Bogus parts from Reputable Dealer?

[Jwillis]

I don't want to mention the North American dealer just yet out of respect until I figure what might have gone wrong.
I bought 10 pieces of TLV2371IP as suggested for a parallel mosfet linear electronic load. My intention was to parallel 2 mosets with 2 TLV2371IP to control.I was simply wanted to test the circuit design and expand to 4 mosfets when things go correctly with 2 .  Seems simple enough right?
Now on the first try 1 of the op amps worked correctly, but I couldn't get the second one to work . It seems around 250mV  is leaking back from  pin 3  and the out puts is the same as the supply 9V on the one that wasn't working right .No voltage is applied to the number 3 pin . I changed  6 of them with similar results with slightly different voltage leakage into pin 3 . The one that worked continues to work. So figuring it may be a bread board issue. I re orientated the bad circuit but got the same results .So I changed out the bad one for another one . Same results .6 out of 10 got changed . Same results.   So I switched the two op amps in the two  circuits .Well the good op amp works as it should in the other circuit now  and bad op amp doesn't work where the good one used to be.     So its not the circuit . So I changed the "bad " again (# 7) and low and behold it worked . So I pulled it out to test the last one left out of the 10 and same results as before it won't work. 8 out of the 10  are uncontrollable .Ok so I have 2 out of 10 that work. Now I admit I'm not an expert on op amps but I was being really careful about static and making sure everything was hooked up right before power up. Both circuits are exactly the same Resistors are all 1% . Capacitors are new and measure fairly close.  Checked the mosfets and both are functioning .Both circuits receive a parallel voltage  at pin 3 . I tried to get the ones that don't work by adding an offset thinking that may be the problem but the offset with a 200k trim pot don't seem to do anything.i tried a voltage divider at pin 3 but that does'nt make any difference either. The voltage is at pin 3 is coming from the chip.
Now before I go and make a complete fool out of myself to the dealer I would like to test each failed op amp for leakage and functionality.I don't have really spectacular gear. So what would be the simplest way of doing that so I have evidence to show to the dealer in case they decide to get nasty about it. 

Now, from I understand when I supply the op amp with 9V  there should be  no voltage at the inverting and non inverting pins  and no voltage at the out put  relative to ground  correct ? When used in common mode I should only get a voltage at pin 6 when a voltage is applied to pin 3 ,correct?
I haven't had this sort of thing happen before with other op amps I've used and I'm out of ideas.

[nigelwright7557]

I would have thought a reputable dealer wouldn't buy rubbish.
I have bought IC's off ebay in the past and had bad experiences like you in that some worked and others didnt.

On a previous project I bought in some op amp's for RS (reputable dealer.)
The circuit behaved very strangely with impossible voltages on op amp pins.
Turned out my fast op amp was also bi polar and had quite a bit of input current which messed up my potential divider voltage.

Another problem I found with op amps is the bandwidth, which in reality is only small signal bandwidth.
If you have a large signal going in the bandwidth is much less.

[E-Design]

not at all likely "bogus" parts. Post your circuit.

[ebastler]

not at all likely "bogus" parts. Post your circuit.

Agree, and could you post a photo of the breadboard setup too please?
Something oscillating maybe?

[ArthurDent]

If you did get bogus parts from a major supply channel, this isn’t new. Twenty plus years ago I worked for an international company and we made some electronic test equipment for utilities and we had open parts orders from major parts suppliers.  All of a sudden almost all of this equipment we made was failing test and it was found that one shipment of a particular fairly expensive IC that we had been ordering for years from the same supplier was the problem. After an investigation it was found that all those ICs in this one shipment were relabeled crap. We never found out how this happened but the supplier certainly wouldn’t have done it knowingly and they made good on the repairs we had to make.

[Siwastaja]

Looking at your level of "documentation", it's most likely that there is something wrong in your circuit design.

Please post full schematics, photo of the layouts, and actual measurement results (like scope traces) in a readable way.

[rstofer]

It sometimes happens that known bad components, those that failed final test, make it into the supply stream by fraudulent schemes.  It's a real problem for the factories, not only do they have the losses associated with the failed components, they will double that loss when they make good on the failures.  They do everything in their power to prevent this from happening including smashing up TO-3 packages with a jackhammer.  After all, they still want to recover the gold.

I suppose a factory lot could bypass final test somehow.  It would be a screw-up but I guess it could happen.  The factory and their distributors will do everything in their power to make it right.  Their reputation as a manufacturer/supplier is riding on how they handle screw-ups.

It is highly unlikely that this is happening, post your circuit.

