Fast recovery diode for 400V bulk rail snubbing
The Microchip Technology 1N6621US/TR is a standard fast recovery diode rated for 2A average rectified current (Io) and 400V DC reverse voltage (Vr). Its 45ns reverse recovery time (trr) places it in the Fast Recovery category (≤500ns, >200mA), making it suited for snubbing, freewheeling, and clamp applications where switching losses in the diode dominate over conduction losses.
This sets the conduction loss at 3.2W peak — the SQ-MELF D-5A package must dissipate that through the board copper, not a heatsink. The 500nA reverse leakage at 400V is negligible at 25°C but doubles roughly every 10°C junction rise; at 150°C it climbs into the microamp range and adds to the thermal budget. Junction capacitance is 10pF at 10V, 1MHz. For a 400V rail snubber, the capacitance at the operating reverse voltage will be lower — the C-V curve typical for this class drops to ~2-3pF at 400V. This keeps the switching energy per cycle small enough for 100kHz+ hard-switched topologies.