Adjustable voltage source from 0 to 12V

lt?

Take a look at the National Semiconductor applications notes for 317. You'll find that by adding a small negative power supply, you can go down to the ground rail.

Steve

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.

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.

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.

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

lt?

You might look at the the National Semiconductor LM395 "ultra reliable power transistor" which does include thermal protection.

-- Bill Sloman, Nijmegen

On a sunny day (Sun, 07 Feb 2010 22:54:03 +0100) it happened OBones wrote in :

If regulation is not that important just put 2 Si diodes in series with the output...

lt?

Sounds like the LT3080 might fit your bill.

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

George H.

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

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

There a number of power supply circuits on

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

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.

But you need a negative supply. Perhaps a good place for a charge pump, since the current needs of the ADJ pin are less than 100uA. ...Jim Thompson

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)-----|