Electronics > Beginners
Lm317 vs LM338
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David Hess:
I have never had any problem with genuine LM350s or LM338s.  They have always operated as higher current and power LM317s like they should.
mikerj:

--- Quote from: Mr. Scram on August 26, 2019, 03:33:28 am ---
--- Quote from: Audioguru again on August 26, 2019, 03:10:53 am ---A real LM338 will shut down safely if it is overloaded and gets too hot. A fake one might simply melt into a short circuit.
EDIT: An LM338 at Digikey costs less than a cheap McDonalds hamburger.

--- End quote ---
If you include shipping the difference can be 1000%

--- End quote ---

Who orders a single cheap component?  You order a bunch of stuff you need to make the most of the postage.
dcbrown73:
There seems to be a disconnect here between people who do EE for a living and those who only do it as a hobby.   Your normal hobbyist doesn't use 100 LM338 transistors in any type of reasonable time frame nor can all of them afford to buy all possible components they may need in their hobby in bulk.  (not to mention finding a place a to store a huge inventory of components in any type of organized manor in a corner of your bedroom or whatever.

I try to order in lots of 10, but my problem is that today's learning experiment has me ordering 5 different components and as I learn something new.  It leads me to another learning experiment that has me ordering three more components again two days later.  (a major reason I buy resistor / transistor / cap / etc bulk kits, but alas those are normally Chinese kits)  All the sudden I find my self needing to order 3-4 times in two weeks as my learning moves forward.   At $9-$12 per shipment.   All the sudden I'm getting close to $50 is shipping alone in two weeks.

It would be nice if I knew everything I would need for a month or two in advance.  I could save a lot of money over the course of a year for maybe a new Keysight scope!
schmitt trigger:
I am also a little dumbfounded by these failures. I built many power supplies utilizing the LM338 without problems.
The only points you should be well aware of are:
-Ensure the minimum 10 mA load current, as Audioguru explained. But that in itself won't cause a failure.
-Use the antiparallel diode, as recommended in the datasheet, to prevent the output capacitor from discharging into the regulator.
-Keep the ground (common) wiring short, use thick wires. A star-grounding system also helps.

Of course, if the devices are fakes, this will not prevent the damage.
exe:

--- Quote from: dcbrown73 on August 26, 2019, 01:54:45 pm ---All the sudden I find my self needing to order 3-4 times in two weeks as my learning moves forward.   At $9-$12 per shipment.   All the sudden I'm getting close to $50 is shipping alone in two weeks.

It would be nice if I knew everything I would need for a month or two in advance.  I could save a lot of money over the course of a year for maybe a new Keysight scope!

--- End quote ---

That's why I tend to buy a lot of stuff that I don't use in the end to save on shipping and waiting.

I used to be upset about it, now I just call it "price for education". Unless you are really short of money, I don't see $50 as a big expense. I myself can save much more just by stop buying junk food, alcohol, etc.

Anyway, I'm yet to finish a project without a need to order missing parts last minute. I just accept that I'll have to do an additional order or two. My annual budget for this hobby is $XXXX (amount removed not to shock people) (it's ok to spend less, it's the amount I allow myself without hesitation). It's big money, and people tell I'm crazy, but I think it's fine to pay so much for own education. Who said it should be for free? Last year I didn't spend much because most of the time I already have parts and equipment I need. I spend my money, but when I was a child my parents just gave pocket money so I could buy spare parts from the flea market because they thought that would facilitate development of my tech skills that would make me more competitive on the job market.

So, I suggest optimize for speed of learning and development, and not put unnecessary budget constraints that limits you. Save on beer, but not on parts.
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