4.3 V Zener in a hermetic SQ-MELF
The 1N6315US/TR is a 4.3 V Zener diode from Microchip Technology rated for 500 mW continuous power dissipation in the SQ-MELF B package. The ±5% tolerance on the nominal Zener voltage means the regulation point falls between 4.085 V and 4.515 V at the specified test current — tight enough for most reference and clamping applications in analog and mixed-signal circuits. The SQ-MELF (Surface Mount Metal Electrode Leadless Face) package is a hermetic ceramic body with metallized end caps — no plastic molding, no moisture absorption path. This construction suits high-reliability environments where outgassing or moisture ingress disqualifies standard SOT-23 or SOD-123 packages.
Temperature range and thermal margin
Operating junction temperature spans -65°C to 175°C — the full military temperature band. A 500 mW part in SQ-MELF dissipates heat through the end-cap solder joints and the board copper; at 175°C junction the derated power is near zero, so the actual allowable dissipation depends on the board's thermal resistance and the ambient temperature. Reverse leakage is specified at 2 µA maximum at 1 V reverse voltage — well below the Zener knee, confirming the diode is fully off before breakdown. Forward voltage is 1.4 V maximum at 1 A forward current, typical for a silicon junction this size.