5000Vrms isolation in a 4-DIP through-hole package
The FOD817A is a single-channel DC-input transistor-output optocoupler from onsemi in a 4-DIP (0.300", 7.62mm) through-hole package. Its 5000Vrms isolation voltage suits primary-to-secondary feedback in switch-mode power supplies, motor-drive interface circuits, and industrial PLC digital inputs where galvanic separation is mandatory. The 80%–160% current transfer ratio (CTR) at 5 mA forward current gives predictable LED drive margin — the 80% minimum guarantees the output transistor saturates with standard 5V logic inputs, even with LED ageing or temperature drift.
Parametric deep-dive: speed, output, and temperature
Rise and fall times are 4 µs and 3 µs typical — fast enough for 100 kHz switching supplies or low-speed serial isolation, but not for high-speed data links. The 70V output rating and 50 mA continuous output current handle relay drivers, gate-drive buffers, and logic-level translation up to 48 V rails. This suits outdoor telecom enclosures, under-hood automotive-adjacent electronics, and industrial motor drives where ambient heat exceeds 85°C. Maximum Vce saturation is 200 mV at rated current — low enough to keep dissipation under 10 mW per channel in most logic-level shift applications.
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