Solving Op Amp circuits

[@saisivaram94]

In 10 minutes, you made me understand what I couldn't in 4 years of engineering! OpAmps no longer look like magic to me!! You are brilliant, Sir. I can never thank you enough.

[@DanBullard]

Thank you! I used to teach at a school where we analyzed circuits like that every day. The students got really good at op amps. Glad I could help.

[@anders5611]

That's concerning.

[@kirtandesai825]

My fours years at engineering school could not make me understand what you did. Thanks for this wonderfule content.

[@lor0the0fallen0angel]

Ok, this is PURE GOLD, to me at least. This is the simplest explanation ever I heard.

[@a.b.c.d.e...]

For some reason, this video I stumbled upon at 3am on (another) sleepless night has just hit the spot. You always just find these videos that either repeat things you already know, or are beyond comprehension complicated and you are lost in the first two minutes. There are always these thoughts where I think „yeah it probably works like that“ but I just never really believe it until someone says it out. This Video cleared a LOT of those up. Thank you so, so much.

[@christophermunozcortes2890]

This is priceless interview material. In several job interviews I've been asked to analyze the large-signal behavior of different opamps circuits with no equations and this technique has helped me A LOT! Thanks for posting Dan!

[@davefoord1259]

If you need something as basic as this on youtube to give you an advantage in a job interview then your training and experience is way below what you need to do that job. Youd be like the aeronautical engineer that thought its ok to cut heat traeted aliminium by laser cutting. Education these days is so poor if it results in qualified people that have that level of knowledge

[@gaynzz6841]

@@davefoord1259 based

[@DanBullard]

OK, OK! It was my first one! I will do some more and have already started a positive feedback version. Stay tuned!

[@ajeshpadmanabhan7948]

Thank you. Respect from india

[@ericmunene8521]

Thanks alot I really appreciate you from KENYA

[@seekinggod3174]

Very Good tutorial Dan, hope you can still share some more of your technical knowledge.

[@AlienRelics]

This is the best intuitive analysis of an Op Amp circuit I've seen. No complex math, just an understanding of a few simple concepts. The rules of an ideal Op Amp, Ohm's Law, and Kirchoff's voltage and current laws.

[@shobhrajsingh1177]

Sir, you helped me overcome 25 years of dread for op-amps... i can never thank you enough.

[@AutusDeletus98]

This is the first time I've fully understand how op amp works. Thanks a lot!

[@DansFlix]

You are very welcome!

[@spencerrenzbalinas7250]

Posted 8 years ago and it is more helpful than other sources i have been read and watched. Thank for this video I learned a lot about op amp

[@rhettscal]

Great tutorial! I went out and bought a HP6235 power supply just so I could recreate this lesson. It makes so much more sense now. Thanks Dan.

[@jeffanheier2775]

This guy helped me understand this in 4 minutes, vs my professor who teaches this in an hour and you are still confused afterward. Thank you sir, will be coming back to see more videos!

[@itzeltravels]

I usually never write comments on youtube videos but this was a great video. It made so much sense and it made something that looks complicated seem very simple. Thank you so much!!! I have gained back some confidence in my circuit solving skills. You should make more circuit solving videos, a video on how to design op amps according to a specification would be great.

[@qemmm11]

Ideal op virtual ground (v+=v-) Find the Circuit vo is not complexe and then v?v? .. ! Great explain Sir 😊

[@-_.---._.-_-.--._--]

Thank you very much! Up till now I just remembered the formulas for different types of basic opamp circuits, but now I actually understand where they came from and am able to tackle more complecated circuits.

[@GovernmentAcid]

WOW! Absolutely amazing tutorial. I'm currently back in school as a non-trad, and we're working with OpAmp circuits in my upcoming Electronics lab, and when I heard that that would be our second lab, I thought 'ACK! I don't know much about OpAmps, other than that they can be a big stumbling block', and having watched this, I feel much less intimidated. Thank you so much for posting this, this is absolutely amazing, and I'll probably be coming back to your channel as the semester goes on!

