Author Topic: LM311P issue  (Read 486 times)

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Offline HendriXML

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LM311P issue
« on: August 28, 2019, 12:35:44 pm »
Hi!

For this little project, I'm using a LM311P bought from AliExpress (with the Texas Instruments logo on it, so it seems legit)
https://www.eevblog.com/forum/projects/nerfo-meter-measuring-the-speed-of-nerf-darts/msg2640588/#msg2640588

It is has a collector/emitter output. Because my circuit didn't function the way it should, I started debugging.

With the collector unconnected the emitter (pin 1) still sinks (11 mA) and sources (20 mA) current, when applying a square wave input. I measured mean dc amperage to either rail, so the max is higher.

I cannot explain this behavior and starting to think that it isn't a LM311P at all. (I tried several from the same ali order)

Doing the current measurement on the collector (pin 7) with an unconnected emitter I get 14 mA when sinking, and none when sourcing. But not following the input signal.

Any suggestions what could cause this?
« Last Edit: August 28, 2019, 01:50:05 pm by HendriXML »
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Offline magic

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Re: LM311P issue
« Reply #1 on: August 28, 2019, 04:18:30 pm »
(with the Texas Instruments logo on it, so it seems legit)
:-DD

TI is the favorite brand of counterfeiters to stamp onto jellybean parts. Post pics, oftentimes the shape of the package gives them away.
 

Offline David Hess

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Re: LM311P issue
« Reply #2 on: August 28, 2019, 07:01:05 pm »
With the collector unconnected the emitter (pin 1) still sinks (11 mA) and sources (20 mA) current, when applying a square wave input. I measured mean dc amperage to either rail, so the max is higher.

I cannot explain this behavior and starting to think that it isn't a LM311P at all. (I tried several from the same ali order)

The emitter output cannot sink current with the collector unconnected so the part is either damaged or not an LM311.

Quote
Any suggestions what could cause this?

Check the internal schematic of the LM311.

The LM311 is not designed to work with only one of the collector or emitter outputs connected.  If the collector is connected to a positive supply, then the emitter output can pull up.  If the emitter is connected to a negative supply, then the collector output can pull down.
 

Offline HendriXML

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Re: LM311P issue
« Reply #3 on: August 28, 2019, 09:55:20 pm »
Sometimes Chinees stuff makes me laugh. I one saw a toy figure of a Gorilla, it had quite a long tail. It was a good resemblance of the real thing. Except gorilla's don't have tails. So some guy in China made a pretty nice Gorilla from probably a photo which "hid" the non existing tail. But how did he determine the tail size, I wonder?

And what kind of creature is my LM311 in reality, I really wonder. I'm now certain I got something else. (An op amp or push pull comparator) Because my circuit (no rocket science) works with a LM211 just fine.

However even in my batch of LM211 I got a lot of fake ones! (They look the most pretty though)

I think I learned my lesson.
« Last Edit: August 28, 2019, 10:29:03 pm by HendriXML »
“I ‘d like to reincarnate as a dung beetle, ‘cause there’s nothing wrong with a shitty life, real misery comes from high expectations”
 

Offline ozcar

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Re: LM311P issue
« Reply #4 on: August 28, 2019, 11:17:38 pm »
I bought some LM311s about 9 months ago on Ebay.

When the package arrived from China, it was marked “Gift. Plastic patch, Total Value 0.02”. The contents looked OK, TI marking, but as LM311s they worked about as well as plastic patches.

I'm pretty sure that I then turned up an old thread here, from years ago(?) where somebody reported fake LM311s, which iirc they thought were likely some opamp. I can't find that thread now.

So what is it about LM311s? Somebody mislabelled millions of them and continues to flog them?
 

Offline HendriXML

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Re: LM311P issue
« Reply #5 on: August 28, 2019, 11:56:46 pm »
I did a check on what order they came from, it seems I ordered them twice. So I'll see whether even one store send good ones.

But it gets me thinking on how much more complete rubbish ic's I might have "on stock"  :palm:

Maybe together with the rusty diodes I received last time I can make some art thingy. And how about adding some """"""1%""""" resistors I'm sure they will add a finishing touch. 
“I ‘d like to reincarnate as a dung beetle, ‘cause there’s nothing wrong with a shitty life, real misery comes from high expectations”
 

Offline ozcar

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Re: LM311P issue
« Reply #6 on: August 29, 2019, 01:40:34 am »
I found the old thread:

https://www.eevblog.com/forum/chat/fake-andor-mislabelled-lm311-)/

Poster there said that they might be mislabelled LM358s. At the time I ran into the issue, I did a quick test on the supposed LM311s I had received, and it seemed plausible that they too were LM358s in disguise.

