hybridfree/eevblog-posts huggingface dataset:
Op Amp (LMV321) Operating Near Rail Voltage - not working - Page 1
Forum section: electronics / projects

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: November 03, 2019, 02:13:05 pm
content: See the circuit in the picture...The main GPS module (top right) sends 3.3V (3.287V measured) out of VccRF and that is fed back into V_Ant via a 10resistor (R2). The 3.3V from VccRF also goes across a potential divider (R9+R10) which feeds a voltage of approx 3.1 V to the + input of U1.1, the LMV321 Op Amp.If the antenna is connected it pulls approx 25 mA and there's a voltage drop across R2 and I measure 3.057 V on the - input of U1.1. If the antenna is disconnected, there's no voltage drop across R2 and I measure 3.287 V on the - input of U1.1.Here's the problem; the output of U1.1 (pin 4) stays at 60 mV all the time (it does so on 2 PCBs I have made and tested) but my logic says that, because the - input of the Op Amp changes from above to below the voltage on the + input, I should see the output swing from rail to rail.Is there something wrong with my understanding on how this should work? I adapted the circuit from fig 14 of the Ublox MAX-8/MAX-M8 Hardware Integration Manual where they use a LT6000 Op Amp and R2 is 560. I have tried a 560resistor but it doesn't change the behavior. Is the LT6000 a way better Op Amp or can you guys suggest an alternative if the issue is my cheap Op Amp selection?Thanks in advance. I think it's because the LMV321 only works for input voltages up to Vcc - 1V while the LT6000 allows inputs all the way up to Vcc, if there's alternatives, I need a device in the SC-70-5 package.

author: China NewBoy
author_rank: Regular Contributor
timestamp: November 03, 2019, 02:43:56 pm
content: did you measured the opA's Vcc?

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: November 03, 2019, 03:00:53 pm
content: Quote from: China NewBoy on November 03, 2019, 02:43:56 pmYes, it was 3.287 Volts.I think I've found a replacement, Texas Instrument's TLV313-Q1 which features RRIO (rail to rail input output)

author: Zero999
author_rank: Super Contributor
timestamp: November 03, 2019, 07:30:26 pm
content: Yes, I think you're right: The LMV321's input common mode range only extends to 1V less than the positive supply.There are plenty of op-amps with rail-to-rail inputs. The TLV313 is a sensible choice. Also try the MCP6021.http://ww1.microchip.com/downloads/en/devicedoc/20001685e.pdf

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: November 03, 2019, 09:42:29 pm
content: It seems that the MCP6021 doesn't have the same pinout as the LMV321 but the TLV313-Q1 does. I have 75 PCBs made.

author: Gandalf_Sr
author_rank: Super Contributor
timestamp: November 09, 2019, 02:13:40 pm
content: So I dropped in the TLV313-Q1 to replace the LMV321 (same footprint and pinout) and all works as expected now
Op amp -10 dB/dec gain roll off for capacitive load compensation - Page 1
Forum section: electronics / projects

author: axitece
author_rank: Contributor
timestamp: December 28, 2017, 03:01:04 pm
content: Hello everyone,I've been reading a chapter titled "My Approach to Feedback Loop Design" in aJim Williams bookthat goes into detail on how to design feedback loop that is stable for a large range of capacitive load values. It has been very helpful in understanding different approaches, however, at the end of the chapter the author uses a technique that I haven't heard of before.A brief summary of it is that we get instability due to the addition of 90 degree phase shift from capacitor in addition to the 90 degree shift from the op amp. If we could limit the op amp's total phase shift to 45 degrees, then the 90 degree phase shift (at whatever frequency) would still leave us with phase margin of 45 degrees. In order to achieve this, the author creates a circuit similar to what's shown in the figure below which approximates -10 db/dec roll off near the UGF.I'm interested in hearing others' opinion on this approach to compensation as well as any other techniques that might be out in the wild that might be worth sharing. Thanks!

