12 V zener with a 175°C junction ceiling
The HZ12HB2-E is a 12 V nominal zener diode from the HZ(H) series, rated for 500 mW maximum power dissipation in a DO-35 axial-lead package. The ±2.08% tolerance on the zener voltage is tighter than the common 5% grade, which matters when the diode is used as a shunt reference or a clamp threshold where the guard band is tight. The 175°C junction temperature rating (TJ) allows this part to sit in hot environments — engine compartments, industrial ovens, or near power resistors — where a standard 150°C rated zener would drift or fail. The reverse leakage is specified at 1 µA maximum at 9.5 V, giving a clean knee below the 12 V clamp point.
DO-35 axial — what the package tells the board
Through-hole DO-35 (DO-204AH) body, axial leads. The part stands off the board on its lead bends, so the body is not in contact with the PCB — that air gap helps thermal performance but means the lead length between the solder joint and the glass body sets the vibration fatigue life. Keep the lead bend radius generous and the stand-off height consistent across the BOM. The 35 Ohm maximum zener impedance (Zzt) at the test current means the regulation slope is moderate — expect the voltage to shift a few hundred millivolts as the current varies. For a precision reference, a lower-impedance zener or a shunt reference IC would be a tighter fit; for a clamp or a simple regulator tail, this is fine.
Listed as current production with an active lifecycle status. The HZ(H) series is a mature line, so the risk of a sudden EOL is low, but the DO-35 package is gradually being displaced by SMD equivalents in high-volume designs — if the board is through-hole for a reason (vibration, rework, legacy BOM), this part stays available through the independent channel.