What the 4170Vrms isolation means for your circuit
The H11A1M is a 1-channel optoisolator from onsemi that provides 4170Vrms galvanic isolation between a DC input LED and a phototransistor output with a base connection. This isolation rating is typical for industrial signal isolation — it separates a 24V PLC input from a 5V logic side, or breaks a ground loop between two pieces of equipment that share a common-mode voltage difference. The base pin on the output side gives you the option to bias the transistor for faster switching or to use it in a Darlington pair for higher gain — a feature missing from simpler three-pin optocouplers. With a minimum current transfer ratio of 50% at 10mA forward current, it guarantees the output can sink enough current to drive a TTL or CMOS input when the LED is on.
Switching speed and drive margin
Typical turn-on and turn-off times are both 2µs, which means the H11A1M can handle signal frequencies up to about 250 kHz before the output waveform starts to round off. For a 24V PLC input scanning at 1 kHz, this is plenty of margin — the 2µs delay is invisible to the controller. The output transistor saturates at 400mV max with the base pin open, so the logic-side pull-up resistor sees a clean low level. Maximum output voltage is 30V, which covers 5V, 12V, and 24V logic rails. The LED side can take up to 60mA forward current, but the 10mA test condition for the CTR spec is the sweet spot for most designs — running it at 20mA gives you headroom for LED aging.
Package and board-fit for hand-soldering
The 6-DIP package with 0.300-inch (7.62mm) row spacing and 2.54mm pin pitch is a through-hole part that fits standard perfboard and breadboards. The 6-PDIP supplier device package is the same footprint — any 6-pin DIP socket or solder pad layout works. The tube packaging means you get a batch of parts aligned in a plastic tube, which is fine for bench work but not reel-fed pick-and-place. The through-hole body is easy to hand-solder or rework with a standard iron — no hot-air station needed.
Obsolete — what that means for sourcing
onsemi has marked the H11A1M as obsolete. This means the manufacturer no longer produces it, and there is no direct drop-in replacement from onsemi with the same pinout and base connection.