4.3 V Zener — regulation and clamping in extreme thermal environments
The 1N6488 is a 4.3 V Zener diode rated for 1.5 W continuous power dissipation in the DO-204AL (DO-41) axial-lead package. The ±5% tolerance on the nominal voltage means the actual breakdown sits between 4.085 V and 4.515 V at the specified test current — tight enough for a basic shunt regulator or input-clamp rail but not a precision band-gap reference. Its 9 Ohms maximum Zener impedance (Zzt) at the operating point means the regulation voltage shifts about 9 mV per mA of load current change. For a 10 mA shunt current, the output moves less than 90 mV — acceptable for a 5 V logic supply clamp or an over-voltage crowbar trigger. At 175°C junction, the 1.5 W rating must be derated per the thermal resistance of the lead length and board copper — a free-air axial lead in still air dissipates roughly 1 W before the junction hits 175°C at 25°C ambient.
Reverse leakage and forward drop — signal-chain boundaries
Reverse leakage is 5 µA maximum at 1 V reverse bias — well below the 1 V knee, so a 4.3 V rail clamped by this diode sees under 5 µA of leakage until the rail approaches 4.3 V. Forward voltage is 1.5 V maximum at 1 A forward current, characteristic of a silicon Zener operating as a rectifier in the forward quadrant.