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A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the Zener voltage, is reached. Zener diodes are manufactured with a great variety of Zener voltages and some are even variable.
In electronics, the Zener effect (employed most notably in the appropriately named Zener diode) is a type of electrical breakdown, discovered by Clarence Melvin Zener. It occurs in a reverse biased p-n diode when the electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor , leading to numerous ...
In an avalanche, one carrier collides with other atoms and knocks free new carriers. The result is that for each carrier that starts across a barrier, several carriers synchronously arrive. The result is a wide-bandwidth high-power source. Conventional diodes can be used in breakdown. The avalanche breakdown also has multistate noise.
Figure 5: Typical constant current source (CCS) using LED instead of Zener diode The Zener diode can be replaced by any other diode; e.g., a light-emitting diode LED1 as shown in Figure 5. The LED voltage drop ( V D ) is now used to derive the constant voltage and also has the additional advantage of tracking (compensating) V BE changes due to ...
The most stable diodes of this type are made by temperature-compensating a Zener diode by placing it in series with a forward diode; such diodes are made as two-terminal devices, e.g. the 1N821 series having an overall voltage drop of 6.2 V at 7.5 mA, but are also sometimes included in integrated circuits.
The Shockley diode equation relates the diode current of a p-n junction diode to the diode voltage .This relationship is the diode I-V characteristic: = (), where is the saturation current or scale current of the diode (the magnitude of the current that flows for negative in excess of a few , typically 10 −12 A).
When the absorber is in the primary circuit, e.g. a Zener diode (or LED) with voltage V z connected "backwards" across the primary windings, the current waveshape is a triangle with the time t open determined by the formula I p = I peak,m - V z ×T open /L p, here I peak,m being the primary current at the time the switch opens. When the ...
For simplicity, diodes may sometimes be assumed to have no voltage drop or resistance when forward-biased and infinite resistance when reverse-biased. But real diodes are better approximated by the Shockley diode equation, which has an more complicated exponential current–voltage relationship called the diode law.