[@DanBullard]

Thank you!

[@ronaldlijs]

Hi Dan, Just to say that I'm 2 minutes into your video and I've paused it just to write this comment. EXCELLENT introduciton, to the point and the 3 rules here, more importantly the first one that I didn't really know about, are just great! I have seen dozens of Opamp videos, but no-one has put rule 1 into plain English: OBVSIOULY this is of GREAT help in understanding the OVERALL CONCEPT. EXCELLENT, I've learned something today, and I'm happy!!!! Keep it up!

[@douglasthomson1989]

Really great explanation of working through this op-amp circuit. Thank you very much for taking the time to do this. Cheers

[@rudyjudy7692]

Very logical step by step explanation. It has been a while since I worked with Op Amps and I am boning up for job related testing.

[@DanBullard]

Thanks! I wrote it to help a friend bone up for a test at GE She passed the test and got the job!

[@Joyrider58]

Superb explanation! This came at a good time for me, I just finished my Op-Amps class and I'm still wrestling with the circuit analysis. I've been falling back on the algebra formulas, but they don't provide real understanding. The steps 1, 2 and "3 with a twist" are great. Your approach, using the three op amp rules and Kirchoff's Law, provides clear and easy to visualize insight. I've looked at many op-amp tutorials, and this is my favorite, thanks for taking the time to share your knowledge.

[@DanBullard]

I've had several people challenging me to solve this circuit or that circuit. Let's not do that. Use the technique I show you here to solve the circuit you have in mind. Assume a voltage and see what happens. You can always start with the Vout at one of the rails and see where that leads you.

[@michaeldxyle]

Dan Bullard You assumed there is the same voltage on both inputs in each case (as per your rule 2) and then found a greater voltage on the output in each case? rendering your rule 2 redundant as you stated yourself? This makes no sense? how can you have no differential between inputs(considering firstly that this does NOT use negativr feedback) (ie. 2V on each input and then magically have 10V on the output? again reaching that conclusion by assuming one input is the same as the other "unless the output is greater" then finding that the output IS greater and still taking 10V as the legitimate answer??

[@andrewbradley1216]

I am wondering if by 'voltage supply' he means the plus/minus 10V attached to the op amp

[@DansFlix]

Yes, the power supply

[@relliart90]

Those people who dislike this...why? This explanation is so clear and superb!

[@andy-gee-2k]

you really know how to teach things. after all research, I think I really understand op amps now. thanks a lot

[@sam-pd6zi]

The way you did this numerical is fantastic and probably the best

[@memirandawong]

I wish you had more of these, but then again, this video was a quantum leap in my understanding of op amps

[@vladbio]

Simple, yet very helpfull tut. Thanks a lot. I loved that you mentioned that there is no current in the output too. It is very important sometimes for solving the circuit.

[@tboylu]

Sir this video you have been taken is just insanely good, is there any chance you could do RL, RC ,RLC and Op-Amp with RL, RC, RLC. I could not believe my eyes, how clear can someone teach something that shot time. Much love.

[@DanBullard]

Not likely, but I appreciate the comments. RL&C are just not that simple, although I did do a video on RC coupling.kzbin.info/www/bejne/fXikpWmEYrWtb9k

[@isabellet.3071]

Thank you very much! This has made Op Amps infinitely easier!

[@xxmountaindewxx7893]

Like an opamps open loop gain hehe

[@McGuire40695]

I really liked the video! I'm going to a 2-year tech school for electronics. I'm in my second semester of my first year. The way they do it here is split each semester into 3 5 week modules. This module (as well as the previous one) is all digital stuff, so I'm a bit rusty with calculating these circuits. Again, thanks for the video! It's a nice refresher!

[@michaelhawthorne8696]

One of the clearest explanations I have heard so far. Nice Vid Dan

[@ERJLifer]

+[Dan Bullard] , you sir were the first one to break it down easy enough for me to understand this, thank you very much

[@alogwe1]

Great video Dan! You are really good at teaching these concepts in a simple and elegant manner. Thank you for making this, please make more!

