Re: Low voltage zener diodes

On a sunny day (Wed, 9 Oct 2024 01:40:46 +0530) it happened Pimpom
<Pimpom@invalid.invalid> wrote in <algNO.58718$zcoc.57968@fx10.ams1>:

On 08-10-2024 07:25 pm, Jan Panteltje wrote:

On a sunny day (Tue, 8 Oct 2024 14:54:39 +0530) it happened Pimpom
<Pimpom@invalid.invalid> wrote in <sT6NO.84691$Xx4a.59580@fx11.ams1>:
 

When I tested some low voltage zener diodes (<<5V) 30-40 years ago, I
found that they didn't have even a reasonably sharp knee, behaving more
like LEDs in forward mode, maybe worse. Do I remember correctly? Are
they still the same?

 
Yes.
These days there  are 'bandgap' references, those are about 1.25V,
extr3mely stable.
  https://en.wikipedia.org/wiki/Bandgap_voltage_reference
You can also use a chip like TL431 (google TL431.pdf)
to make a reference from about 2.5 V upwards
to whatever you like with 2 resistors as voltage devider.
IIRC it uses that bandgap reference principle.
  https://en.wikipedia.org/wiki/TL431#Applications
 
 

I have a bunch of TL431, LM385 (1.25, 2.5 & adj.) and LM4040 references.
But somehow these high precision, high stability references somehow feel
like overkill in certain situations. It's not the cost, it's the
appropriateness.

Sure, my PIC programmer uses LEDs in series as voltage reference :-)

I remember the first time I used an LM385. I live in a very remote, very
hilly part of India. 30-40 years ago, most of the rural areas in my
state was powered by 300kVA diesel generators. The generators were made
by an Indian company but the voltage regulators were imported and cost
the then equivalent of about US$4-5000 to replace. Moreover, the
manufacturer sometimes took months to supply a replacement.
>
So I designed and made several units for the state power agency, using
only readily available parts. That's where I used LM385s as the
reference. I had to make some of the parts by hand - like the EMI
filter, the box, PCB, etc. The only material available then for weather
proofing was small tubes of Araldite epoxy intended for domestic
consumer use.

It is nice to be able to design with what you can get, is awailable.