Active production, Darlington output, 4170 Vrms barrier
The MOC8021M is an onsemi single-channel optoisolator with a Darlington phototransistor output, rated for 4170 Vrms isolation and a minimum current transfer ratio of 1000% at 10 mA forward current.
CTR floor and output drive — what the 1000% min means
With a minimum CTR of 1000% at If=10 mA, the Darlington output can deliver up to 150 mA continuous while the input LED draws only 10 mA. This high gain reduces the LED drive current requirement, which matters when the input-side supply is current-limited or shared across multiple channels. The typical turn-on time is 8.5 µs and turn-off is 95 µs — fast enough for 50/60 Hz line-frequency switching and low-speed PLC inputs, but not for high-speed data or PWM above a few kHz.
Package and temperature grade — through-hole, industrial range
Housed in a 6-DIP (0.300-inch, 7.62 mm pitch) through-hole package, the MOC8021M suits boards where wave-solder or hand-solder assembly is preferred over reflow. The operating temperature range of -40°C to 100°C covers industrial and appliance environments, including outdoor telecom cabinets and factory-floor controls. The DC input type means the LED is polarity-sensitive — a series resistor sets the forward current, and the 1.18 V typical forward drop should be factored into the resistor calculation.