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Zener diode application...

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jameslee

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:grin: Hi everyone, I'm kinda new to zener diode and wish to ask expert here for some guidance.

usually i only use zener as temporary overvoltage protection, but there are some occasion i use zener to bias a transistor for non critical power supply.

These are some of the things i dont understand much:

1) What is the difference between normal zener diode and silicon planar zener diode?
2) why zener diode rated by Zzk,resistance. In which occasion does zener resistance is important?
3) some zener breakdown voltage are more "resistance" towards Izk changes, as if even if Izk change, the breakdown voltage still remain more or less the same, but which parameter in datasheet specify this characteristic?because not all datasheet shoes I-V curve of zener at breakdown region.

sorry if i'm asking dump question, I dont have much understanding in zener diode application.
Thanks in advance for all of your help.

James
 

FvM

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- all "normal" zener diodes are silicon planar zener diodes, I think
- Rzk or Zzk (the dynamical resistance or dU/dI) is in fact specifying the regulation quality
- there's no standard specification scheme. You'll e.g. find different reference currents between manufacturers. Manufacturers avoid to specify parameters that aren't exactly related to the standard usage, although may be important for you, e.g. typical leakage current at lower voltage.
 

LvW

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Hi James, for my opinion the key to understand the properties as well as application principles for Z-diodes is the following:

The I-V charactristic of a Z-diode is strong non-linear leading to the necessity to discriminate between static and dynamic (differential) resistances.
In particular, the Z-diode has a
*static resistance Rz=Vz/Iz, which can be between medium and large (ohm...kohm range) with Vz approximately identical to the breakdown voltage,
*rather small dynamic resistance rz=dVz/dIz (because of the steep I-V curve), which can be rz=1 ohm or even less.

The value of rz depends on the Z-diode type, the chosen breakdown voltage (rz smallest around Vz=6.5 volts) as well as on the selected operational point, which is determined by the dc current Iz.
 
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