#1677
ฝัง
- เผยแพร่เมื่อ 3 ต.ค. 2024
- Episode 1677
Magical op-amps from china. can anyone identify this magic 'LM358'
testing TL072 that are LM358: • #1625 These opamps mus...
(repeating myself) same topic: • #1058 Slew rates of op...
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In 1970 I worked for analog devices as an engineering tech. Back then IC op amps were pretty much the LM709 or t41. If you wanted a realopamp you bought a brick that was built of discrete parts and potted in epoxy. They were maybe 1-1/4"square and had 7 pinns, The populated opamp was dropped into a potting shell and some epoxy was squited into hold it all in place.
If the competition came out with something a little faser than yours you just dropped a small ferrite bead over the output pin and that tiny bit of inductance would goose the response just enough that you might just beat him.. Thats just the way things were 53 years ago.
I LOVE these videos on various characteristics of op-amps. It's one thing to make a video explaining what the characteristics are on the datasheet to help make sense of datasheets. But to actually make videos about each individual characteristic, at least the relevant ones, like you've begun to do with these is just another level of awesome. I would love to see more videos about specific characteristics not just for op-amps but BJT/FETs and other components. Although I'm sure you have a long list of topics you already want to do, so I'm just throwing the idea out there. I don't want to tell you how to run your channel. Thanks for taking the time to make this and all of your other videos. I've learned so much more from them since I discovered them. Cheers!
Those laser etched lm358 are golden you definitely found a rare and lucky chip and i agree it he fun to figure out what chip it actually is to get more as wow the trace it had was immaculate 😍
Time to decap the magic LM358 imposter and take a look at the die
Amazing. The only thing left would be to send one of the marvelous fakes to a semiconductor lab to decapsulate them and inspect the die to see if it is a chinese mix of copied designs or it is already a full copy of a known op-amp.
Hey Imsai guy, we have the tools at work to take the die out of the plastic package the manufacturer usually writes the part number on the die. We do this to check that we do not use fake parts in our instruments :)
If you send me one I will do this for you, then you would know the part number ?
send me an email, in the about page on my channel
Ordering parts from Ali is like a box of chocolates...
To bring up the contrast of the laser etching a smear of heatsink grease works really well. Thanks for your videos, always an inspiration often in ways I did not expect.
Overshoot in faster amps is very dependent on the circuit configuration and gain. A unity gain inverting amp will have different overshoot than a unity gain non-inverting amp. Increasing the gain to even 2 will typically reduce the overshoot. This is because frequency compensation in fast amps is a compromise. Those internal capacitors are not for slew rate control, as such, but for frequency compensation to make the amplifier stable. Some high frequency amplifiers are "undercompensated" and not stable at low gains. It varies, but the lowest stable gain is often around 5.
None of the amps tested qualify as "super fast" or anything even remotely close. High bandwidth amps with high slew rate would perform very badly on that crude test board.
Using a fast amplifier where you don't really need one can be fine if all you need is some gain for a signal. As soon as you put one inside a larger closed loop you better know what you are doing or you're begging for trouble.
Good points.
Slew rate is defined by the parasitic capacitances and the current flowing through the differential pair and the voltage amplification stage. The purpose of the compensation cap is to bring gain to unity before the frequency at which phase shift approaches 180 degrees and turns an amplifier into an oscillator. The reason the legendary NE5532 is (relatively) fast and low-noise is due to a clever way of split-pole compensation - and quite significant power consumption.
The last, unknown opamp looks really interesting.
More generally, noise gain controls the bandwidth. You can have 10x noise gain and 1x voltage gain - and voila, slower and more docile circuit. Noisier though :)
Hello and thanks again for the video. You could rename this video to include the word "damping". The op amps that ring are under damped, that great one is critically damped and the slower ones are under damped. I'll have to go through my collection of OP amps. I do have lots of parts I purchased from China.
Honestly I've managed to de-encapsulate a ton of chips and transistors by holding them in some tweezers and cooking them with a lighter then squeezing them til they pop apart with pliers.
Once apart the die is usually stuck to one face (always the non etched side visible of course.....) so I cook it again with flame and lightly flick the die out with tiny tweezers. Boom.
Throw it under a microscope and check er out. If you're lucky they're etched with the actual part number. I've done this probably 100s of times. But always have extras to try again lol.
