[Amps] Zener Bias Replacement

[Tom W8JI]

>I can never remember which way round the TC goes, but below 
>about 5 and a bit volts, it's Zener breakdown, and above 
>that, it's avalanche breakdown. Because of the turnover, at 
>about 5.6 to 6 volts, the TC is essentially zero.

That's why I always pick 5v Zeners for voltage references 
when possible.

There's another issue with a string of diodes besides 
temperature. They change voltage with forward current.

I'm sure diodes are all different, but I measured a string 
of ten 1N4005 diodes in series last night.

Room temp:
100mA 7.59v
500mA 8.21 volts

After running 500mA through them for 2 minutes:

100mA 7.07 volts
500 mA 7.64 volts

It doesn't appear to be that wonderful of an idea at first 
glance.

Anyone else have any actual measurements? Has anyone 
actually checked the bias stability of various diodes? 100mA 
7.07v up to 500mA 8.21v doesn't seem so wonderful. That's 
with NO external heating.

73 Tom