I'm not a big time hobbyist so I only place a few orders per year but I have never gotten a defective component from DigiKey or Mouser.  Could be luck, I suppose.

[wraper]

Now, from I understand when I supply the op amp with 9V  there should be  no voltage at the inverting and non inverting pins  and no voltage at the out put  relative to ground  correct

Nope. And output can be anything. No voltage related to what? And op-amps generally don't have "ground" which can be considered as reference point to begin with, consider it just as negative power supply. Often GND (V-) pin has negative voltage in reference to actual GND of circuit. And operation of inputs/output is referenced to actual GND and has nothing to do with voltage on power supply pins..

When used in common mode I should only get a voltage at pin 6 when a voltage is applied to pin 3 ,correct?

What you mean by common mode to begin with? If you leave even one of inputs floating or connect them together, output can be anything.

[ebastler]

No voltage is applied to the number 3 pin. [..]
Both circuits receive a parallel voltage  at pin 3. [..]

Now, from I understand when I supply the op amp with 9V  there should be  no voltage at the inverting and non inverting pins  and no voltage at the out put  relative to ground  correct ? When used in common mode I should only get a voltage at pin 6 when a voltage is applied to pin 3, correct?

As stated a couple of times above, we would really need to see a schematic. But in the meantime, I was trying to figure out what I can from the text.

The first two sentences in the (shortened) quote above seem contradictory. What did you connect to pin 3? And, reading further to the final paragraph -- did you leave pin 3 open, by any means? If so, that won't work!

Finally, a comment unrelated to content and technology: You would really do yourself and all readers a favor if you adopt the standard typographic convention of putting a space after punctuation marks, not before them.

EDIT: Ah, looks like wraper has the same suspicion and was quicker than me putting it in words...

[wraper]

Here is some info about unused op-amps. It can give you some clue what will happen when you don't connect inputs as for normal operation.

[jmelson]

I've have numerous cases where Mouse and DK sold me less, more, incorrect or damaged parts.

To be fair, that doesn't happen often. I make ~20 orders from each of them each year, and on average I have only one issue per year, so not a big deal.

At the end of the day, you are going to QC the parts. I presume they don't sell fake, so what I care are just broken, wrong P/N, less QTY or extra parts.

I buy mostly from Digi-Key, and also Mouser and Newark.  A long time ago, somebody at Digi-Key was stealing parts, and a BUNCH of cut tape orders were coming up short, like half what I ordered.  I guess their security people eventually figured out who was doing it and canned them.  Otherwise, I have had VERY few errors from any of the above.  I did get the wrong regulator once, it was supposed to be fixed 5 V, and I got the adjustable regulator version.  One other issue was for a time they were taking FPGAs out of the Xilinx tray and repacking them in little tiny cut tape strips of 5, which I then had to put back in trays to run in my P&P machine.  In all that handling, fragile leads could get bent a little.

I just reflexively do static-safe handling, grabbing the bench before touching any devices or boards, and keeping all sensitive parts in static-safe
packaging of some sort.  I almost NEVER have problems like you report.  I've probably built gear with 100K ICs over the last 40 years, and can
count on one hand the number of bad parts I have encountered when there was no reason (improperly connected power supply, wrong signal connection, part soldered on in wrong orientation, etc.)

I did have one incident when buying a bunch of Analog Devices op amps from a major NON-franchised distributor.  After mounting 25 of these chips on a board, half of them blew up.  AD had recently changed their marking/logo and put their triangle logo near the pin 5 side of the chip.  I suspect another assembler put bunches of chips in their P&P machine backwards, and assembled boards.  Then, after massive failures, they scrapped the boards, the chips were picked off and cleaned up, and re-reeled.  After talking with AD, I thought to ask, was it possible for a reel of ICs to have varying date codes?  They said that was ABSOLUTELY impossible in their process, and clearly indicated the parts were either counterfeit or salvaged.  So, I swore to NEVER, EVER, deal with that outfit again.

But, other than that, I have had great reliability when buying parts from the major, franchised distributors.  I know that in the past, Newark scrapped all returned merchandise, as ourt local surplus outfit bought it by the pallet load.  Some of it was bad, like power supplies, but most of it was fine and just "ordered the wrong part".  But, refusing to restock anything that has been opened should keep their stock pure of counterfeits and damaged parts.

So, I'm guessing you have caused static or electrical overstress damage in your experimenting.

