15 V regulation at 1 W — the DO-41 workhorse
The 1N4744PE3/TR8 is a 15 V zener diode rated for 1 W continuous power dissipation in the through-hole DO-204AL (DO-41) axial package. The ±10% tolerance on the nominal 15 V zener voltage (Vz) means the actual breakdown sits between 13.5 V and 16.5 V — wide enough that a design using it for a 15 V shunt regulator should pre-screen the bin if the downstream load expects tight regulation. The 14 Ohm maximum zener impedance (Zzt) at the test current governs how much the regulation voltage shifts under load current variation — a 10 mA change through the diode moves the zener voltage by roughly 140 mV, which is within the ±10% window but worth budgeting in a precision rail.
Reverse leakage and forward drop — the parasitic limits
Reverse leakage is specified at 5 µA maximum with 11.4 V applied across the junction — that is 76% of the nominal zener voltage, so the diode is already well into the knee region. In a high-impedance bias circuit, this leakage current can shift the operating point of the transistor or op-amp it is protecting. If the diode is used in a bidirectional clamp (back-to-back with another zener), the forward leg drops 1.2 V while the reverse leg regulates at 15 V, giving a total clamp of roughly 16.2 V.