EEVblog #600 - Opamps Explained - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: April 05, 2014, 11:51:24 pm
content: The most often requested video! Dave explains what Operational Amplifiers (OpAmps) are and how they work. The concepts of negative feedback, open loop gain, virtual grounds and opamp action. The comparator, the buffer, the inverting and non-inverting amplifiers, the differential amplifier, and the integrator circuit configurations are also explained.Then a practical breadboard circuit to demonstrate a virtual ground and the effect of voltage rail limitations.All EEVblog Opamp related videos are here:https://www.youtube.com/playlist?list=PLvOlSehNtuHu2FviAaZaiyXwN41G4b1Lf

author: w2aew
author_rank: Super Contributor
timestamp: April 06, 2014, 12:36:58 am
content: This is going to be one of your most popular ones Dave. My video that discusses "how to understand most op amp circuits" is far and away the most viewed one on my YouTube channel. Let's see how many hours it takes for #600 to surpass the view count on mine!

author: c4757p
author_rank: Super Contributor
timestamp: April 06, 2014, 01:02:24 am
content: You must have stopped about a quarter of the way through, subolg123, as he pointed out that it was just an approximation.Idowish he elaborated on the comparator bit though. Some op amps have diodes between the inputs and can be destroyed by a large input differential...

author: dentaku
author_rank: Frequent Contributor
timestamp: April 06, 2014, 01:29:58 am
content: Great stuff. When looking at the inverting amplifier circuit I wondered how it worked.Am I correct in saying it's because current can actually flow INTO the output? I didn't realise that.I can't see where else it would go.

author: c4757p
author_rank: Super Contributor
timestamp: April 06, 2014, 01:36:59 am
content: Quote from: dentaku on April 06, 2014, 01:29:58 amYes, the output can both source and sink.

author: Macci
author_rank: Newbie
timestamp: April 06, 2014, 02:34:06 am
content: I keep scratching my head at that last-minute problem Dave left us with.All I noticed is that those weird "virtual ground" oscillations happen when the input signal is more-less 0V, and they are about 500mV.Moreover, lower resistor values mean more current runnig through them. Perhaps the output saturates at some point and can't take in any more current?Or there is some current that all of a sudden flows in reverse, from output to signal input, thus forcing the "artificial ground" to jump for a moment?And bigger resistors simply make that current too small for this to happen? I don't know, but i want to know!

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2014, 02:53:09 am
content: Quote from: w2aew on April 06, 2014, 12:36:58 amIt won't have a patch on my soldering videos though.Within 10min of it uploading it was already on the first page search results for "opamps", so that helps greatly. It's all about the magical "google foo".

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2014, 02:59:31 am
content: Quote from: subolg123 on April 06, 2014, 12:44:57 amI think it's an important aspect to realise, so that's why I mentioned it. I did say they made bad comparators. They are actually ok for some circumstances. I used one in my uCurrent test jigs for example. So I really don't see the problem mentioning it, as you may very well see then used as crude comparators in circuits. So I think failing to mention it is actually worse than mentioning it.If you disagree of course, that's fine, but that's not the way I see it.QuoteI mentioned we were dealing with an ideal opamp, and that in practice it's not zero, and I have done other videos in input bias currents, and said I might do another video on the practical limitations.I can't haveeverythingin one video.Thinking of opamps as ideal opamps for the purposes of teaching is a very common and well accepted way to do it.Do you start out by teaching that resistors are noise devices?

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2014, 03:02:27 am
content: Quote from: dentaku on April 06, 2014, 01:29:58 amYes, they are totem pole outputs, they can both source and sink current (I thought I mentioned that somewhere?). As you said, there is no where else the current can go.

author: codeboy2k
author_rank: Super Contributor
timestamp: April 06, 2014, 03:07:16 am
content: Quote from: Macci on April 06, 2014, 02:34:06 amI know the answer.. but that's because I've been using opamps for over 25 years already.. so I'll leave it for the young players to figure it out

author: Macci
author_rank: Newbie
timestamp: April 06, 2014, 03:12:42 am
content: I just started electronics as a hobby/career 2 years ago, and I knew most of the stuff Dave put in this video, but nothing beats real-life experience I guess.Still looking forward to solving this. Am I even close?

