225 V reverse blocking, 500 mA forward — the DC rail guard
The 1N6661/TR is a standard recovery diode rated for 225 V DC reverse voltage and 500 mA average rectified current, packaged in a DO-35 axial leaded form. It belongs to Microchip's MIL-PRF-19500/587 qualified series, meaning each device lot is screened to the military specification for hermeticity, temperature cycling, and electrical parameter limits. With a standard recovery speed exceeding 500 ns at 200 mA forward current, this diode is intended for 50/60 Hz line rectification, DC bus polarity protection, and freewheeling clamp applications where switching speed is not the primary constraint. The 225 V reverse voltage covers 120 VAC and 240 VAC rectified rails with margin.
Junction temperature range and leakage floor
The operating junction temperature spans -65°C to 175°C, a full military-grade range that suits avionics, satellite, and downhole equipment where ambient extremes exceed commercial limits. Reverse leakage is specified at 50 nA maximum at 225 V reverse bias — this low leakage floor is critical for hold-up capacitor circuits and high-impedance bias networks where every nanoamp affects the droop rate. Forward voltage is 1 V maximum at 400 mA forward current. At the full 500 mA average rating, the forward drop will be slightly higher, but the 1 V figure at 400 mA gives a reasonable estimate for power dissipation in continuous duty: roughly 0.5 W at full load, which the DO-35 glass body can handle with adequate lead-length heat sinking.
The tape-and-reel packaging (TR suffix) is the standard production reel format for automated insertion equipment.