[Nospam]

So I finally got around to sourcing parts for some of the many amp boards I've been collecting

I decided to also power some of them with a TREAD, but I'm curious about the many choices for the LM317.

Specifically, Tangent mentions the National version is better than the others (such as Fairchild, I presume). I'm just wondering what the National version gives me that the others don't. Better durability? Quality control? Performance? Peace of mind, knowing I paid for the "Best"?

The price difference isn't much, dollar-wise, but a lot percentage-wise. I'm mainly asking out of curiosity.

 

[tangent]

My hero, Bob Pease, invented it as an employee of National many decades ago. National made it famous, and then all these other people came along and cloned it. What you're paying for from National is knowing that you're getting the same design that earned the LM317 its wide appeal in the first place. Two parts may have the same "equivalent schematic" and may meet the same datasheet specs, yet not perform the same in extrema.

 

[ericj]

I've had uniformly good luck with OnSemi, ST, and Motorola 317's.

And by that i mean that with enough fast enough capacitance in the right places, an ad-hoc layout with no features fancier than a capacitor on the adjust leg can result in no measurable ripple on the output.

I get more ripple out of the jrc (aka njm) 317's but a couple milivolts at 120hz on top of 28v doesn't result in anything i can hear or find with the 'scope on the output of my m3, for example.

But they're also easier to kill than better brands. I've fried 4 or 5 of the jrc317's doing stupid things, somehow never managed to kill any other brand.

Some guy on ebay is offering hundreds of NOS (1989) National lm317t's with bent legs (for horizontal mounting) for 30 cents each but i can't get him to fess up what his shipping rates are.

Be a real funny joke if i bought 20 of them and then find out he wants $5 for the first item & 50 cents each additional or some nonsense like that.

His lm317t's have a "P+" marking in addition to the part number and date code. I have not been able to figure out what the heck that means.

Since I'm a real cheapskate I'd be interested to know what the best 317 under 50 cents is, so i can religate my jrc317's to non-audio tasks and odd jobs like current sources.

Oh, an aside, unless I'm confused the 1085 adjustable regulators are functionally compatible, aren't they? The genuine LT1085-CT can be shockingly expensive but I've seen National's LM1085 for as little as a buck each (Allied Electronics for example).

 

[tangent]

Quote:

Originally Posted by ericj I've fried 4 or 5 of the jrc317's doing stupid things, somehow never managed to kill any other brand.

I've killed several Fairchilds. That's why I changed to Nationals in my TREAD kits recently. $1 is a bad trade for the hassle, to me.

Quote:

His lm317t's have a "P+" marking in addition to the part number and date code. I have not been able to figure out what the heck that means.

Email Bob Pease through his website. He does answer questions, and if anyone would know, he would.

Quote:

unless I'm confused the 1085 adjustable regulators are functionally compatible, aren't they? The genuine LT1085-CT can be shockingly expensive but I've seen National's LM1085 for as little as a buck each (Allied Electronics for example).

If you're asking whether the LMs and the LTs are compatible, then, yes. Linear just improved a few specs a bit is all.

If you're asking whether 1085s are directly swappable for 317s, then the answer is a highly qualified "maybe". LDO vs. standard, and output impedance differences can break a design not made with these differences in mind.

 

[Nospam]

Thanks for the quick response!

Always learning something new on this site

 

[peranders]

Remember that second source of some part isn't the same thing as an indentical part. First you have to study the datasheet but then you have also undocumented features. I have personal experience of LM324 from different manufactures. One brand had 0.6 volts as minimum output and some other had 100 mV! This was crucial in my design.

 

[NeilR]

Tangent,

I am building a Steps, which may serve several purposes, including a future Millet Hybrid and/or M3, or possibly a PPA.

I noticed that AMB highy recommends using an LM338 in place of the LM317 and it is apparently plug replaceable without any other tweaks. Any thoughts on this?

Regards,
Neil