6.4 V Zener, 500 mW — DO-35 axial
The 1N4582A-1 is a 6.4 V Zener diode in the DO-35 axial-lead package, rated for 500 mW maximum power dissipation. The ±5% tolerance on the Zener voltage means the regulation point sits between 6.08 V and 6.72 V at the specified test current — tight enough for most reference and clamping circuits in industrial control and instrumentation.
25 Ω impedance — what it means for regulation
Maximum Zener impedance (Zzt) is 25 Ω. This is the dynamic resistance at the nominal Zener current; a lower impedance means tighter voltage regulation under varying load current. For a 10 mA change in current through the diode, the voltage shifts by roughly 250 mV — acceptable for general-purpose clamping and simple shunt regulation, but not for precision references where a lower-impedance Zener or a bandgap device would be chosen.
The DO-35 axial package is through-hole mounted; leads are tin-plated copper. The 500 mW power derates linearly above 25°C ambient; at 175°C the allowable dissipation drops to zero, so the thermal path to the board (lead length, solder fillet, copper trace area) sets the real power limit.
Reverse leakage and test conditions
Reverse leakage is 2 µA maximum at 3 V reverse voltage — a low-leakage spec that keeps the diode from loading the circuit when it is not conducting. The 3 V test point is roughly half the Zener voltage, so the leakage measurement is taken well below the avalanche knee where leakage is dominated by surface effects rather than multiplication current.
The part is RoHS non-compliant (lead-bearing termination finish), which limits its use in EU RoHS-exempt applications but is common for military and high-reliability builds where tin whisker risk is a concern.