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2017, 11:27:45 pm
content: The schematic looks odd. I don't think I've seen a configuration like that before.It doesn't look right. There's no DC negative feedback path, so it won't work.

author: Wimberleytech
author_rank: Super Contributor
timestamp: December 30, 2017, 02:35:33 am
content: Missing pieces for sure

author: axitece
author_rank: Contributor
timestamp: December 30, 2017, 02:38:35 pm
content: Quote from: Hero999 on December 29, 2017, 11:27:45 pmSadly this is all that is shown in the book :/This is only book/technical literature that I've come across that addresses stability for any capacitive load. Does anyone on the forum know of any other approaches? Thanks!

author: rstofer
author_rank: Super Contributor
timestamp: December 30, 2017, 03:42:00 pm
content: What does LTspice say?Op amp integrators don't have a DC path (in the sense of a resistor) for feedback either. Of course they don't tend to drive highly capacitive loads.http://www.electronics-tutorials.ws/opamp/opamp_6.html

author: Zero999
author_rank: Super Contributor
timestamp: December 30, 2017, 07:56:48 pm
content: Quote from: rstofer on December 30, 2017, 03:42:00 pmIt's not good design practice though. The DC gain should be limited to a known value, otherwise it will amplify the offset, causing the output to saturate.
op amp  AGC  - Page 1
Forum section: electronics / projects

author: salviador
author_rank: Regular Contributor
timestamp: May 22, 2020, 12:13:11 pm
content: Hi,I want to create an AGC with op-amp and an input dynamic that varies from min 40mVpp to max 700mVpp with a constant voltage output.This circuit work with MC33078Pthe problem arises when I replace op amp with another type lm358, why ??

author: David Hess
author_rank: Super Contributor
timestamp: May 22, 2020, 07:53:12 pm
content: The difference in input bias current may be preventing the logarithmic stage from working properly. It needs a better way to handle positive inputs.

author: Zero999
author_rank: Super Contributor
timestamp: May 22, 2020, 08:33:15 pm
content: What do you mean by not working?The LM358 has lots of crossover distortion, so if the output looks bad, that would explain it.

author: David Hess
author_rank: Super Contributor
timestamp: May 22, 2020, 08:45:52 pm
content: Quote from: Zero999 on May 22, 2020, 08:33:15 pmI mean the logarithmic amplifier behaves poorly when the AC input goes positive; it has no way to sink a positive input.QuoteYou could force the LM358 into class-a mode by loading the outputs to either supply rail with load resistors.

author: salviador
author_rank: Regular Contributor
timestamp: May 23, 2020, 10:07:06 am
content: thank you all for your answers, they helped me a lot!I made a terrible evaluation error, I work with a frequency of 50Khz and I noticed that MC33078P has a sufficient bandwidth while LM358 was not working due to its more limited bandwidth.making the AGC circuit work at 1Khz also LM358 works properly

author: Benta
author_rank: Super Contributor
timestamp: May 23, 2020, 04:53:14 pm
content: Why not just use an ON Semi NE570?Much simpler (and probably better performing).

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 23, 2020, 04:57:52 pm
content: Quote from: Benta on May 23, 2020, 04:53:14 pmNot bad.

author: salviador
author_rank: Regular Contributor
timestamp: May 24, 2020, 09:42:21 am
content: thanks for the tip I did not know this integrated NE570
Op Amp array IC - Page 1
Forum section: electronics / projects

author: fonograph
author_rank: Frequent Contributor
timestamp: August 03, 2018, 11:28:52 am
content: Is there some IC that have huge number of tiny op amps? The more the better.

author: MT
author_rank: Super Contributor
timestamp: August 03, 2018, 12:46:22 pm
content: I dare to say no since i also want tiny opamps for making 2 pole PWM filter buffers.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 03, 2018, 01:08:28 pm
content: Application-specific, very expensive arrays do exist. If you are after general purpose and low cost, it's hard to beat using cheapest jellybean quads or duals in the smallest SMD package you can find.

author: JPortici
author_rank: Super Contributor
timestamp: August 03, 2018, 01:15:03 pm
content: i'm afraid soi was able to find 8/16 channels buffer amplifiers that in reality were just common colloctor buffers. Pity.I am sure there are some strange unobtainable automotive parts but that is not of help.

author: b_force
author_rank: Super Contributor
timestamp: August 03, 2018, 01:21:30 pm
content: Well with an opamp you always need 3 connections.So the amount of pins adds up.Depending on the application a DSP would be an easier choice nowadays.