Jon

[Jwillis]

The conceptual design was derived from other similar designs and https://www.richardsonrfpd.com/docs/rfpd/Microsemi%20How%20to%20Make%20Linear%20Mode%20Work.pdf

The TLV2371 op amp will operate with single supply and no voltages are exceeding maximums .Common-mode input voltage (VCM)   0 - VDDV http://www.ti.com/lit/ds/symlink/tlv2371.pdf

As I stated I'm not as experience as many others here and if I get some terms incorrect I apologize. But the individual circuits are  similar to other circuits described by many other people.The two circuits are identical.   Two of the 10 op amps purchased work correctly in my circuit where as the other 8 do not.
 If no voltage is applied to pin 3  there should be no voltage at pin 3 . The 2 working op amps confirm this. The 8 non working op amps have approximately  200mV at pin 3 with no voltage applied to pin 3. Ergo they must not be functioning correctly.

[wraper]

What is the meaning of "no voltage to mosfet"? If there is no voltage on the drain, feedback loop won't work at DC, thus opamp voltage should go up to the positive rail voltage if any positive voltage is present on non-inverting pin. Also I don't get about "This circuit works" on the left side of schematic. Does it work with all op-amps or not? Did you run right part of circuit with 2.2k resistor from inverting pin to GND disconnected?
EDIT: Also resistance of gate resistors is way too high.

[rstofer]

Where is the negative supply connection on the 2d op amp?  It is clearly shown on the op amp at the left and not shown at the op amp on the right.

[ebastler]

Thanks for the schematic, JWillis. Could you also post some photos to give us an idea of the layout and wiring?

Edit: I don’t see any decoupling caps for the op-amp supply, which reinforces my earlier suspicion that the op-amps may be prone to oscillations.

[Jwillis]

To add I've worked with several other op amps without complication in other projects . UA741CN , BA4558 AND 4559 , TL081CP , OPA445 .OPA604  to name only a few. I've also worked with many many other sensitive chips without complication.
I'm not the type to boast but I'm also not a complete moron when it comes to complying to safety matters concerning the ESD of these components.
The only time I have ever destroyed chips is when I applied to much voltage to the supply. I am learning so mishaps do occur and I do recognize where I go wrong .
If I seem upset you would be correct . I have bought hundreds of components form Ebay and Banggod  and other non recognized dealers across the world and have had non of them fail when used in the correct manner.
This is the second time from this  "reputable"  dealer that I have had premature failure of components. the TLV2371 and a Mosfet  FDL100N50F which failed at 5 Watts.10 V and 0.5 A.
I don't buy a lot from Digikey because of the method of shipping is not compatible to rural address. It's to much of a pain in the back side to deal with.
But when I get a 90% failure rate with Digikey and a near zero failure rate from other unofficial , non recognized dealers , I question the integrity of supposed  Authorized Distributors . 

[rstofer]

What is the meaning of "no voltage to mosfet"? If there is no voltage on the drain, feedback loop won't work at DC, thus opamp voltage should go up to the positive rail voltage if any positive voltage is present on non-inverting pin. Also I don't get about "This circuit works" on the left side of schematic. Does it work with all op-amps or not? Did you run right part of circuit with 2.2k resistor to GND disconnected?
EDIT: Also resistance of gate resistors is way too high.

I thought so too but these devices aren't being used as switches.  So, we're not interested in dumping a lot of charge per second into the gate.  I'd have to research that, I think.

Since there is no appreciable gate current, there is no reason not to reduce the gate resistor to 1K.  As long as the op amp doesn't latch up at startup, it should be fine.  In the linear mode it should be making small changes to gate voltage.

  In the meantime, I'm more interested in the right hand op amp negative supply and it appears that the 10k works ok on the left hand MOSFET.  Well, we don't really KNOW that it works for all corner conditions but it might.

[rstofer]

To add I've worked with several other op amps without complication in other projects . UA741CN , BA4558 AND 4559 , TL081CP , OPA445 .OPA604  to name only a few. I've also worked with many many other sensitive chips without complication.

Yes, but... What about the negative PS connection to the right hand op amp.  Your schematic shows it omitted and that just happens to be the circuit that fails.  You have consistent failures with one circuit and no failures with the other circuit and you want to dump it on the op amps.  It is something about that right hand circuit that is different than the left hand circuit.

[Jwillis]

Ah rats sorry I made a mistake drawing the schematic . I.m aware that my mind is defective sometimes .I put in the correct drawing .I'm really sorry for that .

[Jwillis]

What is the meaning of "no voltage to mosfet"? If there is no voltage on the drain, feedback loop won't work at DC, thus opamp voltage should go up to the positive rail voltage if any positive voltage is present on non-inverting pin. Also I don't get about "This circuit works" on the left side of schematic. Does it work with all op-amps or not? Did you run right part of circuit with 2.2k resistor to GND disconnected?
EDIT: Also resistance of gate resistors is way too high.

