Isolation and signal transfer in a 4-SOP package
The VOM617A-3T is a single-channel transistor-output optocoupler from Vishay, built for galvanic isolation between a DC input and a transistor output. Its 3750Vrms isolation rating covers basic functional isolation in mains-powered equipment — think PSU feedback loops, digital input modules on a 24V PLC bus, or driving a low-side switch from a controller that shares a ground with a noisy motor drive. The 4-SOP (small-outline package with gull-wing leads) footprint matches the standard SOIC-4 land pattern, so it drops onto a board without a special pad layout. The package is surface-mount, and it ships on tape-and-reel for automated assembly or cut-tape for prototype runs.
What the CTR range means for your circuit margin
Current transfer ratio is the headline spec that decides whether the opto works in your circuit. The VOM617A-3T guarantees a CTR of 100% to 200% at a forward current of 5 mA. That means at 5 mA in, the output transistor can sink at least 5 mA and at most 10 mA — a tight bin that gives the designer a predictable min-max window for the pull-up resistor and the downstream logic threshold. A wider CTR bin (like the 50-600% on a generic 4N35) forces you to over-design the collector load to handle the gain spread; this part's 2:1 ratio keeps the resistor value in a tighter band. The output transistor is rated for 80 V collector-emitter and 50 mA continuous current.
Temperature range and switching speed
Rated for -55°C to +110°C operating ambient, this opto covers industrial and commercial environments without a temperature grade downgrade. The 3 µs typical rise and fall times and 6 µs / 4 µs turn-on / turn-off times place it in the medium-speed class — fine for 10-50 kHz switching or status feedback, but not for high-speed isolated data links. Forward voltage is 1.1 V typical at rated current, with an absolute maximum forward current of 60 mA. The input is a simple LED — no logic-level threshold, so the series resistor sets the If and therefore the CTR operating point. Design the resistor for 5 mA forward current to land in the middle of the CTR spec window.