author: JPortici
author_rank: Super Contributor
timestamp: August 03, 2018, 01:24:30 pm
content: with a buffer you only need two pins. bonus if placed in a logical manner like ULN2003

author: RoGeorge
author_rank: Super Contributor
timestamp: August 03, 2018, 01:25:16 pm
content: There is something like an FPGA, but with configurable op-amps instead of configurable logic. They are called FPAA.https://en.wikipedia.org/wiki/Field-programmable_analog_array

author: fonograph
author_rank: Frequent Contributor
timestamp: August 03, 2018, 02:13:06 pm
content: Quote from: RoGeorge on August 03, 2018, 01:25:16 pmOMG YESSSSSS! Thats exactly the kind of thing I was looking for,thank you so much

author: b_force
author_rank: Super Contributor
timestamp: August 03, 2018, 02:33:42 pm
content: Quote from: RoGeorge on August 03, 2018, 01:25:16 pmGood thinking!

author: fonograph
author_rank: Frequent Contributor
timestamp: August 03, 2018, 02:41:54 pm
content: Does anybody know which FPAA can have most op amps active at same time? I would prefer to have ball grid array with gazillion bajillion metrik funktonillion pins for maximum number of active op amps at same time.

author: b_force
author_rank: Super Contributor
timestamp: August 03, 2018, 03:10:09 pm
content: Quote from: fonograph on August 03, 2018, 02:41:54 pmWhat do you actually need to do with all these opamps?

author: Benta
author_rank: Super Contributor
timestamp: August 03, 2018, 04:13:15 pm
content: The company best known for this kind of thing is Anadigm.No affiliation.

author: fonograph
author_rank: Frequent Contributor
timestamp: August 03, 2018, 05:19:16 pm
content: Quote from: b_force on August 03, 2018, 03:10:09 pmI would prefer to avoid disclosing that information.
Op-Amp Buffer into 1073 Mic Pre? - Page 1
Forum section: electronics / projects

author: lesabb
author_rank: Contributor
timestamp: January 09, 2015, 03:52:22 am
content: Hello all,I'm looking into different solid state Mic pre designs. Now I know that transformer in and out is nice and gives that "je ne sais quoi" to the 1073 (and others) but is there any reason why one could not use an op-amp buffered input (and output) on BA283 boards (1073 in and output modules)? Definitely would be cheaper, not to mention lighter if building multiple chanels...Am I out to lunch with this?L

author: dannyf
author_rank: Super Contributor
timestamp: January 09, 2015, 12:16:02 pm
content: Have you thought about using 5025a instead? I have seen people using even 60Z6 successfully here.

author: lesabb
author_rank: Contributor
timestamp: January 09, 2015, 02:37:26 pm
content: I'm quite new at this and I'm not sure what the 5025 is. Op Amp? Isn't the 60Z6 a Zener?
Op amp buffer - Page 1
Forum section: electronics / projects

author: Thomashoej
author_rank: Newbie
timestamp: January 20, 2021, 09:10:48 pm
content: Hi.I was wondering why the signal from the pot has to be buffered in this case, since the input resistance should be the same on both op-amps.Is it essential or unnecessary?Thanks

author: Gyro
author_rank: Super Contributor
timestamp: January 20, 2021, 09:24:47 pm
content: Welcome to the forum.It looks as if somebody was trying to find a use for the spare half of the opamp to me. Yes you're right, it's unnecessary.If it was me, I would use the spare opamp as a comparator to drive an 'out of compliance' indicator - monitoring the drive voltage to the gate of the Mosfet to see if it goes too close to the positive rail (ie, the circuit unable to maintain current regulation).

author: Thomashoej
author_rank: Newbie
timestamp: January 20, 2021, 09:39:36 pm
content: Thanksand thanks for the answer

author: Doctorandus_P
author_rank: Super Contributor
timestamp: January 20, 2021, 10:39:02 pm
content: I would use the extra opamp to stabilize the zener voltage.The idea is to amplify the zener voltage about 1.3x, and then feedback the output of the opamp to the current limiting resistor for the zener.It's a quite commonly used circuit and you only need 2 extra resistors.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: January 21, 2021, 02:55:04 am
content: Yes, waste of a good opamp. As above, you can increase the performance of the reference with it. You can also then adjust the reference voltage such that a standard value pot with a good turns counting dial can be used to set the current with surprising accuracy.

author: ledtester
author_rank: Super Contributor
timestamp: January 21, 2021, 09:27:57 am
content: Note that the inputs of unused op-amps should be tied to well-defined voltages:https://www.ti.com/lit/an/sboa204a/sboa204a.pdfhttps://www.maximintegrated.com/en/design/technical-documents/app-notes/1/1957.htmlSo this is a way of using the second, unneeded device.

