5.1 V regulation at 2 W — the thermal budget and the load
The SMAJ4733CE3/TR13 is a 5.1 V Zener diode in a DO-214AC (SMA) surface-mount package, rated for 2 W continuous power dissipation. That 2 W ceiling sets the practical current limit: at 5.1 V, the diode can sink roughly 392 mA before the junction hits its thermal limit at 150 °C ambient — but the actual derating depends on the PCB copper area under the cathode tab, which is the primary heat path in the SMA package. The ±2% tolerance on the nominal 5.1 V means the actual Zener voltage falls between 4.998 V and 5.202 V across the operating temperature range of -55 °C to 150 °C. For a 5 V rail clamp or a reference shunt, that band is tight enough to keep the load within spec without a separate trim resistor.
Impedance and leakage — what the bench sees
Maximum Zener impedance (Zzt) is 7 Ohms at the test current. That figure governs how much the Zener voltage shifts when the load current varies: a 10 mA change in current through the diode shifts the voltage by 70 mV worst-case. For a simple shunt regulator feeding a low-power MCU or a comparator reference, that ripple is usually acceptable — but it matters if the load steps hard. Reverse leakage is 10 µA max at 1 V reverse bias. In a battery-powered circuit that idles at 1 µA system draw, that 10 µA leak from the Zener alone dominates the sleep budget — you would need a series switch or a higher-voltage Zener to keep the quiescent current down. Forward voltage drop is 1.2 V max at 200 mA forward current. If the diode is used in a bidirectional clamp (back-to-back Zeners), the forward drop adds to the clamp threshold on one polarity.
Active production — no lifecycle risk for new builds
The base product number is SMAJ473, which covers the whole family of 2 W Zener diodes in the DO-214AC package. The CE3 suffix indicates the ±2% tolerance grade and the /TR13 suffix denotes Tape & Reel packaging for automated pick-and-place assembly.