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2014, 03:49:40 am
content: Quote from: subolg123 on April 06, 2014, 03:42:02 amAnd of course that's precisely who the intended audience is, no one else. Of course those more experienced with find countless practical holes in any such basic explanation.But beginners have to start somewhere, and bamboozling them all sorts of conflicting practical limitations in a basics video is just going to scare them away from electronics.

author: Jianan Li
author_rank: Newbie
timestamp: April 06, 2014, 05:18:15 am
content: So what was going on in the last circuit with the 1k and 10k resistor? I noticed something similar when I was playing with a different op-amp from TI the other day, and the resistors I used were 1k and 5.1k.

author: Kirigozo
author_rank: Contributor
timestamp: April 06, 2014, 05:25:12 am
content: Dave,Is there any chance you'll make the videos available for download from a server a bit better than a 286 on a dial-up modem? Download times that exceed 45 min regularly fail and have to be restarted. Some of us pay for internet access and wasting it is not an option.How about it?

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2014, 05:59:14 am
content: Quote from: Kirigozo on April 06, 2014, 05:25:12 amUnfortunately bandwidth to do this is ridiculously expensive.Before anyone jumps in and shouts Amazon S3 or something similar, no, it won't work, go and do the math using real numbers for video files.Sorry, this is one of those problems that has no easy solution. Just enough people (a few thousand) want to down the podcast videos to make almost any solution slow or really expensive (take your pick), but too few for me to justify spending the crazy amount of money required to make as fast as people expect.I have in fact considered simply dropping the podcast files altogether.

author: jadew
author_rank: Frequent Contributor
timestamp: April 06, 2014, 06:59:50 am
content: My first guess for the little spikes there is that they're caused by the input capacitance since they happen when the polarity changes.

author: vlad777
author_rank: Frequent Contributor
timestamp: April 06, 2014, 07:36:40 am
content: I suspect that totem pole (push pull) output goes to high(er) impedance near zero volts, and that is whyyou need less current through your feedback.

author: vlad777
author_rank: Frequent Contributor
timestamp: April 06, 2014, 07:40:27 am
content: At virtual ground, voltage signal has vanished but current did not.You can have a node at zero volts but still current flowing through it.Just imagine the ground rail of a power supply, it is at zero volts butthere is a lot of current flowing through it.

author: miguelvp
author_rank: Super Contributor
timestamp: April 06, 2014, 07:53:56 am
content: Quote from: EEVblog on April 06, 2014, 05:59:14 amJust sayinghostmonster.comused them for many years but my sites where not as popular as yours. They do claim no bandwidth limit as long as it's content to your site.Encode the videos with Quicktime Pro Hinted (even the PC version does a good job and that's what I used to use) and they actually stream at a good rate and compress very well for downloads as well.

author: BravoV
author_rank: Super Contributor
timestamp: April 06, 2014, 07:57:07 am
content: Quote from: EEVblog on April 06, 2014, 03:49:40 amThis, Dave is hitting the nail on the head on this part.Its like when we're at school in early days when we're just starting to learn how to calculate a circle's area or circumference but was hammered heavily on how the Pi was derived from with all those calculus or advanced math.Remember kids, this is where the Pi is came from ....Now .. calculate this 1st before we proceed with the calculation of the circle's circumference.As an electronics enthusiast, I'm one of those that was trapped & scared with those so called "technically correct" limitations that confused the hell out of me when I was learning op-amp at the beginning, and it consumed & wasted a lot of my productive hours.

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2014, 08:05:24 am
content: Quote from: miguelvp on April 06, 2014, 07:53:56 amIamusing Hostmonster for those files.The problem is simply one of bandwidth. You have a few thousand people wanting to download the file at once, no single server is going handle that kind of streaming traffic. You need a massive CDN.We had the same issue with the Amp Hour show. But we were able to use LibSyn at an affordable price. The video podcast is 10 times the file size on average, and at least double the frequency of episodes.And before any says Torrents, I've tried it, hardly anyone used it.QuoteI already use Handbrake with a high RF value, there is only so much magic you can do. And that's at 640x360, imagine if I did a higher res.

author: andtfoot
author_rank: Unknown
timestamp: April 06, 2014, 08:26:10 am
content: Quote from: Kirigozo on April 06, 2014, 05:25:12 amIs there something wrong with just using JDownloader to download the videos directly from youtube?

author: Kirigozo
author_rank: Contributor
timestamp: April 06, 2014, 08:27:11 am
content: Quote from: EEVblog on April 06, 2014, 05:59:14 amThanks Dave,I'll try again tomorrow. Might be a bit quieter.

author: zimzom
author_rank: Regular Contributor
timestamp: April 06, 2014, 09:01:50 am
content: I figure this is going to be a very popular video, just a slow burner. Lots of guys are looking for quality beginner info presented in English.I thought it was great, hope there are more in the series - but understand there are more views on the other types of videos so can understand why you don't do them so often.