author: Ian.M
author_rank: Super Contributor
timestamp: January 21, 2021, 10:33:45 am
content: It would make sense, if there was a potential divider between the two OPAMPs to allow a lower value current sense resistor to be used.

author: Terry Bites
author_rank: Super Contributor
timestamp: January 21, 2021, 06:02:02 pm
content: IC1a us superfluous

author: David Hess
author_rank: Super Contributor
timestamp: January 22, 2021, 04:09:29 pm
content: Sometimes a high impedance input is buffered to prevent violation of the input common mode voltage range but this does not appear to be necessary in this case. I would use the extra operational amplifier to double the drive to the power MOSFET.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: January 22, 2021, 04:46:15 pm
content: Single opamps might be even more expensive then the dual one.It is better to not have a opamp unconnected, the manual says what to do with unused opamps ( connect center volt into buffer ).I think there are people who buy only dual packages.I like to save energy and take a single package.
OP-Amp circuit problem - Page 1
Forum section: electronics / projects

author: jazzalex
author_rank: Regular Contributor
timestamp: January 17, 2014, 11:21:23 am
content: Hello all,I have a simple OP-Amp circuit, which is supposed to work as a bandpass amplifier. I designed and simulated it with qucs. The results are attached to this post (circuit and simulation).For some reason, however, it does not work properly as shown in the third attachment: I used a sine as the input waveform (yellow) and the output (green) shows significant distortions of high frequencies.Does anyone know how to debug this problem ?Thanks in advanceAlex

author: fcb
author_rank: Super Contributor
timestamp: January 17, 2014, 11:46:52 am
content: 20R as feedback resistor!50R load for an '071!Try increasing your resistors by of at least x10 (probably better at x100).

author: kg4arn
author_rank: Unknown
timestamp: January 17, 2014, 12:50:36 pm
content: fwiw. The design is unstable (oscilatting) due to the large capacitance at the neg op amp input.Try a different architecture like something from "op amps for everyone" which is free to download.

author: dannyf
author_rank: Super Contributor
timestamp: January 17, 2014, 01:31:07 pm
content: QuoteThe ac gain increases with frequency and is only modulated by the device's own gpbw.

author: jazzalex
author_rank: Regular Contributor
timestamp: January 24, 2014, 01:06:01 pm
content: Thanks for your help ! I will try to redesign the circuit and will definitely read through the OP-Amp book you mentioned above !

author: jazzalex
author_rank: Regular Contributor
timestamp: January 31, 2014, 02:09:51 pm
content: Update: I changed the 20 R resistor to 2000 R and reduced the capacity from 220 nF to 1 nF. This results in a stable circuit with almost the same S-parameter-characteristic.Thanks againAlex
op amp current sense amplifier. - Page 1
Forum section: electronics / projects

author: m3vuv
author_rank: Super Contributor
timestamp: December 21, 2018, 08:37:43 am
content: hi all,im after using an op amp as a current sense amp on a psu,30v max output,the op amps i have are jrc4558 ic's,the max supply voltage is 18v,i wanted to use them from the same power rail as the psu,obviously i cant do that,now the question is can i power it from say a lm 7824 reg?,the differential voltage is 30v max,can the voltage at the current sense resistor be higher than the op amp supply voltage?hope that makes sense,cheers m3vuv.

author: Zero999
author_rank: Super Contributor
timestamp: December 21, 2018, 09:33:55 am
content: What makes you think the JRC4558 is only rated to 18V? The data sheet says +/-22V, which is a total supply voltage of 44V.https://img.ozdisan.com/ETicaret_Dosya/408213_9227758.pdfThe maximum differential voltage rating is 18V, so make sure the voltage between the inputs stays below that and it will be fine.The common mode range doesn't include either supply rail and is specified at ±12V worst case, with a +/-15V supply, so the voltages at both input pins should be over 3V or more from either supply rail, for it to work properly. This means if the power supply voltage is 30V, the voltages at the inputs must range from 3V to 27V, in order for the op-amp to work. This could be an issue if the current sense resistor is on either rail. One way round this is to power the op-amp from the unregulated voltage and put the current sensor on the output, which will always be a few volts lower.

