Active optoisolator with AC/DC input flexibility
The onsemi FOD814S is an active-production, 1-channel optoisolator that accepts both AC and DC input, making it suitable for line-voltage zero-crossing detection or DC logic isolation in a single BOM line. Rated for 5000Vrms isolation, it provides reinforced galvanic separation between the primary and secondary circuits, which is the deciding parameter for meeting IEC 60950-1 or IEC 62368-1 clearance in an isolated power supply or PLC input module.
Current-transfer ratio and switching performance
The current-transfer ratio (CTR) spans 20% minimum to 300% maximum at a forward current of 1 mA, which defines the LED drive budget: a 1 mA input can saturate the output transistor, but at the low end of the CTR range a higher input current or a pull-up resistor adjustment is needed to guarantee the logic level at the receiver. Typical rise and fall times of 4 µs and 3 µs respectively set the practical switching ceiling — for a 10 kHz PWM or a 115.2 kbps serial isolator the output slew will track the input, but above 50 kHz the propagation skew between channels becomes a timing-closure risk.
Package and thermal operating envelope
The operating temperature range of -55°C to 105°C covers industrial and some military/aerospace ambient conditions; the 105°C upper limit is the junction temperature boundary — above this the CTR degrades and the isolation lifetime shortens per the Arrhenius model in the onsemi reliability report. Supplied in tube packaging, the part is compatible with tube-fed pick-and-place machines; for reel-fed lines a tape-and-reel variant may be preferred, but the tube format is standard for prototype and low-volume builds.