[sdiy] Negative voltage references

David G Dixon dixon at mail.ubc.ca
Sun May 20 20:48:21 CEST 2012

> How do you deal with the minimum current requirement in your 
> 2164 VCAs, David?

Honestly, I wasn't aware of this requirement.  It isn't explicitly stated in
the datasheet, other than by the fact that 1 mA appears as a lower limit in
the voltage spec table entries.  This could mean simply that they only
measured it over that range.  There is a plot in the datasheet which shows
dropout voltages down to 0 mA output current, and which aren't that
different from those at 10 mA.

In my VCA circuit, I've got six 100k resistors to ground from the 79L05, so
I'm only pulling about 0.3 mA.  I just measured the output of the 79L05, and
it was -5.03V.  When I put a 4.99k resistor from the output to ground, thus
bringing the output current to 1.3 mA, the output voltage went to -5.03V.
No change within the accuracy of my DVM.

I would say that this is not worth losing sleep over.

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