Editing Zener diode (section)

==Operation==
[[File:3.4V Zener diode V-A characteristic.svg|thumb|300px|Current-voltage characteristic of a Zener diode with a breakdown voltage of 3.4&nbsp;V]]
[[File:Temperaturkennlinie von Z-Dioden.svg|thumb|300px|Temperature coefficient of Zener voltage against nominal Zener voltage]]

A conventional solid-state diode allows significant current if it is [[reverse bias]]ed above its reverse-breakdown voltage. When the reverse-bias breakdown voltage is exceeded, a conventional diode will conduct a high current due to avalanche breakdown. Unless this current is limited by external circuits, the diode may be permanently damaged due to overheating at the small (localized) areas of the semiconductor junction where avalanche breakdown conduction is occurring. A Zener diode exhibits almost the same properties, except the device is specially designed so as to have a reduced breakdown voltage, the ''Zener voltage''. By contrast with the conventional device, a reverse-biased Zener diode exhibits a controlled breakdown and allows the current to keep the voltage across the Zener diode close to the Zener breakdown voltage. For example, a diode with a Zener breakdown voltage of 3.2&nbsp;V exhibits a voltage drop of very nearly 3.2&nbsp;V across a wide range of reverse currents. The Zener diode is therefore well suited for applications such as the generation of a [[Voltage reference|reference voltage]] (e.g. for an [[amplifier]] stage), or as a voltage stabilizer for low-current applications.<ref name=JM79>{{cite book |first=Jacob |last=Millman |title=Microelectronics |publisher=McGraw Hill |year=1979 |isbn=978-0071005968 |pages=[https://archive.org/details/microelectronics00mill/page/45 45–48] |url=https://archive.org/details/microelectronics00mill/page/45 }}</ref>

Another mechanism that produces a similar effect is the avalanche effect as in the [[avalanche diode]].<ref name=JM79/> The two types of diode are in fact constructed in similar ways and both effects are present in diodes of this type. In silicon diodes up to about 5.6&nbsp;volts, the [[Zener effect]] is the predominant effect and shows a marked negative [[temperature coefficient]]. Above 5.6&nbsp;volts, the avalanche effect dominates and exhibits a positive temperature coefficient.<ref name=Dorf93>{{cite book |editor-first=Richard C. |editor-last=Dorf |title=The Electrical Engineering Handbook |publisher=CRC Press |location=Boca Raton |year=1993 |isbn= 0-8493-0185-8 |page=457}}</ref>

In a 5.6&nbsp;V diode, the two effects occur together, and their temperature coefficients nearly cancel each other out, thus the 5.6&nbsp;V diode is useful in temperature-critical applications. An alternative, which is used for voltage references that need to be highly stable over long periods of time, is to use a Zener diode with a temperature coefficient (TC) of +2&nbsp;mV/°C (breakdown voltage 6.2–6.3&nbsp;V) connected in series with a forward-biased silicon diode (or a transistor B–E junction) manufactured on the same chip.<ref>{{cite book|title=Calibration: Philosophy in Practice |isbn=0963865005 |publisher=Fluke |year=1994 |pages=7–10}}</ref> The forward-biased diode has a temperature coefficient of −2&nbsp;mV/°C, causing the TCs to cancel out for a near-zero net temperature coefficient.

It is also worth noting that the temperature coefficient of a 4.7&nbsp;V Zener diode is close to that of the emitter-base junction of a silicon transistor at around −2&nbsp;mV/°C, so in a simple regulating circuit where the 4.7&nbsp;V diode sets the voltage at the base of an NPN transistor (i.e. their coefficients are acting in parallel), the emitter will be at around 4&nbsp;V and quite stable with temperature.

Modern designs have produced devices with voltages lower than 5.6&nbsp;V with negligible temperature coefficients,{{citation needed|date=February 2013}}. Higher-voltage devices have temperature coefficients that are approximately proportional to the amount by which the breakdown voltage exceeds 5&nbsp;V. Thus a 75&nbsp;V diode has about ten times the coefficient of a 12&nbsp;V diode.{{citation needed|date=November 2017}}

Zener and avalanche diodes, regardless of breakdown voltage, are usually marketed under the umbrella term of "Zener diode".

Under 5.6&nbsp;V, where the Zener effect dominates, the IV curve near breakdown is much more rounded, which calls for more care in choosing its biasing conditions. The IV curve for Zeners above 5.6&nbsp;V (being dominated by avalanche), is much more precise at breakdown.