author: Simon
author_rank: Unknown
timestamp: December 21, 2018, 04:21:39 pm
content: Please do not post the same topic twice!
op amp current source feedback filter? - Page 1
Forum section: electronics / projects

author: SArepairman
author_rank: Frequent Contributor
timestamp: September 03, 2014, 02:03:54 am
content: A dual op amp current source (buffered high impedance howland current pump) is driving a wire with a current going to a sensor. This wire runs in parallel with audio frequency (of 100mAish rms power) lines for about a meter.Does it make sense to put a sallen key filter in the feedback path after the howland current pump feedback buffer?I saw this in an app note before. Will this sort of current source turn coupled noise into current?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 03, 2014, 02:17:40 am
content: "Audio frequency" = < 20kHz BW, or not many times more than that.1m of most any kind of cable isn't going to be more than ~300pF, or more than 26kohms reactance (or not many times below that).So, if you current source is much better than 26kohms, you're wasting your time -- or alternately, if the sensor can't tolerate under 26kohms of compliance or crosstalk. (Which means, for example, a Howland CCS built with 1M 5% resistors will still have a worst case good enough for present purposes, if I'm estimating that right.)What is this, current bias for a voltage on the sensor?Tim

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: September 03, 2014, 03:25:14 pm
content: Howland can be a poor choice for a regulated unipolar current source - a fet or a bjt (with base current compensation if needed) can have higher output Z to higher frequency, only one op amp needed for adding accuracy to the transistor ccsand you shouldn't in general "add a filter" to a feedback connection - feedback loop performance has to be designed for
OP amp data - Page 1
Forum section: electronics / projects

author: andy3055
author_rank: Super Contributor
timestamp: May 06, 2021, 04:42:46 pm
content: For anyone interested, here is a link to download OP amp guide published by Mouser:https://emea.info.mouser.com/opamp-reference?utm_source=ietuk&utm_medium=newsletter&utm_campaign=mouser-opamp-reference?cid=nltext&pid=iet&utm_content=1x1&utm_id=448904?cid=nltext&pid=iet&dclid=COG0-rq_tfACFWQO5wodcnUO3gWell, it is just a basic 1 page document. Not a whole lot there! Sorry about that.

author: ledtester
author_rank: Super Contributor
timestamp: May 06, 2021, 05:04:39 pm
content: Note this requires email registration and redirection through a lot of urls which are flagged by uBlock Origin.The PDF is only a single page and only contains diagrams of 8 basic opamp configurations with no discussion of them.

author: ledtester
author_rank: Super Contributor
timestamp: May 06, 2021, 05:06:59 pm
content: In case people aren't aware of it, TI's 460 page "Op Amps For Everyone" is an excellent reference for op amp design.

author: rdl
author_rank: Super Contributor
timestamp: May 06, 2021, 05:21:04 pm
content: The site appears valid and may be flagged in error by the "Easy Privacy" filter. But the registration requirement and how it is implemented smells funny. I couldn't access it even when logged in to the main Mouser site.Code:https://emea.info.mouser.com/

author: gamalot
author_rank: Super Contributor
timestamp: May 06, 2021, 05:23:15 pm
content: Quote from: ledtester on May 06, 2021, 05:06:59 pmThank you! I also found the third edition, it has 600 pages.http://index-of.es/z0ro-Repository-2/Cyber/02%20-%20Electronic%20Engineering/Op%20Amps%20For%20Everyone,%20third%20edition%202009%20(Texas%20Instrument).pdf

author: andy3055
author_rank: Super Contributor
timestamp: May 06, 2021, 07:08:56 pm
content: Thanks for the replies. The link is legit. It came from my IEE UK membership email. I would not post otherwise. But I was also disappointed at the 1 page doc. Expected much more.
op amp feedback values - Page 1
Forum section: electronics / projects

author: raff5184
author_rank: Regular Contributor
timestamp: February 27, 2017, 11:25:24 pm
content: Hi I am building this evaluation board:http://www.analog.com/media/en/technical-documentation/user-guides/UG-755.pdfHow do I design CFand CLin the fist circuit on page 3? Is there a formula?Thank you

author: tpowell1830
author_rank: Frequent Contributor
timestamp: February 28, 2017, 01:37:16 am
content: It depends on how you want to use the Op Amp. if you are just using as an Op amp with gain, you don;t really need Cf and CL. How do you plan to use it? If you want to create an oscillator, there is one formula and if you just want to amplify a signal there is another. Did you get any other info with the device? I don;t see the specs. Look at Dave's video on setting Op amp gains etc or this one from w2aew that I like.