author: ali80
author_rank: Contributor
timestamp: April 06, 2014, 09:30:46 am
content: Hi, is the last minute event caused by transition between output transistor pairs? If so, I guess adding a constant current load on the output would fix the problem

author: ultranalog
author_rank: Contributor
timestamp: April 06, 2014, 09:59:47 am
content: Great video which I'd love to remcomend to friends, but just have one niggle about your inverting amplifier. You are writing Av=Rf/R1 which is true from a magnitude point of view, but for beginners very confusing since you leave out the minus sign.Av =-Rf/R1makes more sense here. Those drawing a Bode diagram can work out for themselves that in the magnitude plot the minus sign drops out.

author: andtfoot
author_rank: Unknown
timestamp: April 06, 2014, 10:03:56 am
content: Quote from: ultranalog on April 06, 2014, 09:59:47 amThis is noted at about 31:30 into the video.Thanks Dave for the nice refresher video. It's been a while since I have looked at inverting opamp circuits, and the 'ah hah' moment of remembering for me was when Ohm's Law was applied to the first resistor.

author: dentaku
author_rank: Frequent Contributor
timestamp: April 06, 2014, 10:31:57 am
content: Quote from: andtfoot on April 06, 2014, 08:26:10 amYeah, People should be able to download he video through something likehttp://offliberty.com/It works very well.

author: opa627bm
author_rank: Regular Contributor
timestamp: April 06, 2014, 10:32:27 am
content: Quote from: EEVblog on April 06, 2014, 05:59:14 amUse torrent bro!

author: HighVoltage
author_rank: Super Contributor
timestamp: April 06, 2014, 10:47:39 am
content: It is very easy to download any youtube video with internet download manager (IDM)And if the connection breaks, it will continue where you stopped.Thanks for another great video

author: filip_cro
author_rank: Regular Contributor
timestamp: April 06, 2014, 11:45:46 am
content: Can you make video on how are op-amps build?I have basic knowledge but I want much more.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 06, 2014, 11:55:48 am
content: Quote from: EEVblog on April 06, 2014, 02:59:31 amIt would at least have been useful to say why they make bad comparators...

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2014, 12:16:08 pm
content: Quote from: mikeselectricstuff on April 06, 2014, 11:55:48 amSure, and it also would have been useful to say a lot of other stuff I didn't. Like I said, I can't cover everything in one video, it was long enough already.

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2014, 12:19:15 pm
content: Quote from: filip_cro on April 06, 2014, 11:45:46 amThere are many different topologies of opamp design, almost too may to count let alone describe I think. Ultimately though I don't think it is of major importance. Practicalities of using various types opamps is much more important to know than exactly how they are designed internally I think.

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2014, 12:20:51 pm
content: Quote from: opa627bm on April 06, 2014, 10:32:27 amI did, hardly anyone used it.

author: R_G_B_
author_rank: Frequent Contributor
timestamp: April 06, 2014, 12:31:01 pm
content: Dave,How do you make an operation amplifier operating as an intergrator stable at D.C low frequency?How do you stabilize cascaded opamp intergrators at low frequency e.g stop the scope trace from wondering and oscillating.even with feed back compensation I can not seem to get them to stabilize at frequencies below 30hz?Thanks