[@markhorton8578]

Brilliant, very clear, a good speed, a good amount of repetition/variance. Wish this was around when I was learning.

[@yimmygomez7173]

Holy shit! This explanation was the one I was waiting for! So easy to understand

[@emorag]

That was extremely clear and helpful. Thanks for posting this video.

[@almabrew8712]

You just save my ass for my tomorrow exam! Thanks

[@abouchraii3411]

Alma Brew i hope he save my ass too cuz i have an exam tomorrow xD

[@DanBullard]

a bouchra II Good luck!

[@ajays886]

This was the one of best video i found,thanks ❤

[@s11067528]

THANKYOU SO MUCH DAN...U SAVED MY LIFE...GOT MA FINALS 2MRW...ELCTRINCS...I DONT EVEN KNW THIS CONCEPT OF OP AMPS TILL NOW I HAD SOME LIGHT LOL...CHEERS MAN!! THANKYOU SO MUCH...U'R BEST!!

[@m34u2]

thank you. you are a life savior! I ' ve got an exam in two days and things begin to clear up. Can't wait for your next video :D Regards, Vlad

[@SravanParitala]

Dan! you saved a lot of time ... instead of reading and understanding, i simply understood everything... :D thanks a lot... Please upload more videos

[@sanjibbaral6951]

That was a great video. I immediately subscribed after watching this so that I do not miss your videos. That was just great.

[@canhnguyen7421]

Thank you for comming and sharing with me ! Thank one million !

[@miketo8]

You were showing the switch at 2v which corresponded to a Vout of 10v. You referenced back during this time to the initial switch position at 1v with a Vout of 5v.

[@Enigma758]

This is a great video and you have a talent for conveying challenging concepts. It would be wonderful if you created more videos like this about analog electronic circuit design!

[@DanBullard]

My newest -kzbin.info/www/bejne/i5zJg4ychM9mm5I

[@UnicornTactical]

thank you so much sir! clean and concise.

[@saab93secv]

Thanks! I love how clearly you explained the method (it's exactly what my prof seems incapable of doing)

[@nivekoblivion3784]

Dan, this video is so good. I have seen many online tutorials on op amps and this is by far the best. Why don't you upload more like this? You would become very popular very quickly. We need more lectures of this quality there are so few about.

[@mohammedabdulhakabdullaabd1121]

Very good explanation. Thank you.

[@sarahscott8307]

i never comment on youtube videos, but this was so helpful and articulately explained- THANK YOU!

[@gizzzmonic]

holly crap!! compair this to the video by the indian proffesor at MIT This is now too easy. Thank you sir

[@sudiptoborun]

Nice! What a nice way of explaining op-amps! Loved it.

[@guybar24]

Hi Dan , thanks for the video good job , can you please explain why do we need R4 and R5 ?

[@DanBullard]

We went from 5V out to 10V out. That's 5V. That change happened with a 1V change on the input hence the gain of 5.

[@christoffere425]

I don't get how you got the 2V and 1V at the beginning of the video 1:55 ? There is zero current, yes. But how did you find out that it only drops 1 volt over each resistor?

[@DansFlix]

The resistors on the left side form a voltage divider. 3 volts across 3K means 1mA is flowing, so each 1K resistor drops 1V,

[@christoffere425]

Thank you! Cold you also tell me why you removed the R5 resistor in the final step/task? (When we calculated the Req etc. )

[@DansFlix]

R5 came out while I was calcuating Requivalent because it will never have any current going in or out of it, so for the purpose of calculating Req it's best to just ignore it. We ignore the insulation on the wires because we know that no current flows through the insulators, so we don't need to concern ourselves with it.

[@DanBullard]

It's a classic voltage divider, 3V across a total of 3K resistance, 1mA flows, therefore each resistor drops one volt.

