[sdiy] Negative voltage references

Tom Wiltshire tom at electricdruid.net
Sun May 20 00:10:00 CEST 2012


On 19 May 2012, at 18:53, David G Dixon wrote:

>> Ideally, anything you hang off it will need to be via an op 
>> amp buffer.
> 
> That's really important.  One must take a close look at the current specs
> for whatever is used.  LM4040 is pretty low.  REF02 is better.
> 
> For me personally, the best practice is to buffer and invert any reference
> voltage with a dual opamp, and then you can use any single positive
> reference and you don't have to worry about it.

Ok, so the advantage of the "cheap regulator" over the "expensive reference" would be that you don't need any buffer, since a voltage regulator can provide as much current as you're likely to need. After all, you could easily spec the regulator for 1A or more. The disadvantage is that the regulation isn't that good, especially if the load is low. I've got a L7905CV on my breadboard which is supposed to be producing -5V and is actually producing -6.8V. I expect it would improve a great deal if I stuck an LED across it, but it seems a bit crazy. I wanted to use a 79L05 but didn't have one to hand, so used the "next nearest".
Hence the original question about negative voltage references.

Thanks,
Tom







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