15 V Zener at 1 W — the clamping and regulation anchor
The 1N4744P/TR12 is a 15 V Zener diode rated for 1 W continuous power dissipation in the standard DO-204AL (DO-41) axial-lead package.
Operating envelope and leakage
Reverse leakage is specified at 5 µA maximum at 11.4 V — 76% of the nominal Zener voltage — so the diode draws negligible current before it breaks over. Maximum Zener impedance is 14 Ohms at the test current. A lower impedance means the Zener voltage shifts less when the load current varies, which is the difference between a clean clamp and a sloppy one in a transient suppressor circuit. Forward voltage is 1.2 V maximum at 200 mA — the diode can also serve as a general-purpose rectifier in a pinch, though the 1 W power limit governs the forward current capability.