[sdiy] Negative voltage references

[Magnus Danielson]

On 05/19/2012 05:37 PM, Olivier Gillet wrote:
> If you don't need more than +/- 5% precision and, you can simply use a
> Zener. 4.7V or 5.1V have nearly null temperature coefficients. I use
> 1N5230B. This kind of precision is OK for getting a negative offset
> voltage for a VCF - in a CV scaler for a SSM2164 for example. Just
> make sure the resistor is low enough and that at least 1mA is flowing
> through the diode - otherwise it won't reach the Zener voltage.
>
> I think shunt voltage references can be used as negative references
> too. Just tried wiring a LM4040 backwards and it worked. Not
> explicitly mentioned in the LM4040 datasheet, but I've already seen
> that in the datasheet of other shunt references like the ADR540B.

There exists bandgaps which you use just like a zener, so putting them 
on the negative side would work just as well. Look at the classic TL431 
for instance. Naturally, none of the examples I see uses it for negative 
regulation, but most of them should be trivial to setup.

The TL431 has an internal 2,75 V reference, and then a resistor pair 
hooked up across the "zener" to a third terminal scales this 2,75 V.

Cheers,
Magnus