1. HCPL-817-30AE Substitution Conclusion The HCPL-817-30AE is fully compatible with the original EL817(S)(TB) in key specifications such as package, isolation voltage, switching speed, and saturation voltage drop, providing a valid physical and basic electrical basis for substitution. Two critical differences exist: First, its current transfer ratio (CTR) range is significantly narrower (80%–160% vs. original 50%–600%), resulting in higher gain consistency but a substantially reduced dynamic range. If the original design relies on high CTR (e.g., >160%) for signal transmission or low-power drive, insufficient output or failure may occur. Second, its maximum output withstand voltage is increased to 70V (original: 35V), which is an enhanced feature, but the maximum forward input current is reduced to 50mA (original: 60mA), potentially limiting input-side drive capability. Substitution feasibility depends heavily on the actual operating point of the original application circuit: If the circuit operates within the 80%–160% CTR range and the input current is ≤50mA, direct substitution is possible with the benefit of higher output voltage tolerance; otherwise, circuit performance must be re-verified.