1. Switching Speed & Reverse Recovery Time (trr): This is the fundamental distinction. The MR851RLG is a fast recovery diode (trr=300ns), whereas the 1N5401-G is a standard recovery diode (trr >500ns). When the diode transitions from the conducting state to blocking reverse voltage, the MR851RLG recovers its charge significantly faster. In circuits such as switching power supplies, freewheeling, and high-frequency rectification, the excessively long reverse recovery time of a standard recovery diode leads to substantial switching losses, increased device heating, and can generate significant voltage spikes and electromagnetic interference (EMI). In severe cases, this can result in poor circuit efficiency or device damage. 2. Forward Voltage Drop (Vf @ 3A): The Vf of the 1N5401-G (0.95V) is notably lower than that of the MR851RLG (1.25V). At the same forward current, the 1N5401-G exhibits lower conduction loss and reduced heat generation. This is a common advantage of standard recovery diodes in low-frequency applications. However, in high-frequency applications, its switching losses (determined by point 1 above) will far outweigh the benefit gained from lower conduction loss. 3. Manufacturer & Brand: The MR851RLG is sourced from onsemi (a tier-1 mainstream supplier), while the 1N5401-G comes from Comchip Technology (generally regarded as a tier-2 or alternative supplier). Tier-1 suppliers typically offer greater credibility and documented validation data regarding reliability, parameter consistency, long-term supply stability, and performance guarantees under extreme conditions. For applications with high-reliability requirements (e.g., industrial, automotive), the brand is a factor that must be considered.