1. PS2561A-1-H-A Substitution Conclusion The PS2561A-1-H-A can serve as a substitute for the original PS2561A-1-V-A, provided key parameter compatibility is verified. The primary difference lies in the Current Transfer Ratio (CTR) range. The original V-A variant has a broad CTR range of 50%-400%, which exhibits significant inherent variation. In contrast, the substitute H-A variant offers a narrower, more tightly controlled CTR range of 80%-160%. The H-A version provides a more stable and predictable signal gain, enhancing design precision and consistency. However, this substitution sacrifices the design flexibility to exploit either very high CTR (>160%) or very low CTR (<80%) values that the V-A part could accommodate. All other critical specifications—including isolation voltage (5000Vrms), output configuration (transistor, 70V, 30mA), switching speed (3µs/5µs), and package (4-DIP)—are identical between the two models. Therefore, for most general-purpose signal isolation applications, the H-A version is a superior and more reliable direct replacement. Prior to substitution, it is essential to confirm that the original circuit design does not rely on the extreme CTR values offered by the V-A model.