author: Christe4nM
author_rank: Unknown
timestamp: April 06, 2014, 01:04:25 pm
content: Even though most of the content of this FF was known to me that last question got me to think. In my very first course on electronics we used the LM358 and found that there was a discontinuity in the negative swing of the output. We found that the TL072 didn't have that 'feature' so we used that instead.Since I actually didn't know what causes this glitch, even though I had some ideas after Dave's video, I went to investigate. So I bread-boarded Dave's little circuit, put 2Vpp into the input and sure enough there it was, even with the 10k / 100k resistors. (lm358_1.png and lm358_2.png). With the 1k / 10k configuration it is present again, but at a different voltage (lm358_3.png and lm358_4.png).My first guess was that the glitch has something to do with the output current that the opamps needs to supply. With the 10k/100k configuration this should be about 0.2 mApp. With the 1k / 100k configuration this should be about 2 mApp. Hmm, a first quick glance at the datasheet for Output Current doesn't show a problem yet. The opamp should be perfectly capable of sourcing or sinking 2 mApp / 1mApeak.Now in the 1k / 10k configuration the glitch sits at about -600mV... Heh! That is a familiar voltage, could it have anything to do with the transistors in the output stage? Let's see where the glitch is in the 10k /100k configuration. Hey, that is about -6.6 V. About 10x (11 actually) as large. That looks to me as if there is indeed something going on with voltage/current and the output stage.The screen capture in lm358_1 also shows that the glitch is at a slightly different voltage for the negative going swing and the positive going swing. The Datasheet shows the internal schematic output stage. There you can see that there is a small resistor between the top BJT and the bottom BJT. I take it that is used for current limiting. (~0.6 V over the resistor turns on the BJT directly to the left.). Now I also know that a NPN and a PNP of the same 'family' can differ in capabilities. This is seen in the datasheet as that maximum output sourcing current is larger than the maximum output sink current.All in all my best guess is that the glitch has everything to do with the configuration of the output. I guess that when the input is at 0V the top BJT (darlington) in the output stage is still driving a bit of current through the current limiting resistor. Then, when the input goes positive (thus the output negative) the current going into the output actually goes into the top BJT's before the bottom PNP is turned on. So the output goes negative to about -600mV before the PNP really takes over from the NPN. In the 10k / 100k configuration this is only at -6.6 volts since the current through the current limiting resistor is 10x as small.Well that's my 2 cents. Hopefully I'm thinking in the right direction.Attached screen captures:Ch3: Blue trace: input signal, 1kHz sine, 2VppCH1: Yellow trace: output from LM358Both: AC coupled, Bandwith limit on, 1M input impedance, normal acquisition mode (not in High Res!)1) 10k/100k config.2) 10k/100k config.3) 1k / 10k config.4) 1k / 10k config.edit: added info about screen captures

author: nuhamind2
author_rank: Regular Contributor
timestamp: April 06, 2014, 02:20:20 pm
content: My bet is that some parasitic capacitance play a bit of role in here. My intuition tell me that any imperfection in open loop characteristic is - to some extent- repaired by the feedback path.

author: c4757p
author_rank: Super Contributor
timestamp: April 06, 2014, 02:27:04 pm
content: Hint: It's not due to capacitance!

author: arcover1024
author_rank: Newbie
timestamp: April 06, 2014, 02:36:39 pm
content: Maybe due to the input bias current. If this is the cause, the spikes should vanish if the non-inverting input was connected to ground through a resistor.

author: max_torque
author_rank: Super Contributor
timestamp: April 06, 2014, 04:00:39 pm
content: Eagle eyed viewers should also have noted the non linear effects due to the recovery from saturation during the segment where Dave reduced the rail voltage, which of course are present when an op amp is used as a comparitor (ie, fully saturated except during the transient output change/swing)

author: nuhamind2
author_rank: Regular Contributor
timestamp: April 06, 2014, 04:07:32 pm
content: Quote from: subolg123 on April 06, 2014, 03:31:39 pmSo,that's basically making the bottom transistor never conducting and eliminate crossover (it never cross actually). Basically making it a single supply.It seem that the opamp actually care about it's power supply,my whole life is a lie.

author: robrenz
author_rank: Super Contributor
timestamp: April 06, 2014, 04:09:09 pm
content: Excellent video Dave. You have a great knack for getting concepts across.

author: Mavro
author_rank: Contributor
timestamp: April 06, 2014, 04:11:53 pm
content: Great video Dave!It would be great to do a video on how opamps in audio circuits work. Audiophiles are always swapping out or in search of the best OpAmp. How does an OpAmp help in that situation?

author: hikariuk
author_rank: Unknown
timestamp: April 06, 2014, 04:25:44 pm
content: Quote from: EEVblog on April 06, 2014, 05:59:14 amThere's a Tampermonkey script that lets you download videos (amongst other functionality changes) directly from YouTube, if you're using Chrome. I shall leave the discussion of the ethics of such a thing to other people

author: Legion
author_rank: Frequent Contributor
timestamp: April 06, 2014, 04:46:42 pm
content: Just wanted to say thanks for the great video! I just started reading about opamps a few days ago so it was fantastic to have this video go up. I like that you didn't overburden the fundamentals with myriad small details. Kept the core concepts clear and easy to understand. I look forward to future videos on opamps.Thanks again!

author: Christe4nM
author_rank: Unknown
timestamp: April 06, 2014, 06:37:34 pm
content: Quote from: subolg123 on April 06, 2014, 03:31:39 pmGood find. So...Crossover distortion. Two words saying exactly what I guessed.Nice to read the reasons behind it though.

author: David Hess
author_rank: Super Contributor
timestamp: April 06, 2014, 10:16:58 pm
content: Quote from: R_G_B_ on April 06, 2014, 12:31:01 pmEither limit the DC gain or do some type of periodic calibration for the offset voltage and bias current.QuoteAdjust the feedback so the gain is less than 1 before the phase reaches 180 degrees. 135 degrees is typical. Learn to use a bode plot.