[@pnuema1.618]

Dan I am trying to learn electronics and I cant seem to get it. I think the problem lies in my approach or so to say my syllabus (which is me just randomly looking up things in no order in my quest) the question I have for you is.... where would you recommend I start?

[@Lexyvil]

Are the black arrows the same thing as ground? Thanks for the tutorial by the way.

[@Neverforget71324]

Think of it as the reference point (i.e. 0 Volts) for the voltages in the circuit. If you're using "ground" as "the reference point", then, yes. I've learned over the years to use "ground" carefully, because it has different meanings, depending on who you talk to (i.e. big difference if you're an electrician wiring up a house vs. an electronic tech fixing an amp).

[@Flintsmooth]

Good video. You could also mention that rule 2 applies only to closed circuits, where the output connects in some way with the - input, and the impedance therein does not prevent the max output voltage from being too low to match the input.

[@jimadams2473]

Dan, this is an excellent op amp tutorial. Love it. Thanks

[@tomfahey2823]

Excellent video - well paced, and very well explained.

[@zackcodi]

Awesome video sir how easily you solve the problems sir.Hats off to you sir.Thanks for uploading this video.Sir please upload some more numericals.

[@indiocolifa]

Awesome vid, clear concepts. Thank you very much. I' would love more circuit analysis videos!

[@irgski]

Thanks Dan for the very clear explanation. One suggestion would be to label the appropriate ref designators for the 3rd case equivalent circuit so the “student” can quickly identify which resistor is which.

[@kansasthunderman1]

I recall from a discussion with EE that when an op amp is used as a simple DC signal amplifier, the internal resistance of the input device itself (like a sensor coil) has to be included as part of total input resistance at the summing point. In that case the gain would actually be the feedback resistance / total input resistance.

[@DanBullard]

Yes, but sometimes it's hard to figure it out unless you do a static analysis like this.

[@CatsBirds2010]

Thanks for posting this problem.

[@imabeapirate]

question: Why have such a complicated feedback loop? What does it accomplish?

[@Roger49-x71]

Thanks, a very helpful video. But could someone explain the purpose of R4 & R5 or are they simply not needed if there's no current flowing through them and no voltage drop? Thanks in advance.

[@DanBullard]

R4 and R5 are just current limiting resistors in case something bad happens to the Op Amo.. That and in this case it allows me to make the point about Rule #1.

[@69lolwut69]

How do you get that 2V and 1V on the far left at the beginning of the video? Where is the math for that?

[@DanBullard]

faceinthegrass It's a voltage divider. 3/3 = 1. 1+1=2. That's the math.

[@Quinnosfavs]

Dan Bullard Put isn't the voltage divider rule R2/R1+R2 all multiplied by Vin to equal Vout. So from what ive learned in the past is that if both resistors are the same then the voltage will be halved? So 1.5V if you use the equation I use?

[@DanBullard]

Shane Quinn There are three resistors there, so 3V divided by three 1K resistors equals 1mA through each one. One milliamp times 1K = 1V, so each resistor has 1V across it. zero plus one is one, so the voltage at the top of R3 is 1V. One plus one is two, so the top of R2 is 2V. And 2 plus one is three, so the top of R1 is 3V, which all works.

[@fog1257]

Unbelievable how easy you make it seems with this short video. Thank you! I have one question, what is the purpose of R4 and R5 in this case when there isn't any current flowing there?

[@DanBullard]

This circuit is used to test an interviewee's knowledge, so the purpose of R4 and R5 is to see if the interviewee knows that no current ever flow into or out or the inputs.

[@fog1257]

@@DanBullard Aha! Thanks for the response. I hope you will keep doing these videos, good teachers with good knowledge are rare.

[@relaxationTherapy001]

superb !! I've never got this much clear explanation even in my university classes..

[@nevis2769]

Why is there no voltage drop across R5? 2:30

[@welltekdiagnostics6835]

Very Good Circuit Analysis ,The Way you say it ,it shows you are a teacher ,,I disagree with some of it ,but bottom line VERY Good Troubleshooting . and thats how we learn from each other .

