Zener voltage and power rating
The 1N4729AUR is a 3.6 V Zener diode in a DO-213AB MELF package, rated for 1 W continuous power dissipation. Maximum impedance (Zzt) is 10 Ohms at the Zener test current, so the regulation slope is moderate — the output voltage shifts about 10 mV per mA of load change. For a simple shunt regulator feeding a low-power microcontroller or a comparator reference, this is workable; for a precision ADC reference, a lower-impedance Zener or a bandgap device would be tighter. Reverse leakage is specified at 100 µA maximum at 1 V reverse bias, which is well below the Zener knee — the diode stays high-impedance until the breakdown region. Forward voltage is 1.2 V max at 200 mA, typical for a silicon junction at this current density.
Package and temperature range
The DO-213AB MELF (metal electrode leadless face) package is a cylindrical, end-capped surface-mount body. It places flat on the pad with no lead coplanarity issues — the solder wets the full end-cap circumference. The package footprint is standard; the MELF's round profile can tombstone during reflow if the pad geometry is asymmetric, so keep the pad lengths equal on both ends. The 175°C junction limit is the same as many power diodes — derate power above 25°C per the thermal resistance curve (not in this listing, but standard for the package).
Active production and sourcing
Microchip Technology lists the 1N4729AUR as Active.