1. Isolation Voltage: The H11B1 is rated for 5300 Vrms, while the H11B1M is rated for 4170 Vrms. In applications involving high potential differences or high‑noise environments (such as industrial power supplies or motor drives), the H11B1 offers greater insulation margin and higher safety. Substitution is only acceptable if the actual working voltage remains below 4000 Vrms. 2. Output Current and Voltage: The H11B1M has a nominal output current of 150 mA and a withstand voltage of 30 V, whereas the H11B1 does not specify a nominal output current and is rated for 25 V withstand voltage. This suggests the H11B1M may be optimized for higher load capability, but it must be confirmed that the H11B1 is not operated beyond these parameters in the actual application. 3. Input Current Limit: The H11B1 has a maximum DC forward current of 100 mA, compared to 80 mA for the H11B1M. If the original design uses a higher drive current (e.g., >80 mA), direct replacement could risk overcurrent on the input‑side LED. 4. Operating Temperature Range: The H11B1 supports operation down to –55 °C, while the H11B1M is limited to –40 °C. In low‑temperature environments (such as aerospace or outdoor equipment), the H11B1M may fail to meet extreme temperature requirements.