43 V regulation at ±1% — what the tolerance buys you
The 1N6015D: The 43 V nominal zener voltage with a ±1% tolerance holds the regulation point between roughly 42.57 V and 43.43 V across temperature and lot — tight enough for a precision shunt reference or a voltage clamp where the threshold must stay within a few hundred millivolts. Maximum zener impedance is 150 Ohms at the test current — the dynamic resistance shifts the output voltage slightly with load current, so for the tightest regulation the bias current should stay near the test point specified in the full datasheet.
500 mW in a DO-35 — thermal budget for the board
Rated at 500 mW maximum power dissipation in the DO-204AH / DO-35 axial-lead package. At 43 V that works out to about 11.6 mA continuous — above that current the junction temperature climbs past the derating limit unless the leads are heat-sunk to the board copper. The junction handles extreme thermal cycling without parametric drift, which matters for avionics, downhole tools, or engine-bay electronics where the ambient sees both deep cold and sustained heat.
Reverse leakage and forward drop — the real-world limits
Maximum reverse leakage is 100 nA at 33 V reverse voltage — for a 43 V zener this means the shunt current drawn before breakdown is negligible, so it won't load a high-impedance bias node or discharge a timing capacitor prematurely. Forward voltage is 1.1 V maximum at 200 mA forward current — the diode conducts as a standard signal diode in the forward quadrant, useful if the same part doubles as a protection clamp in both polarities.