author: tom66
author_rank: Super Contributor
timestamp: April 07, 2014, 12:19:10 am
content: Audiophiles will use undefined terms such as "colour", "brightness", "danceable", "sonic redemption", "space clarity", "well-tempered personality" etc. to describe components.The terms can mean nearly anything.Fun fact: simply moving a couple of inches in your seat isenough to disrupt any audio comparisondue to the "comb effect". So it's very hard to accurately compare any audio system. A well designed amplifier will do nothing audible to the signal; the rest is up to the listener, and often the headphones or speakers, which introduce tons more distortion than any electronic part does.

author: Rutger
author_rank: Regular Contributor
timestamp: April 07, 2014, 12:40:34 am
content: Thanks for the video Dave, it was informative and short enough. I am glad you didn't go into all the detail explanations on why this and that, it would have made the video too long.My question; what is the most versatile jelly bean op-amp a hobbyists should have in his/her toolkit?

author: w2aew
author_rank: Super Contributor
timestamp: April 07, 2014, 12:45:16 am
content: Very glad to see Dave's video on this topic, and even happier to see that he used the same basic approach and examples in his video as I did in my video on the same topic. Of course, I didn't go into the same level of detail in my 14 minute video. This video has been the most-viewed video on my channel for a while, so I'm sure that Dave's is going to surpass mine in total views very shortly.Here's my video from about a year ago:

author: Legion
author_rank: Frequent Contributor
timestamp: April 07, 2014, 02:25:50 am
content: Quote from: w2aew on April 07, 2014, 12:45:16 amThanks for the video. I enjoyed it. U ar uh gud teechur n enjinere!

author: Pasky
author_rank: Regular Contributor
timestamp: April 07, 2014, 03:30:10 am
content: This is probably one of my favorite videos to date now, I learned a lot watching this one, thanks a lot.

author: hikariuk
author_rank: Unknown
timestamp: April 07, 2014, 03:53:59 am
content: Quote from: tom66 on April 07, 2014, 12:19:10 amWhich is kind of amusing because "well-tempered" actually means something in music: it's a type of tuning.

author: sergey
author_rank: Regular Contributor
timestamp: April 07, 2014, 06:32:24 am
content: Great video, Dave!And yes, thumbs up for the proper opamp termination video

author: sergey
author_rank: Regular Contributor
timestamp: April 07, 2014, 09:20:48 am
content: Quote from: subolg123 on April 07, 2014, 03:37:19 amThat's really great reading, thanks for sharing the paper with us!

author: Frink42
author_rank: Newbie
timestamp: April 07, 2014, 10:46:34 am
content: Quote from: tom66 on April 07, 2014, 12:19:10 amAudiophiles simply aren't consistent with what they want/mean. A perfectly designed amplifier using an op-amp will sound "cold" and probably "harsh" even though it doesn't distort at all. Then, they will use a valve amp "because it sounds better", when all it really does is adding distortion heh. All in all, sound quality is subjective.It would be fun to know which kind of distortion is percieved as "good".

author: mrflibble
author_rank: Super Contributor
timestamp: April 07, 2014, 10:55:16 am
content: Quote from: subolg123 on April 07, 2014, 03:37:19 amAnd when that dropbox url goes poof, you can still download it from AD:http://www.analog.com/library/analogdialogue/archives/39-05/web_chh_final.pdf

author: Rutger
author_rank: Regular Contributor
timestamp: April 07, 2014, 07:36:40 pm
content: What is the most versatile jelly bean op-amp a hobbyists should have in his/her toolkit?

author: vieirae
author_rank: Newbie
timestamp: April 07, 2014, 07:44:15 pm
content: Hi DaveGreat video on OpAmps!Would it be possible to explain the functionning of Norton current-based OpAmps. When would the use ofsuch devices make sense (current regulation instead of voltage)? Or is it always better to regulate currentby regulating voltage over a resistor using a "classical" OpAmp?

author: David Hess
author_rank: Super Contributor
timestamp: April 07, 2014, 08:19:40 pm
content: Quote from: Rutger on April 07, 2014, 07:36:40 pmIf I count cost than probably the 324/358 but my personal preference is for low input current bipolar operational amplifiers like the LT1008, LT1012, or LT1097 which support external compensation or overcompensation. If I needed single supply operation, then the LT1006 would be my choice.