Once you go on the Grey market there's no knowing what you'll be getting, even the licensed versions can be modified by cost-down ie. lets remove some higher functions by removing a few die components. We were almost caught out by this a few times when someone decided not to use verified vendors. so yeh, buyer beware...🧐
Do you have any LM351 op amps to check it against? LM351's have an 16V/uS slew rate. I used these in the mid-1970's when I needed a high slew rate op amp.
NE5532 is popular because it's cheap and relatively low-noise, 5 nV / sqrt(Hz). Step response is not that important when it comes to frequencies below 20 kHz.
High slew rate and wide bandwidth are very important in audio applications. While the Nyquist frequency may not be higher than 20kHz, you still need high feedback factor well into hundreds of kHz in order to suppress higher order harmonics. That's why LM358 with its open-loop gain roll-off at 10kHz is terrible for audio. It's so slow that it can't even cancel the crossover distortion caused by its class C output.
Really nice information, clear presentation. Thanks!
love this kind of thing btw.
Yeah, me too !
You are the most clueless.
See, never buy 3. Get 20+ !
So apparently any part can be a counterfeit, and i was so proud of my small op amp collection.
It looks like it's a case of suck it and see I'm afraid. I've built up quite a reasonable collection too and now I'm going to need to check them all.
Damn it! I was thinking about the same thing. Time to dust the Oscilloscope off.
Do you know who's making those fake chips? Are they ordered by one of the major semiconductor companies, or are they being produced inside China?
I've always understood that the fakes are simply the rejects from the production line, the Chinese simply recycle them back into the supply chain to our old friends aliexpress ect, Clive Sinclair built his first fortune on dodgy MAT100's that were afik destined for landfill, I'm open to correction!.
As the data sheet often shows the (simplified) internal structure, you have certain common groupings - bipolar / FET, NPN / PNP front end etc. The LM324 & LM358 are easily detectable by externally measuring the input common mode range. Further you can check the bias current polarity. Old designs had common mode voltages limited at both low side and high side well below the power rails. Then you started seeing some with common mode reaching either negative or positive rail. Finally you now can find "rail-to-rail" designs, although most of them are limited in their power supply ratings to something like 5 or 7 V. You could try to determine the original part from a few more comparisons on these additional features, especially if you have more samples (as you seem to have).
that funny part, proves the superior quality AO, is not exactly superior quality. bigger slew rate, maybe any producer can do, trading for instability. those very fast AO, are not really superior, they are just less stable
It would be interesting to see the characteristics op07
th-cam.com/video/cOC9aj_jtwo/w-d-xo.htmlsi=TLQ1nqlKNpH0Zu4t
looking at TLC271 with its programmable bias mode low/high/medium ?
Do all the Chinese LM358s you have on hand have the same fast clean slew rate? Last cool op-amp I was playing with is the LME49723. Also the OPA1611.
I shall check that out as my current 'poster girl' opamp is the OPA1656 !
Hi!!do you know any site or forum where they discuss the design of an operational amplifier?
th-cam.com/video/Z8JDsvfZjL8/w-d-xo.htmlsi=EeMnl_a1D0oqxdwM
@@IMSAIGuy thank you!! Is there also a MOSFET version? I am particularly interested in polarization via MOSFETs
www.designinganalogchips.com/_count/designinganalogchips.pdf
Pry it apart and look at it under a microscope. There should be markings on the die
So why does your box get labeled Tuvalu? Did you work Tuvalu and get op amps as your QSL? Cool if that was the way it works. DX with prizes, and I want in.
th-cam.com/video/OJaooiIIlas/w-d-xo.htmlsi=QSgUES5XnWICXUNa
Love this sort of thing....cheers!
Sir do you have tsl237 sensor?
similar: th-cam.com/video/Gmkevf-RNr8/w-d-xo.htmlsi=saInb0IBIT3D5AqC
LF353 marked as LM358?
The LF353 datasheet lists a typical slew rate of 13V/uS. The mystery opamp seems somewhat faster than that. I'd like to see how it behaves at crossover. I like it when they specify slew rate per second, 13MV/S sounds much more impressive. ;)
*13V/µs Fast op amp?*
Try 2500V/µs - ADA4870 (Real beast 1A, 40V)
I want to make a Amp for my Waveform Generator with it :)
Try THS3491, a lot better BW, but all that does not mean any of them are a good fit.
OpAmps are always about compromises and balance.
that LM358 is Chinese