[@maasteeve]

Verry clear and helpfull video, I have an exam tommorow and some of these rules could be of use thank you

[@michaelbaucum6787]

Hi, I have a question. If there's no current flowing through R4 and thus no voltage drop across it, then what's the purpose of R4 in the first place? Thanks in advance.

[@DanBullard]

I get asked this all the time, I should have addressed it in the video. Most often it's not a good idea to hardwire a power supply into an input, digital or analog. If the pin shorts out internally, something bad could happen. Better to limit the current than letting one faulty transistor set the chip and hence the device on fire!

[@michaelbaucum6787]

Thanks for your quick response!!

[@jimmysyar889]

I was looking for this comment ! 👌🏻

[@waleedabouelwafa262]

a very helpful example,,,thank you for releasing this video,,, but how did you figure the gain in the second step 5V/1V?? ,,, while the Vout =10 and the Vin=2 ,,, is the gain supposed to be 10V/2V?? thanks again.

[@DanBullard]

Exactly. Lots of profs teach some mathematical solution to gain, but the best way that I have found is just to do analyze the circuit with a couple of values to see what the DC gain is. No capacitors or inductors, no worries about AC gain, it's the same as DC gain (pretty much). I once got through an interview at Tektronix with this strategy and got the job.

[@waleedabouelwafa262]

Dan Bullard yes indeed ,,, its a very good strategy. thank you.

[@levialmuina]

I need some clarification on that. Did you open the capacitors and short the inductors ans analyze as DC?

[@alphonsesynrem28]

My my it's really a good insight to use opamps for many different things. Thank you.

[@psmdhaneef]

Thanks for the help. I hope the rules you said has got no error in it.

[@bitsurfer0101]

This is definitely a simplified look at Op Amps. Would you be able to create a tutorial on bjt transistor biasing?

[@berkaykaya3054]

perfect narration.

[@malwaysfine]

Hi Dan, I am delighted with this logic. I don't understand why degrees don't teach this way?! Thank you. I haven't checked the other videos but are there different config which uses L and C?

[@DanBullard]

Thanks, I haven't done anything with L and C. I worked on RADAR and radio, so I do know a fair bit about it, but I'm working on Harmonic Distortion mostly right now.

[@malwaysfine]

@@DanBullard Thank you again. I have always been fascinated by OPAMPs, quite a powerful component.

[@WisdomVendor1]

Just an adjustment to your rules. If there is output feedback to the inverting ( - ) input, rule 2 applies unless V(out) is beyond the range of the rails or source.

[@DanBullard]

Yeah, but... It's easier to just let someone do the analysis ignoring what might be feeding back to what. What happens when you have both negative and positive feedback? Who knows, until you analyze it.

[@jamesladd471]

Terrific, but what is the point in recalculating the voltage at the negative input terminal ? Jim

[@DanBullard]

Because I have to prove Rule 3.

[@user-fj5yt1ls1o]

amazing explanation! Is there any video in ur channel? Cuz i couldn't find any other lesson except this.

[@DanBullard]

I'm back to working on videos every day, so stay tuned. Try my Harmonics playlist here: kzbin.info/aero/PLUJ3dFf_Ca8RAISZMJb50Eof_UZExQy6T

[@sibilakshman9575]

Great video , I have a doubt if the potential at the terminals turn out to be different would that not make the op amp non ideal ?

[@DanBullard]

This is not about "idea" op amps, that is what happens in real life. There are plenty of videos about fantasy devices, just watch almost anyone else's video on Harmonics, all of that is fantasy.

[@Sneee3]

Thank you so much for this video. Keep up the great work, it's super appreciated! Greetings from Sweden.

[@Rovershastalamuerte]

thank you for doing this video. Really helped me to understand a circuit i am making with the lm324.

[@franklinelel]

Thank you for the great explanation. What are the rules for non ideal Op-amp?

