Op Amps: Single Supply Biasing

[@Manticore1960]

The most straightforward & understandable explanation I've seen on KZbin. 👍

[@lezrekmohamed]

Thanks for the educational video. I have made a 3005 lead 12 Marshall preamp. It works well with +17/-17 volts. I tried to make it work with a single power supply using biasing like you showed. It worked with Tl072 but heavily distorted. But didn't work with the original 1458 and JRC4558. What changes should I do to make it work.

[@ElectronicswithProfessorFiore]

To be honest, I probably wouldn't bother with the 1458/4558 as they are not the best quality compared to what's available now. +/-17 VDC on a TL072 is really pushing the envelope. A single +30-ish supply should not distort any more than the split supply. If it does, something is up. I suggest checking the inputs and outputs to see if they are, in fact, biased at half of the supply rail. All it takes is one coupling cap to be disconnected and everything goes out the window.

[@bradeureruwoan8288]

that's what i want for portable Lithium 18650 battery supply op amp project,there is low DC supply op amp in LMV version 😊

[@dnkreative]

Great example. How to compute a value of Cby? What it depends of?

[@ElectronicswithProfessorFiore]

Determine your lower frequency limit and then use the standard fc=1/(2piRC) formula. R is the Thevenized resistance around Cby (R1//R2//R3 to a first approximation).

[@mortenlund1418]

Thanks for sharing. Great video.

[@urlkrueger]

I am wondering with the last circuit if 120Hz in the input signal would be attenuated.

[@ElectronicswithProfessorFiore]

Generally speaking, no, at least not by the power supply bypass network. The lower frequency limit of the circuit is a function of the input and output coupling caps and associated resistances, plus the feedback cap and Ri. That's about 3 Hz for the feedback, 1.6 Hz for the input and output coupling networks. Obviously, you could change the values to attenuate 120 Hz on the input signal but that's not the goal of this circuit.

[@simonyoungglostog]

Excellent, as usual.

[@greggchapman2677]

By the way, these are EXCELLENT videos

[@monterok006]

4:37, what? C in is going to react with r1 and r2 unless we have a "high source impedance"? I'm so confused, i thought the signal would not influenced more if source have very low output impedance..

[@monterok006]

I think it's the input impedance, not source impedance?

[@ElectronicswithProfessorFiore]

@@monterok006 You have to Thevenize around the cap. Looking to the right you see R1//R2//Zin of the op amp. To the left you see the internal impedance of the source. Add these two parts. That's the effective R.

[@frgeret4970]

can I connect positive voltage to the negative supply input so that the supposedly inverted input would get inverted again?

[@ElectronicswithProfessorFiore]

Only if you also want to blow up the op amp ;-) Most op amps will die a quick death if you swap the power supply leads.

[@Hellcommander245]

Is there any reason we can't just create a split supply using a voltage divider (calling 1/2 Vcc ground)?

[@ElectronicswithProfessorFiore]

Essentially, that's what we're doing here. It's just that "ground" is properly understood as being the reference rather than true ground. Just remember that your "1/2 Vcc ground" isn't the same "ground" as used by the source (and mostly likely, the load), hence the need for coupling caps. Sometimes we need to be careful about our terminology. I will add, though, that in a multi-op amp circuit, you could set up a "master voltage divider" and connect the op amps to the appropriate rails rather then set up dividers at each op amp. This requires a little forethought regarding keeping the DC gains of each stage at unity.

[@JohnJohnson-ml2ll]

Great video! I’m actually reading your textbook right now for my IC class. Quick question: why do Ri and Cf create a lead network and not a lag network? The resistor is placed before the cap making it a lag network, no?

[@ElectronicswithProfessorFiore]

The order of Ri and Cf makes no difference here. It's not a true lead network but it behaves like one. Gain is Rf/Ri + 1. But as f decreases, you can no longer ignore Xcf. That is in series with Ri and the resulting complex impedance magnitude increases as f decreases. That means the gain decreases as f decreases, just like a lead network. The gain does not "roll off forever", though. At some point that impedance >> Rf and the gain falls to one (i.e., the DC gain is unity). Quick question for you: Are you using my text as a supplement or is it the assigned text for the course?

[@JohnJohnson-ml2ll]

@@ElectronicswithProfessorFiore Ah! I see, that makes sense. Thank you so much for your reply Professor. To answer your question: Your textbook is the assigned text for my course. I attend Thomas Edison State University Online.

