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Why do we not see Zener diodes used in series as a voltage dropper?
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silicon junkie:
Here’ a question: Why do we not see Zener diodes used in series as a voltage dropper?
Assuming minimum forward current and max dissipation is observed it should be ok but I don’t think I have ever seen it done
Standard diodes are sometimes used but if you want to drop more than a volt or two then a string of them becomes impractical.
My practical use is to reduce the power dissipation (edited: by about 500mW) in a SMT regulator by sharring it with a 3.9v series zener.
Any ideas why we never see this done in practice?
OM222O:
at low currents the power dissipation of an LDO is minimal, so nothing is needed.
at moderate currents, usually 1 or 2 volts of drop helps significantly, so normal diodes / resistors are used (resistor needs to be calculated for optimal performance).
at high currents, either a tracking pre-regulator is used for efficiency reasons (usually buck converter) or if you don't care about efficiency at all, again a resistor does much better that diodes. zeners are useless for this sort of power applications. let's say you want to drop 2 volts at 1A (which is very conservative, usually the voltage difference or current should be higher to use resistors!), that means 2 watts of power. I'm not sure if zeners with that power rating even exist, and if they do, they will be much much more expensive than even a SMD 5watt resistor.

simply put: in non of the conditions a zener makes any sense.
ArthurDent:
Scroll down in this article to see zeners wired in series. Probably the reason they aren't used more in series is that it is so easy to make a variable supply using one of the cheap 3-terminal regulators.

https://www.electronics-tutorials.ws/diode/diode_7.html
hv222:
Zener diodes are used in series as a voltage dropper. Check out this application note: https://www.analog.com/media/en/technical-documentation/application-notes/an92f.pdf (figure 8 and 15). Zener diodes are used to drop voltage, before current sensing resistor to match maximum input voltage of operational amplifier.
SteveyG:
They are regularly used in this manner. Absolutely nothing wrong with it
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