Darlington optoisolator for high-gain switching
The FOD852SD is a single-channel DC-input Darlington optoisolator from onsemi that delivers 5000Vrms isolation in a compact 4-SMD gull-wing package. Its Darlington output stage gives a current transfer ratio ranging from 1000% to 15000% at 1mA forward current — meaning a 1mA LED drive can switch up to 150mA on the output side. This part is typically specified where a microcontroller or logic-level signal needs to drive a higher-current load — relays, contactors, solenoids, or small motors — while maintaining galvanic isolation between the control and power domains.
Output ratings and switching speed
The output can handle up to 300V collector-emitter voltage and 150mA continuous current, with a Vce saturation of 1.2V max. Rise time is 100µs typical, fall time 20µs — fast enough for 50/60 Hz AC switching or DC load control, but not intended for high-frequency PWM. Compared to transistor-output siblings like the FOD814A3SD (200mV Vce sat, 4µs rise/fall), the Darlington trades switching speed for much higher gain. If your load needs less than 50mA and you want faster edges, a transistor-output part may be a better fit.
Housed in a 4-SMD gull-wing package (supplier device package 4-SMD), it's a surface-mount part suited for reflow assembly. The operating temperature range is -30°C to 100°C, which covers most industrial and commercial environments but not extended automotive or military grades. The part is ROHS3 compliant.