Military-grade 3.3 V zener in hermetic SQ-MELF
The 1N6485US/TR is a 3.3 V zener diode qualified to MIL-PRF-19500/406, rated for 1.5 W continuous power dissipation. The SQ-MELF A package is a hermetic, surface-mount ceramic body with metallized end caps — no plastic to outgas or crack in vacuum, high-altitude, or rapid thermal cycling. Operating junction temperature spans -65 to 175 °C, covering the full military temperature envelope. The ±5% tolerance on the nominal 3.3 V zener voltage is the standard tight bin for reference and clamping circuits. Maximum impedance (Zzt) is 10 Ohms at the test current — the dynamic resistance is low enough that the regulation line stays flat across the operating current range, which matters when the diode serves as a shunt regulator or voltage reference in an avionics supply rail.
Leakage and forward conduction — the fine print
Reverse leakage is 50 µA max at 1 V reverse bias — this is the off-state current that bleeds through the junction before breakdown. In a high-impedance bias network, 50 µA can shift the set point; design the divider current to dominate the leakage by at least 10:1. Forward voltage is 1.5 V max at 1 A — the diode can also serve as a high-temperature rectifier in the forward direction, but the 1.5 W total dissipation limits the duty cycle.