5000Vrms isolation in a 4-SMD gull-wing package
The FOD817C3SD is a single-channel phototransistor optoisolator from onsemi's FOD817 family. Its 5000Vrms isolation rating qualifies it for reinforced insulation in mains-referenced circuits — think offline power supplies, motor-drive feedback, and PLC digital inputs where the primary side runs at line voltage and the secondary side must stay galvanically separated. The DC input side drives an IR LED; the output is a phototransistor rated for 70 V collector-emitter and 50 mA continuous current. The 4-SMD gull-wing package sits flat on the board — the 0.4-inch lead span is a standard footprint shared with DIP-4 through-hole parts, so the layout swaps between the two without a board respin.
CTR bin C – 200% to 400% at 5 mA forward current
The 'C' in the order code marks the current-transfer-ratio bin: minimum 200%, maximum 400% at If = 5 mA. That 2:1 spread means the designer sizes the collector load resistor for the worst-case minimum CTR — at 200% the output transistor sinks 10 mA from a 5 mA input, which is still enough to drive a logic gate or a 5 V relay coil through a 500 Ω pull-up. The 4 µs rise / 3 µs fall times keep the switching clean up to about 50 kHz, adequate for isolated serial interfaces and low-speed PWM. Compared to the sibling FOD817ASD (CTR 80–160%) and FOD817B3SD (CTR 130–260%), the C bin gives the highest minimum gain — useful when the input drive current is limited or when the output must drive a heavier load without an external transistor. The D bin (300–600%) offers more headroom but the extra gain is rarely needed unless the LED current is below 2 mA.
Active lifecycle and sourcing position
We source the FOD817C3SD against your BOM quantity and target lead-time. No minimum order threshold beyond the reel increment.