I wonder if yours are similar?
 

Offline T3sl4co1l

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Re: LM311P issue
« Reply #7 on: August 29, 2019, 02:28:30 am »
Flowchart for Discovering Counterfeit Components
1. Did you buy from eBay or Ali?
--> It's fake.

Assume this until you discover otherwise.  Doesn't matter if it's a 2N3904 or a brand-new Intel CPU.  They literally salvage floor sweepings, grind off the original part number, laser or print a new number and re-package them.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline David Hess

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Re: LM311P issue
« Reply #8 on: August 29, 2019, 04:54:42 am »
Assume this until you discover otherwise.  Doesn't matter if it's a 2N3904 or a brand-new Intel CPU.  They literally salvage floor sweepings, grind off the original part number, laser or print a new number and re-package them.

I was dubious about reports of counterfeit 2N3904s until I remembered that my last batches of TO-92 BC series transistors all performed poorly and tended to oscillate.  Hmm, I still have them and now have a 7CT1N curve tracer; I should check them.
 
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Offline magic

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Re: LM311P issue
« Reply #9 on: August 29, 2019, 07:13:16 am »
A short list of fake ICs I know exist:

PL2303 - Prolific doesn't sell those chips to retail distributors so rest assured all are fakes. Multiple different clone dies exist. IME they work OK, though :)
DS18B20 - I have seen two different clones, both don't meet accuracy specs, one is really bad even at room temperature. Beware of preassembled cables with those inside - you have no idea if they are genuine.
TL072 - multiple people reported fakes by now, it seems some kind of LM358 is inside because cheaper than JFET opamps.
NE5532 - you either get recycled chips of random vendors with NXP markings (NXP never made those chips, Philips did) or some apparently Chinese RC4558 clone with TI markings. Maybe the latter can be had with NXP markings too, dunno.
NE5534 - those at least can be had with Philips markings which tend to be actual Philips, but I have also seen "NXP". In both cases, recycled. One Philips even had a ripped-out via still soldered to its pin.
LM4562 - usually NE5532 inside.
Burr Brown parts - to the first approximation, all are fake :) Zeptobars has pics of TL051 sold as OPA2134 and some AD part as OPA627, I have a fake OPA2604, no idea what it really is but it doesn't meet the spec.

Also, watch out for transistors made by "second source" vendors like InChange Semiconductor Company (ISC) or SavantIC Semiconductor. In theory it sounds nice, it practice they are crap which barely meets "minimum" specs and isn't even rated for things like SOA at all.
Some sellers may lie and say they sell brand name transistors while actually sending those "replacements". And of course there is a whole market of transistors with false markings.

I generally advise to avoid anything from this list because once a counterfeit part is available, it drives real ones out of the market thanks to lower price.
 

Online Redeeman

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Re: LM311P issue
« Reply #10 on: October 17, 2019, 09:44:32 pm »
I found the old thread:

https://www.eevblog.com/forum/chat/fake-andor-mislabelled-lm311-)/

Poster there said that they might be mislabelled LM358s. At the time I ran into the issue, I did a quick test on the supposed LM311s I had received, and it seemed plausible that they too were LM358s in disguise.

I wonder if yours are similar?

i looked at both these fake lm311's and real lm358 on my rigol scope, they had identical response, im 99.9% sure they were lm358's.

I should note however, that I have bought many of these jellybean things on aliexpress and they have behaved as expected, whereas a large amount of those i've bought on ebay have been fakes of varying physical obviousness
 

Offline HendriXML

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Re: LM311P issue
« Reply #11 on: October 17, 2019, 11:38:07 pm »
After this lemon, I received 5 LM335Z temperature IC's which where instead some kind of transistor.

It's nice to have a bit of a stock, sourcing large quantities from reliable sources however can become expensive.

But I also know that if I exactly know/knew what I would need, buying only that from reliable sources would be cheaper.

But it still nice to have some stock for a quick experiment, however I'm more and more turning towards reliable sources. The packaging is better, the labelling is better, the specs are more valid. In a way that is worth some money too.

Trying to use fake components cost a lot of time to debug, that's what bothers me most.

« Last Edit: October 17, 2019, 11:55:10 pm by HendriXML »
“I ‘d like to reincarnate as a dung beetle, ‘cause there’s nothing wrong with a shitty life, real misery comes from high expectations”
 


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