stabilizing opamps - Page 1
Forum section: electronics / beginners

author: Kirigozo
author_rank: Contributor
timestamp: November 10, 2013, 12:06:44 pm
content: Hi folks,I'm looking for documentation describing the principals and procedures for stabilizing op-amps in circuits similar to linear voltage regulators. All I've been able to find talks about audio circuits.Any relevant resources will be appreciated.TIA

author: Kremmen
author_rank: Super Contributor
timestamp: November 10, 2013, 03:10:47 pm
content: The principles are those of general control theory. It is a large subject not digested in an afternoon, but you do have to start somewhere.My suggstion - start here:http://www.ti.com/lit/an/slod006b/slod006b.pdf. Chapter 5 discusses feedback and stability but be aware that you need to be comfortable with all the preceding material before ch 5 really opens.After that there is no end of additional material delving deeper into the subject.

author: Kirigozo
author_rank: Contributor
timestamp: November 10, 2013, 04:58:08 pm
content: Thanks but I'm looking for something that bridges the gap between the theoretical and the practical.

author: Rory
author_rank: Frequent Contributor
timestamp: November 10, 2013, 05:39:44 pm
content: Quote from: Kremmen on November 10, 2013, 03:10:47 pmThanks Kremmen, This is a great resource! Not sure if Kirigozo realizes what you just handed him...Kirigozo - when it comes to opamps, there isn't that much of a gap between theory and practice... apply the formulas, check the results and tweak if necessary. About the only things you need to be concerned with in practice that aren't purely theoretical are component tolerances, temperature coefficients and parasitics.

author: Kremmen
author_rank: Super Contributor
timestamp: November 10, 2013, 06:05:22 pm
content: Quote from: Kirigozo on November 10, 2013, 04:58:08 pmSo you just want the answers but don't want to sweat for them? Sorry no dice - it doesn't work that way. You used the word principle yourself. The principles are outlined in the paper i linked. Master them or stay out in the cold.

author: Kirigozo
author_rank: Contributor
timestamp: November 11, 2013, 03:55:07 am
content: Quote from: Kremmen on November 10, 2013, 06:05:22 pm

author: tsmith35
author_rank: Frequent Contributor
timestamp: November 11, 2013, 04:11:26 am
content: Quote from: Kremmen on November 10, 2013, 06:05:22 pmI think the bridge between theory and practice is ... experience. Read the information, then try it out in the real world. There are many, many books available to help you:http://www.amazon.com/s/?field-keywords=practical+op+amp(190 results)This reminds me of a discussion in a model rocketry forum where they were discussing formulas for rocket stability. One guy posted a long, detailed series of formulas and theory, then made a comment along the lines of, "I tried to simplify this as much as possible, but I guess it really is rocket science"

author: Kremmen
author_rank: Super Contributor
timestamp: November 11, 2013, 06:28:52 am
content: Quote from: Kirigozo on November 11, 2013, 03:55:07 amAhh - attitude. The TV sitcom replacement for competence. OK, if you think that will work then good luck to you. Let us know when that helped you solve the first nontrivial case.

author: tsmith35
author_rank: Frequent Contributor
timestamp: November 11, 2013, 07:40:36 am
content: Quote from: Kremmen on November 11, 2013, 06:28:52 amI find it humorous that Kirigozo first says,Quote from: Kirigozo on November 10, 2013, 12:06:44 pmThen he says,Quote from: Kirigozo on November 10, 2013, 04:58:08 pmThen his final response is,Quote from: Kirigozo on November 11, 2013, 03:55:07 amPerhaps it would have been easier if he had simply asked someone to provide him with an amazing resource (other than an excellent TI book that is widely recommended for learning about op amps) that would teach him everything he needs to know about op amps without actually having to study anything. Kind of like in The Matrix... "Tank, I need a pilot program for a B-212 helicopter ... Hurry ... Let's go."If only learning about modern technology was so simple...

author: Sigmoid
author_rank: Frequent Contributor
timestamp: December 11, 2013, 04:59:19 pm
content: Ah yes general control theory...My love and passion from my university years... not. XDAnyway, as painful as it is, I guess it can be really useful. (Ie. you can't really do anything serious without it.)Also, I find Laplace transforms somewhat Lovecraftian, so it's kind of cool.Oh and Op Amps for Everyone is really cool.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 12, 2013, 06:54:33 pm
content: nyquist and bode plot. thats the bridge! the other bridge is, like someone said "alot of sweat". there is another bridge "stay in the cold" type, buy one ready made.

author: Kirigozo
author_rank: Contributor
timestamp: December 13, 2013, 01:06:25 pm
content: I'd like to thank you guys for reminding me how good I am at doing research. I don't need the help of the over qualified who can do no more than repeat phrases they highlighted in text books. You see, I found exactly what I was looking for in places you wouldn't think of looking.BTW Smithy, modern technology is simple; if you haven't discovered that yet, you are in deep do-do.What more can I say but

author: c4757p
author_rank: Super Contributor
timestamp: December 13, 2013, 01:09:33 pm
content: Dude. Stabilizing circuits ishard. Nobody can tell you how on a forum. You really need to go research control theory a bit. This is one of the places in engineering where we have yet to find a way to chase out the mathematics. You need to cozy up with equations a bit (some of them complex - pun intended).Start with Bode plots.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 13, 2013, 01:46:50 pm
content: Hi,To the original poster.In this thread I show how to measure the bode plot of an op-amp circuit, using LTspice.In this thread I measured the control loop using hardware.https://www.eevblog.com/forum/projects/dynamic-load-bode-plot-using-hp-35665a-dsa/msg310991/#msg310991Regards,Jay_Diddy_B

author: prenato
author_rank: Regular Contributor
timestamp: December 13, 2013, 01:56:51 pm
content: I second the recommendation for Ron Mancini's apnotes. This other one from him on stability is very good too:http://www.ti.com/lit/an/slyt087/slyt087.pdfI ran into opamp stability issues when implementing the constant current load and this was a life saver.A good book with practical considerations (and just the right amount of theory/math; it's really needed here) is "Design with Operational Amplifiers and Analog Integrated Circuits" by Sergio Franco

author: Kirigozo
author_rank: Contributor
timestamp: December 13, 2013, 02:14:54 pm
content: Quote from: Jay_Diddy_B on December 13, 2013, 01:46:50 pmJay,I think I am going to enjoy consuming your threads. I think it is going to be very useful.Thank you very much, it really is appreciated.

author: SeanB
author_rank: Super Contributor
timestamp: December 13, 2013, 06:48:24 pm
content: Stability, or why is my amplifier an oscillator, and why does my oscillator not.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: December 19, 2013, 04:16:06 pm
content: Speaking of control theory, it's been a while since university, and we mostly concentrated on abstract systems...So I'm wondering if anyone could suggest me a good exercise book to get going with the practical task of taking a semi-simple circuit with discrete active and passive components, and getting to its complex freq domain transfer function...(Yea I'm feeling masochistic.)