A zener or breakdown diode uses the Zener effect to affect current flow backward, from anode to cathode, when the voltage across its terminals exceeds the Zener voltage.
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Properties
Properties
[4.1] Like normal diodes, except they're made to have a low and specified reverse breakdown voltage using the reverse voltage used to it.
In forward-biased direction, a zener diode's anode is more positive than its cathode, like a normal diode if the forward voltage VF across is exceeds 0.7 V (silicon) causing it to conduct.
Current voltage characteristics
Current voltage characteristics
[4.1], [5.1] A zener diode's static current-voltage (I-V) characteristic depicts how it acts in different voltages. Its IV curve has 2 main regions:
In forward region, a zener diode acts like a normal diode, when voltage (Vf) has current flowing if the used forward voltage is ~+0.7 V (for silicon diodes). The current rises exponentially then, like normal diodes.
In reverse bias region, the diode blocks current, like normal diodes, til the reverse voltage passes the zener voltage (Vz) or breakdown voltage.
Once reverse voltage passes, the breakdown voltage (~3 V to many hundred volts), the diode enters reverse breakdown, letting current to flow while keeping a ~constant voltage (used for voltage regulation).
The point a zener voltage triggers current to flow through the diode is accurately controlled (to less than 1% tolerance) in the doping stage of diodes semiconductor construction giving the diode a specific zener breakdown voltage, ( VZ ) e.g., 4.3V or 7.5V. This zener breakdown voltage on the I-V curve is almost a vertical straight line.
But unlike usual diodes blocking current if reverse biased, (its cathode is more positive than anode), as the reverse voltage reaches a predetermined value, the zener diode conducts in reverse direction.
Since a zener diode works in reverse breakdown region of its characteristic curve, they have a fixed breakdown voltage, VZ value, found during manufacture. As the reverse voltage across a zener diode rises from 0 V to its zener breakdown voltage, a big reverse or leakage current flows through the diode which stays constant as the reverse voltage rises.
The forward current going through the conducting diode is at its max found only by a connected load, so in forward-bias direction, the diode acts like a usual diode in its current and/or power limits and as such, a diode's forward trait is often of no interest.
of not interest: what unengaging/boring
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Zener diode regulator
Zener diode regulator
A Zener diode regulator is a basic circuit using a zener diode's unique reverse breakdown trait to keep a constant voltage. Its zener diode connect in reverse bias to regulate the output voltage.
[5.1] Zener diodes can make a stabilised voltage output via low ripple under varying load current conditions. By passing a small current through the diode from a voltage source, via a suitable current limiting resistor (RS), the zener diode will conduct sufficient current to maintain a voltage drop of Vout.
Recall DC output voltage from a half or full-wave rectifiers has ripple superimposed onto the DC voltage and that as the load value changes so to does the average output voltage. By connecting a simple zener based stabiliser circuit as shown below across the output of the rectifier, a more stable output voltage can be produced.
[1.1] The Zener effect is a type of electrical breakdown, found 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 free minority carriers which suddenly increase the reverse current.[1]
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