5000Vrms isolation in a 4-DIP through-hole package
The onsemi FOD817A300 is a single-channel transistor-output optocoupler in the standard 4-DIP (0.300", 7.62mm) through-hole package. It provides 5000Vrms galvanic isolation between a DC input LED and a phototransistor output, making it a fit for isolating low-voltage control logic from higher-voltage power circuits or for breaking ground loops in industrial sensor interfaces.
CTR range and switching speed define the drive margin
Current transfer ratio (CTR) is specified at 80% minimum and 160% maximum when the LED is driven at 5mA. This band tells the designer how much output current the phototransistor can sink relative to the input drive — a 5mA LED current guarantees at least 4mA of output drive capability at the collector, which is sufficient to pull a standard TTL or CMOS logic input low through a pull-up resistor. The 4µs rise and 3µs fall times (typical) set the practical switching ceiling around 100 kHz for a resistive load; above that, the output waveform rounds off and the downstream logic may miss edges.
Output ratings and temperature range
The phototransistor is rated for 70V collector-emitter voltage and 50mA continuous output current, with a saturation voltage of 200mV maximum at the rated current.