[@DanBullard]

The Op Amp datasheet is the best place to look for that. Input bias current is spec'ed as well as input offset voltage. Some Op Amps have such high input impedance that Rule 1 is true no mater what. The point is, your first attempt at solving any circuit would be to assume that my rules cover all cases. If you see a 20MOhm input resistor then you should understand that that large an input resistor MAY have some impact on the input voltage, but it is by no means guaranteed.

[@simonyoungglostog]

Excellent. We need simple numbers when first learning about this.

[@DanBullard]

This video got my friend Martha a job at GE. Glad I could help you.

[@simonyoungglostog]

@@DanBullard I recently suffered some minor brain damage and lost a lot of my maths abilities. I'm slowly relearning them, so I find electronics calculations really useful. Thanks again.

[@r0n_aw]

How di you calculate the equivalent resistance of 1.666k and could you explain the 6mA running through R9 please? (around 8:00)

[@DanBullard]

Starting from the output of the op amp, everything is in series with R9. Then, R8 goes straight to ground while R6 and R7 are in series with each other but, as a pair are in parallel with R8, as shown in the equivalent circuit on the far right. Now. R6 and R7 add up to 2K, and 2K in parallel with R8 (1K) is (2K*1K)/(2K+1K) = 0.6666K. And since that is in series with R9, 1K in series with 0.66666K is 1.66666K. Remember that we have to forget about R5, since no current is going to flow into R5. It's like a resistor floating in the air as far as we are concerned. Now, truth be told, you might get a nanoamp flowing into our out of the op amp (or less!) but what difference will a nanoamp make to your calculations? Far less than the tolerances of the REAL resistors.

[@Raxarax]

Are you serious? This is one of the best vids I've seen on op-amps... So I go to your videos to watch more! Vids on diodes and BJT's and all the other stuff I need to learn and there's nothing...

[@chemieprof]

Thank you for posting this video! What is R4 supposed to do?

[@DanBullard]

Good question! R4 is supposed to a) Limit current in case of a short circuit failure so the chip doesn't burn up and start a fire, and b) create a voltage drop on the Plus side equal to the Minus side if any current does flow into the inputs. Rule #1 is always true, no current flows into the inputs. But a very tiny bit may flow, not enough to worry about when you are trying to figure out the circuit, but perhaps a little tiny current might flow. If it does, the other input will probably draw about the same amount of current, and so the two input resistors will create an equal voltage drop preventing an offset voltage from changing the output. For the most part, it is best to just assume that no current will flow into the inputs.

[@chemieprof]

Ohh, okay! Thank you!

[@belleluze]

if no current goes in the inputs then what's with the 1k/R4? thanks

[@DanBullard]

To make the point, there is no current flowing. Can't prove it without a resistor. Watch my most recent op-amp video kzbin.info/www/bejne/i5zJg4ychM9mm5I

[@belleluze]

@@DanBullard I see thanks Mr Bullard!

[@Lexyvil]

Can anyone tell me how he got 2V between R1 and R2 at 1:58? I'm guessing he's using voltage divider, which I did the same but only obtained 1.5V, using 3*( 1k / 1k+1k )

[@DanBullard]

You have 3K Ohms spread between 3 volts. There is no other current path through, or around R1, R2 and R3, because, as I state very clearly there will be no current flowing into the op amp, so R4 is a trillion ohm resistor as far as we are concerned. 3V/3K = 1mA, 1 volt will be dropped across each resistor, R1, R2 and R3. There is no 1.5V anywhere, unless you somehow got current to flow into the op amp, which is an absolute impossibility.

[@Melloyallo3434]

I'm sure you 'd get a lot of responses for videos on Diodes and BJT's and other stuff. This video was awesome !

[@ifthekharahammad5909]

I might be a little bit too late to join the party 😄 I appreciate the clear explanation and detailed solution you provided. Sometimes we all forget that electronics is not that complicated and that all circuits can be handled by simply adhering to a few basic laws. I have a question, and I would greatly appreciate it if you could help me understand the design decision: what is the purpose of R4 and R5 in this circuit?

