1. Rated Current and Forward Voltage: The MBRF2545CTG has a significantly higher rated current (12.5A) than the MBRF1545CT-E3/45 (7.5A). However, its maximum forward voltage drop at rated current is also higher (700mV vs. 570mV). At the same actual operating current (e.g., 7.5A), the replacement part will exhibit greater conduction loss (Pcond = Vf × If), potentially resulting in elevated junction temperature and reduced efficiency. 2. Reverse Leakage Current: The reverse leakage current of the MBRF2545CTG (200µA) is double that of the MBRF1545CT-E3/45 (100µA). This indicates that under high-temperature and high-reverse-voltage conditions, the substitute will have higher static power dissipation and thermal load, adversely affecting system stability in high-temperature environments or low-power designs. 3. Maximum Junction Temperature and Product Series: The MBRF2545CTG features a higher maximum junction temperature of 175°C (compared to 150°C) and belongs to onsemi's SWITCHMODE™ series. This suggests it is optimized for high-frequency switching power supply applications, offering better surge resilience and high-temperature operation capability. In contrast, the MBRF1545CT-E3/45 is a general-purpose series part. 4. Package Isolation: The MBRF1545CT-E3/45 is explicitly marked as having an "Isolated Tab," while the MBRF2545CTG does not emphasize this feature. If the original design relies on electrical isolation between the TO-220 package and the heatsink, it is essential to verify whether the MBRF2545CTG provides an equivalent level of isolation before substitution. Failure to do so may introduce a short-circuit risk.