EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: David Aurora on January 08, 2025, 02:42:43 am
-
Just a quick heads up in the hope nobody else loses hours of time like I just did- these "new" LM317K regulators they have in stock don't even come close to meeting spec https://www.digikey.com.au/en/products/detail/evvo/LM317K/25188516 (https://www.digikey.com.au/en/products/detail/evvo/LM317K/25188516)
I just watched 3 in a row eat shit in a bog standard regulator circuit as soon as current draw exceeded around 1A. Not a thermal thing either, in every case they worked unloaded or at half an amp or so but died instantly once I increased the load.
I don't think I've ever gotten fake parts from Digikey before so I spent ages double checking everything around them but couldn't find an issue. Then when I threw in some replacements from a different brand the power supply fired up like it's supposed to and has already been stress tested hard for about an hour without a hiccup.
Digikey were super fast with their response and have already credited me for the purchase, but who knows how long they'll still be up on the site for purchase so take my advice and don't touch them with a ten foot pole.
-
What was input voltage?
-
EVVOSEMI?
There have been a unknown and unheard of manufacturers making their way onto Digikey recently. :--
search on Digikey, I always narrow down the manufacturer.
to-3 maybe hard to find.
TI is $130 :wtf: very expensive :palm: maybe Hi-rel products.
-
I had exactly the same problem with TO-3 317s from another vendor: they would pop immediately when the load current exceeded a critical value. They should have gone into thermal limiting and survived. I’ll try to find the details.
-
WTF the EVVOSEMI schematic pass transistor is not a Darlington, but has Sziklai pair which smells like the '1117 but it's a lower voltage IC.
LM317K STEEL I used back in the late 1970's in my first power supply, a faithful horse.
-
one of the biggest features the LDO has going for it is the thermal shutdown. Its like the only reason you would parallel up LDO instead of using a pass transistor. !!
I would not call it out of spec, I would call it defective.
I use those parallel circuits that are shown in some data sheets because... each chip has a integrated over temp protection. you lose the feature when you start going with external transistors. In this case, if it breaks, why the hell would you bother??
big fail :-BROKE
-
What was input voltage?
Nah it was not an input/output voltage issue. This is from a mixing console that had survived with the original regulators for 30 years (it failed after the owner shorted something on a DIY servicing attempt) and with a different brand of regulators appears fine too. Issue is specific to these ones Digikey are selling.
-
EVVOSEMI?
There have been a unknown and unheard of manufacturers making their way onto Digikey recently. :--
search on Digikey, I always narrow down the manufacturer.
to-3 maybe hard to find.
TI is $130 :wtf: very expensive :palm: maybe Hi-rel products.
Yeah these were literally the only stocked version of the LM317K I could find from a reputable source unfortunately, usually I'd never touch an unknown brand like that. Who'd have thought I'd have had better results buying off eBay :-//
-
Who'd have thought I'd have had better results buying off eBay :-//
Maybe better or maybe same :P
WTF the whole thing, including DigiKey not noticing that this isn't even claimed to be a true 317 circuit. Maybe it went into suicidal oscillation with whatever capacitors are present in the circuit? (Assuming that the schematic found by floobydust actually represents what's inside - 1117 is not as stable as 317).
-
WTF the EVVOSEMI schematic pass transistor is not a Darlington, but has Sziklai pair which smells like the '1117 but it's a lower voltage IC.
LM317K STEEL I used back in the late 1970's in my first power supply, a faithful horse.
Maybe the battery that supplies the non-inverting reference of the current limiter is dead...
-
Another option is the LT317K, LT317AK. I dumpster dived some new LT338AK from work, if you're in a pickle (jar) let me know. But these have much greater output current.
Many smaller Taiwan and china semi manufacturers are using the classic part number but selling you a "cost improved" redesigned part.
Example I got comparators slow as molasses 10usec switching times and at first thought I got ripped off. Then, digging a bit:
Unisonic LMV331 (https://www.unisonic.com.tw/uploadfiles/836/part_no_pdf/LMV331.pdf) is 12usec :o
TI LMV331 (https://www.ti.com/lit/ds/symlink/lmv331.pdf) is 0.6usec, ST is 0.375usec, On-Semi 1.5usec
I complained to the vendor and they replied "we are just broker". Lesson learned.
I find Digi-Key uses their fine reputation to pimp for these unknown semi manufacturers, and the marketplace vendors as well. Not sure what loser MBA came up with this strategy.
It does piss me off, side loading disreputable vendors - for what exactly? They think they are a fulfillment center or something.