How to bring down the LT3080 to 0V output

[konfu]

Hi folks,

I am trying to build my own bench top power supply (like quite a few people on the forum) and I ran into an issue about the LT3080's output voltage:

It doesn't go down to what the theoretical minimum should be: 0V !!

Why: Well - there is this 1mA current source occupying some millivolts. Bloody hell!


After playing around with some ideas I found out (God bless Google and YouTube) that a negative feed to the LM334 might help. And well - it does ;-)

See attached schematic for your reference.

I used a CAT660 (newer version of the MAX660 or LM660) to generate a 3.3V negative voltage feeding into the former GND input of the LM334. Works like a charme!

Cheers

Florian

[ivan747]

If you are careful enough you can make an LM317 go to 0V too. You use this chip and you create a -1.25V reference. Now you put any voltage in the ADJ pin of the LM317. If you bring it down to -1.25V the output will be 0V, so theres a 1.25V offset of course. You have to use a current source like you are doing right now as well, I am guessing. If you are going to use a DAC to connect to the ADJ pin, you have to use the -1.25V as the negative reference. In fact you may have to make the -1.25V rail your digital "ground" (I think it's more of a common terminal) and make the positive supply 3.75V if you are using 5V logic.