AC/DC input detection without an external bridge
The H11AA1M accepts both AC and DC input drive, which means a single optoisolator can sense 50/60 Hz mains voltage or a DC logic signal without adding a diode bridge on the primary side. The internal back-to-back LEDs handle the AC polarity reversal — the phototransistor turns on across both half-cycles, giving you a full-wave detection pulse that a microcontroller timer can measure for zero-crossing or frequency counting. Isolation is rated at 4170Vrms, a common figure for reinforced insulation in 240VAC line-monitoring circuits. The 6-DIP (0.300-inch, 7.62mm) through-hole package keeps creepage distance above 8 mm, which simplifies PCB layout for safety-agency clearance requirements.
Transistor output with base access for speed trade-offs
Unlike many optoisolators that only expose the collector and emitter, the H11AA1M brings out the phototransistor base. This lets you add a resistor between base and emitter to speed up turn-off at the cost of reduced current-transfer ratio — useful when the downstream logic expects a clean edge at line-frequency transitions. The minimum CTR is 20% at 10 mA forward current, so with a 10 mA AC input the output can sink 2 mA into a 5V pull-up while staying below the 400mV Vce(sat) ceiling. Maximum output voltage is 30V and continuous output current per channel is 50 mA. These ratings suit 5V or 12V logic rails, but the 30V ceiling also covers 24V PLC input modules — the phototransistor can drive a 24V pull-up through a current-limiting resistor without exceeding the breakdown.
Active production — no immediate EOL risk
The base product number H11AA covers multiple CTR and package variants, so if future design changes require a different CTR bin, the footprint and pinout stay the same. The through-hole 6-DIP is a mature, widely second-sourced package; no fine-pitch reflow concerns.