author: calin
author_rank: Regular Contributor
timestamp: April 08, 2014, 03:53:48 am
content: That is exactly what hapenned to me few weeks ago .. the damn step occurring at zero crossing... that same exact note got me out of it. Go figure ... "[size=78%]The LM358 will operate satisfactorily in balanced supply operation so long as a load is maintained fromoutput to the negative supply." Perfect case of headbanging for electronics morons like meat leas t I am good enough @ googelingQuote from: subolg123 on April 06, 2014, 03:31:39 pm

author: David Hess
author_rank: Super Contributor
timestamp: April 08, 2014, 04:20:09 am
content: Quote from: calin on April 08, 2014, 03:53:48 amThe improved LM358/LM324 operational amplifiers like the LT1013/LT1014 have class AB output stages so do not suffer from that particular problem.

author: sportq
author_rank: Regular Contributor
timestamp: April 08, 2014, 08:11:21 am
content: Quote from: subolg123 on April 06, 2014, 12:44:57 amIt seems ok for HP/Agilent/Keysight, this is from page 129 of the E3631A schematic (a current product). U6 is an OP27 used as a comparator.Pete

author: mexakin
author_rank: Contributor
timestamp: April 08, 2014, 12:04:50 pm
content: Hello,i do really like those fundamentals about OpAmp and everythign surrounding it, since practical issues you cannot learn from a textbook but need experience or listen to someone who got expirience. I did not yet watch this episode. But just want to contribute, since I am into doing analog digital design since 4 years now, and I did read and build a whole lot sensors, mostly transimpedance stuff, where inbut bias currents hit you pretty well, due to the huge gain you have to achieve, but anyway, what I did want to recommend for those who wanna learn more about OpAmps and their history:I did read Bo Lijeks: Semiconductor History, pretty nice book also packed with a lot of anecdotes and stories not so much about Opamps but semicondurctor in general ( it has a whole chapter on Bob Widlar as well, which befor I didnt even notice, and I did study electronics enigneering so I guess probably less than 20% of all student know him after their diploma , which is kind of sad since he and his surround works really puts some life into some rather dusty studies)The AnalogDevice *pfd is really readable as well, but what really did strike me is Hans Cammenzids little book about analog chips, for those who didnt know ( as myself) he is the inventor of the 555-Timer ( which Dave also did a episode about some month ago) and his book is really awesome to read, it explains everything in a very down to earth approach, its not packed with formula but with hands on data, so dont expect to really learn how, but rather understand why the OpAmp and semiconductors evolution took place and why we got OpAmps and their internal structure right now. Adn this is also explained in semiconductor levels , liek why is it important to not design big resitance in semiconductor material and so on, and on.http://www.designinganalogchips.com/The book should be available free to download, his other book about the history of electron is also really interesting, I did read it as I read a lot bibliographies about guys involved with electrons, I like it to see how things evolve and those books pretty much do it.And the last source is Analog circuit design by Jim Williams, it is a collection of big analog designers telling a lot of different stories about their life their thoughts about design, some talk about OpAmps, others about who to become an analoge designer, I think even Philbrick tells the story about his first OpAmp.http://books.google.de/books?id=CFoEAP2lwLEC&pg=PR4&lpg=PR4&dq=ISBN+0-7506-9+166-2&source=bl&ots=4rnvpNfd1i&sig=KcS9lnSrBpleKfAYsaEKns528co&hl=de&sa=X&ei=IOVDU4-bBIjRsgbu64D4CQ&ved=0CDAQ6AEwAA#v=onepage&q=ISBN%200-7506-9%20166-2&f=falseISBN 0-7506-9 166-2because I dont know if the link works, and there are quite some books with the same title but different content.So thats it, i hope someone will be interested in any of this.Have a nice week.

author: pgross
author_rank: Contributor
timestamp: April 08, 2014, 01:47:54 pm
content: Hmmm - lower resistor values will raise the current and saturate the opamp more.The LM358 utilizes Class A/B output stages which are signal level dependable.With smaller signal levels Class A stage is used, but as the signal level increases the opampwill changeover to Class B - with a significant increase in crossover distortion as seen on the scope.Just my 2 cents/Peter

author: Insoft
author_rank: Newbie
timestamp: April 08, 2014, 03:11:06 pm
content: In the video you terminated the opamp you were using, first time I here'd of it so would be interested in seeing a video of why one should terminate a opamp and what happens if one dosn't.

