150 V Zener with ±1% tolerance — precision regulation in a DO-35 glass package
The 1N6028D is a 150 V Zener diode from Microchip Technology, specified with a ±1% tolerance that holds the regulation voltage tighter than the standard 5% or 10% grades — useful when the Zener serves as a voltage reference or clamps a supply rail that cannot drift more than a few volts. The 500 mW power dissipation rating sets the steady-state current ceiling: at 150 V, the maximum continuous current is roughly 3.3 mA, so the bias resistor must be sized to keep the diode below that limit across the input voltage range. The DO-35 glass axial-lead package (DO-204AH) is a through-hole format that mounts into standard 0.100-inch pitch holes on a PCB or terminal strip. The glass body handles the full -65°C to 175°C operating range without cracking — that military-grade temperature span covers engine-bay electronics, downhole tools, and avionics bay environments where commercial parts would fail the cold soak or the hot bench test.
Impedance and leakage — what limits the regulation quality
The maximum Zener impedance (Zzt) is 1.25 kOhms at the test current. This impedance is the dynamic resistance at the Zener knee — a lower value means the voltage stays flatter as the current varies. At 1.25 kOhms, the 150 V output will shift about 1.25 V for every 1 mA of load current change, which is acceptable for a clamp or a coarse reference but not for a precision band-gap substitute. Reverse leakage is specified at 100 nA maximum when the applied voltage is 114 V (76% of the nominal Zener voltage). That low leakage means the diode does not load down a high-impedance bias node before it reaches the breakdown region — important in timing circuits or start-up sequences where the voltage ramps slowly. If the diode sees forward conduction during a surge or reverse-polarity event, that drop is the clamping voltage — the circuit must survive the resulting power dissipation until the fault clears.