1. PS2501A-1-A Substitution Conclusion Caution is advised when substituting the PS2501A-1-A for the original PS2501A-1-H-A, primarily due to differences in their Current Transfer Ratio (CTR) ranges. The PS2501A-1-A specifies a CTR of 50% (min) to 400% (max) at 5mA, whereas the original part is rated for 80% to 160%. The significantly lower minimum CTR of the substitute may result in a weakened output signal under low input current conditions, potentially compromising circuit reliability. Conversely, its higher maximum CTR could lead to output overdrive or increased noise. If the original design relies on a narrow CTR window—common in linear control or precision switching applications—direct substitution may be incompatible. Minor parameter variations, such as forward voltage (1.17V vs. 1.2V), are generally non-critical. Package and isolation voltage specifications are identical. Therefore, substitution feasibility hinges entirely on the application's CTR tolerance. It may be acceptable in non-critical or wide-tolerance circuits, but a thorough design review is recommended to mitigate performance risks.