author: Pilot3514
author_rank: Contributor
timestamp: April 08, 2014, 03:19:50 pm
content: Quote from: EEVblog on April 06, 2014, 12:20:51 pmIMHO, don't make it optional. Provide the torrent file on you website and not the video file. Those that want the video will use the torrent to get it.You will always want to seed it to make sure it is always available, but you can control the bandwidth.

author: David Hess
author_rank: Super Contributor
timestamp: April 08, 2014, 03:40:11 pm
content: Quote from: sportq on April 08, 2014, 08:11:21 amOperational amplifiers are often used as comparators because of their extra precision but an OP27 is one of the ones you have to be very careful about in this application because it has a very low differential input voltage range. The input stage has back to back input protection diodes across the inputs to protect it from excessive voltages beyond which the base-emitter junctions will break down damaging them via beta degradation. Your schematic does not show it but the input current is probably limited by resistance.Decompensated operational amplifiers like the OP37 fair a little better in comparator applications because they are faster.

author: Wim_L
author_rank: Regular Contributor
timestamp: April 08, 2014, 10:32:23 pm
content: If a specific opamp can be used as a comparator depends on the opamp. They're not optimal, but some will work. Some others will malfunction (sometimes in destructive ways). Even if an opamp can be used as a comparator in some circuit, performance may be bad. Some opamps perform poorly when recovering from being driven into saturation (and they likely will be, if you're using them as comparators). They'll be slower than comparators too. Still, sometimes it's a reasonable thing to use an opamp as a comparator, if you've considered all the issues and made sure they won't be causing problems for your circuit. Here's a good overview:http://www.analog.com/library/analogdialogue/archives/37-04/comparator.htmlLikewise, a comparator might look like it could be used as an opamp, but comparators lack internal compensation (that's what makes them able to switch quickly). Trying to use them with negative feedback is going to cause oscillations. So that really isn't a good idea.

author: David_AVD
author_rank: Super Contributor
timestamp: April 08, 2014, 11:52:45 pm
content: Finding comparators with push-pull outputs and more than 5.5V supply rating is surprisingly hard. There are a couple that go to 16V, but that's about it.

author: David Hess
author_rank: Super Contributor
timestamp: April 09, 2014, 12:04:43 am
content: Quote from: subolg123 on April 08, 2014, 11:26:05 pmPart of engineering is minimizing cost.If an spare operational amplifier can be used to replace a dedicated comparator saving a package, why not? I have also seen individual comparators like the LM339/LM393 externally compensated to perform the function of an operational amplifier. An LM324/LM358 is better being an operational amplifier and an LM339/LM393 is better being a comparator but the least expensive solution may involve using one in place of the other.One exception to the above that I have seen involves precision where a single slow but high precision operational amplifier replaces a comparator that would need a preamplifier anyway and speed is not an issue.

author: EEVblog
author_rank: Unknown
timestamp: April 09, 2014, 12:59:53 am
content: Quote from: Pilot3514 on April 08, 2014, 03:19:50 pmSo I should ignore several thousand people who want the RSS feed and force them to either go without or use torrent?I might as well stop the podcast version entirely and force people to download from youtube, that saves me a step and the hassle.

author: Pilot3514
author_rank: Contributor
timestamp: April 09, 2014, 03:31:18 pm
content: Quote from: EEVblog on April 09, 2014, 12:59:53 amI apologize. I did not know that people where getting the videos via the RSS feed. I watch them on YouTube from my mobile device. Also, while that look forward to every video, have yet to listen to an Amp Hour.

author: Unknown
author_rank: Unknown
timestamp: April 09, 2014, 05:15:22 pm
content: Superb!

author: Rigby
author_rank: Super Contributor
timestamp: April 09, 2014, 08:49:11 pm
content: Quote from: EEVblog on April 09, 2014, 12:59:53 amtorrent clients can automatically load .torrent files from RSS. It's a useful thing.

author: abdullahseba
author_rank: Frequent Contributor
timestamp: April 10, 2014, 08:47:35 am
content: will you do a video about electronics math

author: David Hess
author_rank: Super Contributor
timestamp: April 10, 2014, 11:19:18 am
content: On the subject of using operational amplifiers as comparators, I ran across a PMI (Precision Monolithics Incorporated) application note discussing this very thing. Most people will not remember PMI but they designed minor parts like the OP-07 series.Here is a link to PMI's Linear and Conversion Applications Handbook published in 1986 which discusses this on PDF page 119 which is PMI application note 25, Applying the OP-06 Op Amp as a High Precision Comparator.https://archive.org/details/PrecisionMonolithicsInc-PMI-LinearAndConversionApplicationsHandbook1986

author: EEVblog
author_rank: Unknown
timestamp: April 10, 2014, 11:45:00 am
content: Quote from: Pilot3514 on April 09, 2014, 03:31:18 pmand iTunes as well, which sucks the video form the RSS feed. Youtube hosting and torrent hosting don't work for this.

