LT3080 alternative

[bitshift]

Hey everyone,

Please forgive me if this has been previously addressed, but I'm currently building a power supply and I am using Daves uSupply design as a reference.

I am currently using an LM317 but I'm finding that the 1.25 difference between the set pin and the output to be quite a pain when driving the set pin with a DAC through a buffer.

Apparently the LT3080 has a few issues as discussed here https://www.eevblog.com/forum/projects/lt3080-wierdness-dave's-power-supply-(eev224)-gone-mad/.

So I'm looking for a regulator similar to LT3080 which has a constant current source as apposed to a reference voltage.

Any suggestion will be most welcomed.

[cellularmitosis]

You can't use the LT3083?  I thought it didn't suffer from the same problem (and you get more current handling)

[Xenon Photon]

You may use a digital potentiometer instead of DAC and buffer.

http://en.wikipedia.org/wiki/Digital_potentiometer

[ivan747]

I've heard the LT3081 doesn't have this problem. Aditionally it has some niceties, like a temperature monitoring pin and a current adjust pin (not very precise but very cool).

[0xdeadbeef]

Speaking of the LT3081: I wonder if the current monitoring output is good enough to use for the current regulation.
I.e. to save the highside current monitor and use the monitoring output as "is" value for the current limit comparator.

[chickenHeadKnob]

When comparing LT3080      dropout voltage 0.35V
                            LT3081                                1.21V <--- gotcha for young players think it indicates NPN bypass stage
                            LT3082                                1.3
                            LT3083                                0.31

Dave said in his video's back then that the 3080 was the new and improved and natural successor to the LM317, but the spec sheet of the LT3081 would seem to me a better match (current carrying and otherwise)

[tszaboo]

Dave said in his video's back then that the 3080 was the new and improved and natural successor to the LM317, but the spec sheet of the LT3081 would seem to me a better match (current carrying and otherwise)

It will be the sucessor, when it will not cost 20 times more than the LM317.

[bitshift]

Thanks for the suggestions guys.

The LT3081 looks really awesome. Unfortunately the LT parts don't seem to be freely available here in South Africa. I could source them but a hefty premium.

[ivan747]

Speaking of the LT3081: I wonder if the current monitoring output is good enough to use for the current regulation.
I.e. to save the highside current monitor and use the monitoring output as "is" value for the current limit comparator.

I wondered too. The current monitoring is not great, it only gives you a rough indication, it's +10%/-5% accurate. I don't think it's going to be stable with temperature either. The current limit is reasonably stable from 20 degrees C and up to 100. From 20 degrees C and below it gets inaccurate and that's why the spec is so bad on the "electrical characteristics" table. (look at the "Programmable Current Limit" graph, LT3081 datasheet). For bench power supply purposes it would be okay unless you want to do a really proper job and you want to compete with good commercial units.

TL,DR: The current limiting feature is good only if you use it on the 25 to 100 degrees C range. That might apply to the voltage regulation as well, in general, try to keep the device at a constant temperature, maybe with a fan, and you should get stable settings after the thing warms up.

[ivan747]

Thanks for the suggestions guys.

The LT3081 looks really awesome. Unfortunately the LT parts don't seem to be freely available here in South Africa. I could source them but a hefty premium.

They are like that, Linear is a very good brand for power regulation stuff.
Personally, if it's only for a project that I am going to do once or twice in my life, I don't care about the choice of ICs. If I am going to sell many I look for cheap parts. If I have plans to share it with people from latin america, then I try to use generic parts, because if we can't buy it in the street market, then it's a pain to import them and many people won't be bothered.