1. PS2561A-1-H-A Substitution Conclusion After a detailed comparison, the PS2561A-1-H-A can be fully compatible with and directly replace the original PS2561A-1-A. Both models are identical in all key electrical and mechanical specifications, including isolation voltage (5000Vrms), package (4-DIP), maximum output current (30mA), and switching speed. This ensures direct physical and basic functional compatibility. The only difference lies in the Current Transfer Ratio (CTR) range: the original model has a wide CTR range of 50% to 400%, while the H-A version features a tightened range of 80% to 160%. The H-A model is essentially a "binned" or "high-consistency" version of the original part, where the gain (CTR) is strictly screened to a more focused and stable interval. This difference does not invalidate the substitution. On the contrary, using the H-A variant can provide higher consistency and reliability by reducing potential circuit performance variations—such as in drive capability and response uniformity—caused by excessive CTR dispersion among devices. For most applications, it is the preferred choice. The substitution is entirely feasible from both a technical and physical standpoint.