author: David Hess
author_rank: Super Contributor
timestamp: April 10, 2014, 12:43:40 pm
content: Quote from: EEVblog on April 10, 2014, 11:45:00 amWe discussed something like this over on the Yahoo Tektronix and other lists in connection with moving to a new host after the recent Yahoo fiasco and my conclusion was that the web and email accessible forum should work with a torrent tracker to index and provide updated torrent links to downloadable content which would be preferred simply to help manage bandwidth. Of course such a system is more complex but at least it should fail gracefully.The largest problem other than complexity is the one you identified; bittorrent is not the lowest common denominator and only a minority of users are setup to handle it.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: April 10, 2014, 04:30:58 pm
content: Crossover distortion was interesting for me, and I'd appreciate another video on ways that op-amps are non-ideal (aside from the bias current and offset voltage topics you've already covered.)

author: sergey
author_rank: Regular Contributor
timestamp: April 10, 2014, 07:39:09 pm
content: Yeah, crossover distortion was totally interesting. But i thought there'll be some feedback about summers here as well. Not as if i don't know how it works, but seeing more guys having an enlightenment on this is always really nice, hope you see what i meanOr maybe there're some folks who still scratches their heads and wants an urgent helpP.S. Application of the summer is also interesting to look into

author: David Hess
author_rank: Super Contributor
timestamp: April 10, 2014, 08:06:27 pm
content: My favorite example circuit for operational amplifiers is the differentiator because it teaches how to generate and use bode plots to establish stability.

author: sacherjj
author_rank: Frequent Contributor
timestamp: April 10, 2014, 08:13:54 pm
content: Quote from: Kirigozo on April 06, 2014, 05:25:12 amInstall many other browser plugins for video downloading and you can save the videos for watching off-line with no issues. You can also specify the video quality to trade off quality for size.

author: David Hess
author_rank: Super Contributor
timestamp: April 10, 2014, 10:22:34 pm
content: Quote from: sacherjj on April 10, 2014, 08:13:54 pmI do this with YouTube videos routinely with a Firefox plug-in although that limits the maximum resolution to 720p now.

author: sergey
author_rank: Regular Contributor
timestamp: April 14, 2014, 06:40:17 am
content: Just for the record for those who are not subscribed to w2aew's channel, he just uploaded opamp summing amplifier video. Really great video as well i'd say. Thanks man!

author: w2aew
author_rank: Super Contributor
timestamp: April 14, 2014, 12:56:58 pm
content: Quote from: sergey on April 14, 2014, 06:40:17 amThanks for the plug, Sergey!

author: Pilot3514
author_rank: Contributor
timestamp: April 14, 2014, 03:44:47 pm
content: Quote from: sergey on April 14, 2014, 06:40:17 amThat is a really good video, even better than Dave.

author: w2aew
author_rank: Super Contributor
timestamp: April 14, 2014, 04:02:52 pm
content: Quote from: Pilot3514 on April 14, 2014, 03:44:47 pmThanks, but I wouldn't go THAT far! Dave's videos are still among those that set the standard by which other are judged, IMHO.

author: sergey
author_rank: Regular Contributor
timestamp: April 14, 2014, 06:50:43 pm
content: Quote from: w2aew on April 14, 2014, 04:02:52 pmWell, it's a bit unfair to compare you guys in better/worse terms, it's just different styles! And this is really nice to have it different, really. So just keep doing awesome stuff in your own way

author: Rigby
author_rank: Super Contributor
timestamp: April 14, 2014, 07:57:07 pm
content: multiple styles are good. this is the thing about teaching and learning that many forget... no two people learn best in the same exact way. everyone has a history that contributes to the way they learn most effectively. There is no single learning or teaching type that works for everyone.The more videos on youtube about X from different authors, the better.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: April 16, 2014, 05:02:03 am
content: Every time I try to design any practical circuit for signal conditioning for photodiodes, piezoelectric pressure sensors or current sensor I always had to choose between different types of opamps like JFET input voltage-feedback amplifiers, or Current-feedback amplifiers (like AD8001 - how do I make it not to oscillate like crazy?), differential opamps, transimpedance opamps or instrumentation opamps and so on. Maybe it just me because I always measure things?I think there is definitely a lack of good introduction videos on practical applications of DIFFERENT TYPES of opamps. I would love to see second part of video that covers some of that.