Editing Zener diode (section)

==Uses==
[[File:Zener 3D and ckt.png|right|100px|thumb|Zener diode shown with typical packages. ''Reverse'' current <math>-i_Z</math> is shown.]]
Zener diodes are widely used as voltage references and as [[Shunt (electrical)|shunt]] [[voltage regulator|regulators]] to regulate the voltage across small circuits. When connected in parallel with a variable voltage source so that it is reverse biased, a Zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. From that point on, the low impedance of the diode keeps the voltage across the diode at that value.<ref name=PHWH89>{{cite book |first1=Paul |last1=Horowitz |first2=Winfield |last2=Hill |title=The Art of Electronics |edition=2nd |publisher=Cambridge University Press |year=1989 |isbn=0-521-37095-7 |pages=[https://archive.org/details/artofelectronics00horo/page/68 68–69] |url=https://archive.org/details/artofelectronics00horo/page/68 }}</ref>

[[File:Zener diode voltage regulator.svg|220px|center]]

In this circuit, a typical voltage reference or regulator, an input voltage, ''U''<sub>in</sub> (with + on the top), is regulated down to a stable output voltage ''U''<sub>out</sub>. The breakdown voltage of diode D is stable over a wide current range and holds ''U''<sub>out</sub> approximately constant even though the input voltage may fluctuate over a wide range. Because of the low impedance of the diode when operated like this, resistor ''R'' is used to limit current through the circuit.

In the case of this simple reference, the current flowing in the diode is determined using Ohm's law and the known voltage drop across the resistor ''R'';
:<math>I_\text{diode} = \frac{U_\text{in} - U_\text{out}}{R}</math>

The value of ''R'' must satisfy two conditions:
# ''R'' must be small enough that the current through D keeps D in reverse breakdown. The value of this current is given in the data sheet for D. For example, the common BZX79C5V6<ref>{{cite web|url=http://www.fairchildsemi.com/pf/BZ/BZX79C5V6.html |title=BZX79C5V6 − 5.6V, 0.5W Zener Diode – data sheet |publisher=Fairchild Semiconductor |access-date=July 22, 2014}}</ref> device, a 5.6&nbsp;V 0.5&nbsp;W Zener diode, has a recommended reverse current of 5{{nbsp}}mA. If insufficient current exists through D, then ''U''<sub>out</sub> is unregulated and less than the nominal breakdown voltage (this differs from [[voltage-regulator tube]]s where the output voltage is higher than nominal and could rise as high as ''U''<sub>in</sub>). When calculating ''R'', allowance must be made for any current through the external load, not shown in this diagram, connected across ''U''<sub>out</sub>.
# ''R'' must be large enough that the current through D does not destroy the device. If the current through D is ''I''<sub>D</sub>, its breakdown voltage ''V''<sub>B</sub> and its maximum power dissipation ''P''<sub>max</sub> correlate as such: <math>I_D V_B < P_\text{max}</math>.

A load may be placed across the diode in this reference circuit, and as long as the Zener stays in reverse breakdown, the diode provides a stable voltage source to the load. Zener diodes in this configuration are often used as stable references for more advanced voltage regulator circuits.

Shunt regulators are simple, but the requirements that the ballast resistor be small enough to avoid excessive voltage drop during worst-case operation (low input voltage concurrent with high load current) tends to leave a lot of current flowing in the diode much of the time, making for a fairly wasteful regulator with high quiescent power dissipation, suitable only for smaller loads.

These devices are also encountered, typically in series with a base–emitter junction, in transistor stages where selective choice of a device centered on the avalanche or Zener point can be used to introduce compensating temperature co-efficient balancing of the transistor [[p–n junction]]. An example of this kind of use would be a DC [[Error amplifier (electronics)|error amplifier]] used in a [[regulated power supply]] circuit feedback loop system.

Zener diodes are also used in [[surge protector]]s to limit transient voltage spikes.

=== Noise generator ===
Another application of the Zener diode is using its [[avalanche breakdown]] [[Noise (electronics)#Avalanche noise|noise]] (see {{Slink|noise generator|Zener diode}}), which for instance can be used for [[dithering]] in an [[analog-to-digital converter]] when at a [[Root mean square (RMS) amplitude|rms level]] equivalent to {{Fraction|1|3}} to 1 [[Least Significant Bit|lsb]]<ref>{{Cite book |last=Lyons |first=Richard |url=https://www.mikrocontroller.net/attachment/341426/Understanding_digital_signal_processing.pdf |title=Understanding Digital Signal Processing |publisher=[[Prentice Hall]] |year=2004 |isbn=0-13-108989-7 |edition=2nd |location=Upper Saddle River, New Jersey |pages=509 |language=en |orig-date=2001 |archive-url=https://web.archive.org/web/20230405030831/https://www.mikrocontroller.net/attachment/341426/Understanding_digital_signal_processing.pdf |archive-date=2023-04-05 |url-status=live}}</ref> or to create a [[Hardware random number generator|random number generator]].

===Waveform clipper===
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Two Zener diodes facing each other in series clip both halves of an input signal. [[Clipper (electronics)|Waveform clippers]] can be used not only to reshape a signal, but also to prevent voltage spikes from affecting circuits that are connected to the power supply.<ref name="Electronic Devices">{{cite book|last=Diffenderfer| first=Robert|title=Electronic Devices: Systems and Applications |year=2005 |publisher=Thomas Delmar Learning |isbn=1401835147 |pages=95–100 |url= https://books.google.com/books?id=Bs6sz1TlfaIC&q=waveform+clipper+zener+diode&pg=PA94 |access-date=July 22, 2014}}</ref>

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===Voltage shifter===
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A Zener diode can be applied to a circuit with a resistor to act as a voltage shifter. This circuit lowers the output voltage by a quantity that is equal to the Zener diode's breakdown voltage.

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===Voltage regulator===
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A Zener diode can be applied in a [[voltage regulator]] circuit to regulate the voltage applied to a load, such as in a [[linear regulator]].

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