Adjustable voltage source from 0 to 12V

[OBones]

Hello,

Using a LM317, I can create an adjustable voltage supply without much
complexity, but it cannot go lower than 1.25V
Would you know some equivalent IC that would allow to go down to 0.001 volt?
It doesn't need to supply much more than 100mA but it would be nice if
it was thermally protected like the LM317.

Regards

 

[Fred Bartoli]

OBones a écrit :

Hello,

Using a LM317, I can create an adjustable voltage supply without much
complexity, but it cannot go lower than 1.25V
Would you know some equivalent IC that would allow to go down to 0.001
volt?
It doesn't need to supply much more than 100mA but it would be nice if
it was thermally protected like the LM317.

Regards

Make your own with an opamp and use the LM317 as the power pass element.

 

[mike]

OBones a écrit :

Make your own with an opamp and use the LM317 as the power pass element.

I'd like to see your favorite circuit for this. The one you built and
extensively evaluated. Short circuit, open circuit, drive output
positive, drive output negative, load dump, input voltage dump,
transient response...the usual stuff.

Every time I've thought about doing this, it got real complex real fast.

 

[Jamie]

Hello,

Using a LM317, I can create an adjustable voltage supply without much
complexity, but it cannot go lower than 1.25V
Would you know some equivalent IC that would allow to go down to 0.001
volt?
It doesn't need to supply much more than 100mA but it would be nice if
it was thermally protected like the LM317.

Regards

Have you tried offsetting the common from the supply via 2 diodes?
You may need to put a limit R at the low side of the voltage set pot
to prevent - voltage at zero set point.

This should work if the supply operating the 317 is of it's own via a
xformer etc..
In other words, you're not using an external supply with a common that
could come in contact with other components.

 

[Adam Seychell]

I'd like to see your favorite circuit for this. The one you built and
extensively evaluated. Short circuit, open circuit, drive output
positive, drive output negative, load dump, input voltage dump,
transient response...the usual stuff.

Every time I've thought about doing this, it got real complex real fast.

And that's why most power sources do not include all of the above
features. Some fault protection are easy (e.g negative input), while
others (e.g negative output drive) are not so easy to implement,
especially at higher power levels.

 

[ehsjr]

Hello,

Using a LM317, I can create an adjustable voltage supply without much
complexity, but it cannot go lower than 1.25V
Would you know some equivalent IC that would allow to go down to 0.001
volt?
It doesn't need to supply much more than 100mA but it would be nice if
it was thermally protected like the LM317.

Regards

David Jones discussed a chip that does what you want
in his first EEVBLOG: the LT3085 from Linear Technologies

I've used it, and it does indeed go down to 0 volts,
but I didn't need precision of 1 mV so I didn't test
it that closely.

Ed

 

[OBones]

David Jones discussed a chip that does what you want
in his first EEVBLOG: the LT3085 from Linear Technologies

I've used it, and it does indeed go down to 0 volts,
but I didn't need precision of 1 mV so I didn't test
it that closely.

This one looks good, thanks for the tip.
And it even has a SPICE model, that's really good.

 

[OBones]

Sounds like the LT3080 might fit your bill.

It's got a constant current output, and you 'program' the voltage with
a resistor.

Ah yes, seems like it is the bigger brother of the LT3085. Nice set of
components here

 

[Baron]

Richard Torrens (News) Inscribed thus:

There a number of power supply circuits on
http://www.4qdtec.com/index.html
using transistors.

Fine ! If you are prepared to pay for membership. Google gets better
info.

 

[Spehro Pefhany]

Richard Torrens (News) Inscribed thus:


Fine ! If you are prepared to pay for membership. Google gets better
info.

If you're doing a motor controller, membership is cheaper than one set
of blown power devices. ;-)


Best regards,
Spehro Pefhany

 

[Ecnerwal]

Using a LM317, I can create an adjustable voltage supply without much
complexity, but it cannot go lower than 1.25V
Would you know some equivalent IC that would allow to go down to 0.001 volt?
It doesn't need to supply much more than 100mA but it would be nice if
it was thermally protected like the LM317.

Last I recall, the LM317 application notes include this circuit - all
you need is to pull the reference negative. Page 16 of the PDF, typical
applications, 0-30V regulator. LM317 datasheet is really LM117 datasheet
(they are a family). National Semi website or your favorite source of
datasheets.

 

[Jamie]

Last I recall, the LM317 application notes include this circuit - all
you need is to pull the reference negative. Page 16 of the PDF, typical
applications, 0-30V regulator. LM317 datasheet is really LM117 datasheet
(they are a family). National Semi website or your favorite source of
datasheets.

If the supply for the reg isn't being used for anything else, you can
lift the (-) side via 2 SI diodes. On the other side of these diodes
then becomes your common (-) to every thing else..

The drop maybe a little more than needed thus giving you a little
(-) voltage out when setting the level to 0 how ever, one can simply
use an internal pot on the low side of the external pot to prevent any
less than 0.

This is all nice and rosy how ever, you will lose the amount of
voltage at the top that you shift at the bottom. If this isn't going to
be an issue, then you're all set..


(- side of supply)-----|<---|<------( this now becomes the COM to the
reg and and out side world)

some people use ZENERS to pull this trick off when needing some (-)
voltage