[@ElectronicswithProfessorFiore]

@@JohnJohnson-ml2ll Cool. Do you like the school and the courses? Seeing that it's online, how do they have you do labs? Is it via simulation, do they give you parts kits, or...?

[@JohnJohnson-ml2ll]

@@ElectronicswithProfessorFiore For the most part, yes! It’s a decent institution and the bachelors I’m going for is ABET accredited. Essentially, half the labs are through the Multism simulation software and the other half are physical. The syllabus gives you a list of required material and components to order online, from a website of your choice. Amazon is usually the best bet. Biggest gripe: online institutions are typically quite liberal about giving credit for classes they think you’re already proficient in, especially if you have technical training from the military (my situation). Thus, I was advised to skip over solid state electronics and jump right into OpAmps/ICs when in reality I only have a VERY basic understanding of transistors and stuff like that. However, I’ve been going through your videos to fill that knowledge gap. So thanks! :)

[@ElectronicswithProfessorFiore]

@@JohnJohnson-ml2ll In that case, DEFINITELY grab my Semiconductor Devices text, if you haven't already done so.

[@talatyavuz7000]

Is R3 a must to deal with supply noise? I could not understand its function.

[@ElectronicswithProfessorFiore]

When you add the bypass cap on the divider, without R3 the Zin would be zero. Ideally, the junction of R1, R2 and the bypass cap would be at ground. Adding R3 prevents that from being the case for the input signal. R3 winds up setting Zin.

[@talatyavuz7000]

Oh I see, Thanks a lot.

[@stephant913]

Please tell what is the SW you are using.

[@ElectronicswithProfessorFiore]

TINA-TI, available from ti.com

[@engineeringjoe]

What software do you use for simulation?

[@ElectronicswithProfessorFiore]

TINA-TI. It's the free version of the TINA simulator, available from Texas Instruments (ti.com). Check out the Simulators playlist for details.

[@horacepoon7044]

Great! Thanks.

[@asam982]

Good job ❤️

[@greggchapman2677]

Why don't Electrical Engineering instructors in academia teach students to DECOUPLE the power supplies on an op-amp with one or more capacitors. This is an expectation in the electronics industry. I don't think that it is wise to introduce a zero by adding a capacitor in your signal path in order to reject supply noise. If you decouple the power supplies directly, it does not effect your bandwidth. - Dr. Gregg Chapman, OSU

[@ElectronicswithProfessorFiore]

Well, I can't speak for other instructors, but that is something that is stressed in my op amp text and lab manual. And certainly, I have seen it in other texts. As far as this video is concerned, ultimately, the point of Cby in the latter part is to bypass the supply, and it may be more efficient there than placing the cap directly across the supply (as is typical), where you're dealing with a much lower source impedance. I probably should have been more specific about that. Anyway, as they say, there's more than one way to extricate the epidermis from a feline.

[@greggchapman2677]

@@ElectronicswithProfessorFiore I have never seen these solutions with an AC path to ground. This is really great stuff. Your discussion of introducing zeros in the single supply solution is excellent. Can you give me a link or reference to your text and lab manual. I would like to review it for potential use here at OSU. Best Regards - Gregg Chapman

[@ElectronicswithProfessorFiore]

@@greggchapman2677 The links are in the description of this video. All of my texts (5) and lab manuals (7) are free Open Educational Resources using a Creative Commons license. They are available in PDF and ODT formats (thus, you are free to modify them as needed for your coursework). Very inexpensive print copies are available from Amazon along with Kindle versions. I'm sure your students will like them. You might want to check out the faculty reviews at U of Minnesota OER portal open.umn.edu/opentextbooks/textbooks?term=fiore If need be, you can contact me directly at the email address found in the front matter of the text.

[@ElectronicswithProfessorFiore]

@@greggchapman2677 I forgot to add: if you do a 'net search on the title of my op amps text (Operational Amplifiers & Linear Integrated Circuits: Theory and Application", you might get hits from older editions. The first edition came out in the early 90s and was published by West. The rights were sold to Thomson/Cengage and a second edition was published in the early 2000s. I was able to get the rights back and released the 3rd edition as a free OER a few years ago. You do not want the older editions as they contain now obsolete parts and do not have the newer ICs found in the 3rd edition.