12 V zener — 1 W rating and ±2% tolerance
The 1N4742CPE3/TR12 is a 12 V zener diode rated for 1 W continuous power dissipation in the standard DO-204AL (DO-41) axial-lead package. The ±2% tolerance band means the actual zener voltage falls between 11.76 V and 12.24 V at the specified test current — tighter than the common 5% grade, so it suits precision shunt regulation or voltage reference circuits where the rail must stay within a narrow window. Maximum zener impedance is 9 Ohms (Zzt) at the test current; this value governs how much the output voltage shifts with changing load current. The lower the impedance, the stiffer the regulation — 9 Ohms is typical for a 1 W, 12 V device in this family.
Temperature range and reverse leakage
A design running at 85°C ambient still has 65°C margin to the absolute maximum, which matters when the diode shares a board with hot-running passives or sits in an outdoor enclosure. Reverse leakage is specified at 5 µA maximum with 9.1 V applied across the junction — well below the 12 V breakdown knee. In a battery-powered reference circuit, this leakage contributes to the quiescent draw; at 5 µA it is negligible against a typical coin-cell self-discharge rate. Forward voltage is 1.2 V maximum at 200 mA forward current — the standard silicon diode drop. If the part is ever forward-biased in the application (e.g., during a reverse-polarity transient), the 1 W power rating limits the forward current to about 830 mA continuous before the die exceeds its thermal budget.
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