Isolation and signal transfer for a 5000Vrms barrier
The FOD2741BT is a single-channel optocoupler from onsemi with a DC input and a phototransistor output. The current transfer ratio (CTR) is specified at 100% minimum and 200% maximum, both measured at a forward current of 10 mA. That spread tells you the output transistor will sink at least as much collector current as the LED draws — useful when you are budgeting the pull-up resistor on the secondary side without overdriving the downstream logic input.
Temperature range and output drive capability
The output transistor can sink up to 50 mA continuously and saturates at 400 mV max — low enough to drive a 5 V logic input directly without a second buffer stage. Maximum output voltage is 30 V, so the collector can be pulled up to a 24 V industrial bus or a 12 V auxiliary rail. The 1.5 V forward voltage on the LED side is typical for a GaAs infrared emitter at rated current.
Housed in an 8-pin DIP with 0.400-inch (10.16 mm) body width — the wider DIP footprint common on optocouplers that need the creepage distance for high-voltage isolation. The supplier device package is listed as 8-MDIP, which is onsemi's moulded DIP variant with standard 2.54 mm pin pitch. Through-hole mounting suits prototype boards and production runs where wave solder is the primary assembly method. Supplied in tube packaging, so the pins are protected during handling and the tubes feed directly into auto-insertion equipment that handles DIP outlines.
onsemi has marked the FOD2741BT as obsolete. For existing BOM lines that require this exact part number, the supply path runs through independent distribution — surplus inventory that was originally manufactured by onsemi and has been sitting in bonded stock since the last production run. Because there is no pin-compatible drop-in from onsemi's current catalogue, a buyer replacing this part in a new design would need to evaluate a functionally equivalent optocoupler with the same 8-DIP footprint, 5000Vrms isolation, and similar CTR window.