I thought so too but these devices aren't being used as switches.  So, we're not interested in dumping a lot of charge per second into the gate.  I'd have to research that, I think.

Since there is no appreciable gate current, there is no reason not to reduce the gate resistor to 1K.  As long as the op amp doesn't latch up at startup, it should be fine.  In the linear mode it should be making small changes to gate voltage.

  In the meantime, I'm more interested in the right hand op amp negative supply and it appears that the 10k works ok on the left hand MOSFET.  Well, we don't really KNOW that it works for all corner conditions but it might.

The voltage to the Mosfets come from the circuit to be tested by the electronic load . So to test  the the op amps working (Input Output)   no voltage or current is required to pass through the mosfets at this time. I simply want to get the op amps to respond to the control voltage . 2 of the 10 do respond correctly . The 9v supply ground is connected to the control board and is common to the mosfets as well . The control board works as it should with a single Mosfet. the point of the project is to expand the current capabilities by paralleling mosfets .

[wraper]

no voltage or current is required to pass through the mosfets at this time.

Unless there is some current through MOSFET, feedback loop does not work. So in absence of control signal output of opamp basically becomes determined by offset voltage of opamp inputs which is different for every particular IC.

I simply want to get the op amps to respond to the control voltage .

... with non working feedback loop. You want for incomplete circuit (disabled feedback loop) to work "properly", whatever it means in your opinion.

[wraper]

Connect inverting input to opamp output and watch how output voltage follows input voltage as on circuit below. Or simply short the 0.1 uF capacitor without disconnecting resistor from MOSFET source and connecting to the gate. It will do the same.

[Cerebus]

no voltage or current is required to pass through the mosfets at this time.

It is required if you want it to work. The whole purpose of this circuit is to try and reproduce the scaled control voltage (0-1.3V on your diagram) across the 0.21 ohm resistors by controlling the current through the mosfets. If you aren't supplying a source of current to the mosfets it cannot do that, all that will happen is that the op amp outputs will go into positive saturation (assuming you're supplying some non-zero value of control voltage).

Do you understand how this circuit works? Are you trying to modify someone else's design without a fundamental understanding of what's going on?

[TerminalJack505]

I've attached a screenshot of your circuit running in a simulator under the conditions that you have described--so far as I can tell.

The simulation results should be pretty similar to what you would see in the real world.  What is it you're are seeing that is different?

[Jwillis]

To add I've worked with several other op amps without complication in other projects . UA741CN , BA4558 AND 4559 , TL081CP , OPA445 .OPA604  to name only a few. I've also worked with many many other sensitive chips without complication.

Yes, but... What about the negative PS connection to the right hand op amp.  Your schematic shows it omitted and that just happens to be the circuit that fails.  You have consistent failures with one circuit and no failures with the other circuit and you want to dump it on the op amps.  It is something about that right hand circuit that is different than the left hand circuit.

My intention is not to be disruptive in anyway. But I suffer from chronic anxiety and panic attacks which cause me to make mistakes.
My apologies for posting an incorrect drawing . But I already stated that both circuits are identical and that when the good op amp was swapped from one circuit to the other it worked as expected . I missed drawing the ground on the one circuit but it does exist in the real circuit . I've re-posted the diagram as it is in the breadboard .
The OP is a description of the procedures I made to resolve the issue at hand .
 

no voltage or current is required to pass through the mosfets at this time.

It is required if you want it to work. The whole purpose of this circuit is to try and reproduce the scaled control voltage (0-1.3V on your diagram) across the 0.21 ohm resistors by controlling the current through the mosfets. If you aren't supplying a source of current to the mosfets it cannot do that, all that will happen is that the op amp outputs will go into positive saturation (assuming you're supplying some non-zero value of control voltage).

Do you understand how this circuit works? Are you trying to modify someone else's design without a fundamental understanding of what's going on?

The working circuit delivers a voltage from pin 6 to  the Mosfet  regardless whether theirs a voltage at the drain of the mosfet or not . it makes no difference . With the good op amps installed the whole project works when a voltage and current is supplied to the control board. The bad op amps lock the mosfets full on and can not be controlled.

The bad op amps deliver 9v continuously At pin 6 with 0 volts applied to pin 3 . With 0 volts applied to pin 3 on the bad chips there is still 250mV coming from pin 3.
Considering that when the good op amps are installed the whole project works as it should . So I think I have a pretty good idea of what I'm doing.