1. PS2561BL-1-F3-Q-A Substitution Conclusion The PS2561BL-1-F3-Q-A is a highly viable alternative to the HCPL-817-30AE. The key differences are as follows: The PS2561BL offers a superior Current Transfer Ratio (CTR) range (100%-200% vs. 80%-160%), which provides greater output current margin and enhanced drive capability under the same input current. Its output withstand voltage is also slightly higher (80V vs. 70V), offering improved voltage headroom. However, its maximum forward current rating is marginally lower (40mA vs. 50mA), limiting the maximum permissible input current. Furthermore, its maximum collector-emitter saturation voltage (Vce(sat)) is higher (300mV vs. 200mV), which may result in slightly increased internal power dissipation and temperature rise when conducting higher currents. Given its package compatibility and comparable key specifications—including isolation voltage, output current, and fundamental switching speed (rise/fall times)—these differences are acceptable for most common applications (e.g., signal isolation, I/O interfacing). Therefore, the substitution feasibility is high.