[@DanBullard]

R4 and R5 are typically placed there to keep the current down to a minimum if the Op Amp fails, but in this case they are used to trick the observer, to see if they understand that an Op Amp consumes no current on the inputs. It's a standard ploy imposed on Employee Applicants.

[@ifthekharahammad5909]

@@DanBullard I appreciate your response. They were current-limiting resistors in my mind. Although it's a wonderful concept, I've never utilised them in any designs. In my subsequent design, I'll give it a shot.

[@TechTins_Projects]

This is so elegant. Many thanks for this. Where can I find details on the Jim Harris method? I can't find any references to Jim Harris anywhere? Did he write a text book?

[@DanBullard]

He was an obscure man who built a small school in Silicon Valley called Technical Training Center. He was a genius at simplifying difficult concepts. He's gone now but many engineers and technicians learned everything from Op Amps to uPs just this way.

[@BitBerlin]

Dan Bullard So, who will train the young Padawans in the secrets of the Force so they become Jedi Knights just like you, Oh-venerable Grand Master?

[@hils5183]

Hi Dan, Do you know how synchro- servo systems work? I really like your videos they've helped me a lot. Do you think you can do a video on sychro servo systems? I have not seen any videos anywhere.

[@savageworf]

Hi Dan, The gain is also defined as Vout/Vin. Won't that work as well for this problem? You then won't have to find a change in the output for a change in the input.

[@valko007]

Dan you made electronics loom very easy , i applaud you sir,

[@luise.batres6436]

Excellent tutorial. Something that confused me was R4. I did the calculation with a Voltage divider with a Load (R4) and I got a different Volatge for the +Input. therefore if I analyze your schematic, Omitting R4 (because there is no Curent flowing through it,) will I get the same result? And if so, why is it necessary to include it in your example? Is R4 a mock component?

[@DanBullard]

+Luis E. Batres Generally, on sensitive input pins we like to protect them from too much current in case the pin shorts internally. The circuit will fail if that happens, but without a resistor, the whole box might catch fire. This is especially true on MOSFET circuits, because the gate is just a capacitor with a very thin insulator to keep the thing from blowing sky high.

[@luise.batres6436]

+Dan Bullard Thank You for your response. I am still conflicted though; because if as Rule 1 states: there is no Current going into the Inputs of a Op-Amp (for an Ideal Op-Amp that is, because of the High input Z of about 1M ohm for a Real Op Amp.) is your Low Resistance (in R4: 1k) helping in any way to prevent Damage or Over Heating?

[@DanBullard]

+Luis E. Batres Because if the input shorts, the max current will be only in the milliamps. Some engineers bias op amps right from a power supply line capable of 10s of amps. What if the op amp fails and you have no resistor on that line? Even if in normal conditions the input Z is a megohm, if it shorts, (either internally or externally) you'll have grounded a 100W power supply which will probably burn up the runs on the board or start a fire in the component or elsewhere in the circuit. It's easy to use a power supply line to provide a static "1" or "0" to a digital circuit IC for example, but if the device shorts out internally, your power supply can now dump 10s of amps into the chip causing a real safety issue. A nominal resistor, say 1K, will not reduce the voltage much on a high impedance pin, but may prevent a fire, and that alone is a good reason to have a resistor on those pins.

[@luise.batres6436]

+Dan Bullard Ok. Now I get it. So R4 is not cecessary in this "simple" circuit, but it is of Utmost Importance for the protection of other Circuits in ase this one fails. Thank You for the clarification and your excellent Analysis of an op-amp.

[@ShannonNewbold]

+Dan Bullard I had the same question too. I am assuming the same explanation holds for R5.

[@squaresolid444]

Very nice tutorial, Dan! thank you! I hope you have more tutorials on Op-Amp application, you did really good job in explaining!

[@sam-pd6zi]

Can u make videos on solving cmos/pmos configurations