 8 mm or more, which this package alone doesn't deliver.
CTR spread: 63% to 125% at 5 mA — the design decision
The CTR min of 63% at 5 mA forward current sets the worst-case LED drive current you need to guarantee the output transistor saturates. With a 5 mA LED current, the output can sink at least 3.15 mA (63% of 5 mA). If your load resistor on the output side pulls 2 mA, you have margin. The 125% max means you don't have to over-drive the LED to cover the low end — a 5 mA forward current is enough for the full CTR range. The 3 µs rise/fall and 6 µs/4 µs turn-on/turn-off times limit this part to switching frequencies below about 50 kHz — fine for 50/60 Hz line sensing, relay drivers, and slow digital isolators, but not for high-speed comms like I²C or SPI isolation.
Temperature range and environment
The 110°C upper limit is 10°C above the typical 105°C industrial ceiling, giving a bit of headroom for self-heating in a confined enclosure. The -55°C low end covers cold-start conditions in outdoor gear. The transistor output type is standard phototransistor, not a photodiode-plus-amplifier, so the switching speed and CTR will drift with temperature — expect the CTR to increase by roughly 0.5% per °C above 25°C, which the 63% min at 25°C should still accommodate at 110°C.
Package and footprint
The 4-SOIC (also called 4-SSOP in the supplier device package field) is a 4-pin surface-mount package with a 4.40 mm body width and a 0.173" (4.40 mm) case height. The 4-SOIC footprint is shared with many Vishay and Broadcom optocouplers, so a board laid out for this part can often take a pin-compatible alternative without a layout change. The package is ROHS3 compliant per the listing.
Lifecycle and sourcing
It is ROHS3 compliant.