author: danadak
author_rank: Super Contributor
timestamp: February 28, 2017, 02:23:41 am
content: This might help -http://www.ti.com/lit/an/sloa020a/sloa020a.pdfRegards, Dana.

author: raff5184
author_rank: Regular Contributor
timestamp: February 28, 2017, 03:03:48 am
content: I just plan to use it as a power amplifier, to increase the input voltage or power in general.I found the formula CL= 1/(2*pi*R*f) , but apparently I don't need it since, if I am correct, CLis used to create a low-pass filter(?)

author: tpowell1830
author_rank: Frequent Contributor
timestamp: February 28, 2017, 03:12:28 am
content: Quote from: raff5184 on February 28, 2017, 03:03:48 amYes, a low pass filter. I think that the drawing is showing that all of those features are available on the board, but you don't necessarily need them. If you want to create a high gain amplifier, there is a method to choosing the components and you can do it with a much smaller component count than is shown.
Op-amp for current sensing - Page 1
Forum section: electronics / projects

author: steve30
author_rank: Frequent Contributor
timestamp: May 06, 2013, 01:36:35 pm
content: I am building a Lab PSU, see the schematic attached. It has current limiting. The current is sensed by the 1R resistor and is measured by a differential amp circuit, which uses an LM324 op-amp.It seems to work fine in my testing. But I was wondering, is an LM324 ideal for this, or would anything else be more suitable, for example, a dedicated differential amp IC?Thanks.steve30.

author: electros6
author_rank: Regular Contributor
timestamp: May 06, 2013, 01:41:37 pm
content: lm324 is enough for this application. It gives the same result as precision opamp

author: digsys
author_rank: Unknown
timestamp: May 06, 2013, 02:08:24 pm
content: Linear Technologies, INA198 ... series is excellent for this type of thing. I rarely use anything else.Fixed x100, x50, x20 up to 80V Sense. Excellent accuracy and linearity. Just so easy to use and NO surprises !!

author: Ghydda
author_rank: Regular Contributor
timestamp: May 06, 2013, 02:09:27 pm
content: Quote from: electros6 on May 06, 2013, 01:41:37 pmTrue. LM324 should be adequate in this application.But the transistor coupling following the 2nd opamp - which limit the output voltage of the LM317 - is going to be be a real troublemaker.The trouble is that the gain of the current sensing system will be really really high (open loop gain of the 2nd LM324 times hfe from the transistor) and really temperature dependent to bootFind another way is my advice.

author: poorchava
author_rank: Super Contributor
timestamp: May 06, 2013, 03:58:25 pm
content: OP07

author: steve30
author_rank: Frequent Contributor
timestamp: May 06, 2013, 07:06:10 pm
content: Thanks for the suggestions. I might have a play with other chips at a later date.I don't see why the transistor would be a problem? It seems to work fine.Only issue I really have is the comparator stage, where the op-amp compares the measured current with the set current. The waveforms I get out of this are really weired. Not really sure if they should be or not as the circuit does actually seem to work fine.
Op amp gentle phase fold? - Page 1
Forum section: electronics / projects

author: MT
author_rank: Super Contributor
timestamp: October 14, 2017, 11:20:08 pm
content: The CA3260 and 3160 have the peculiar feature gentle phase folding while most opamps abruptly phase reverse.is there any other opamp that does the same as CA3160?

author: Benta
author_rank: Super Contributor
timestamp: October 15, 2017, 08:15:12 am
content: Do you mean that the output does not phase reverse when the input goes below the negative rail?Quite a lot of opamps have this, I've seen several from NSC and TI. It has to be specifically mentioned in the datasheet.

author: MT
author_rank: Super Contributor
timestamp: October 15, 2017, 06:48:34 pm
content: Unipolar supply.Phase reversalPhase folding:

author: Audioguru
author_rank: Super Contributor
timestamp: October 15, 2017, 09:11:44 pm
content: The datasheet for the CA3160 says thatit does not reverse the phasewhen its input goes 7.5V below ground when it has only a positive 15V supply.Its common mode input voltage range is -0.5V to +12V with a single +15V supply.

author: Benta
author_rank: Super Contributor
timestamp: October 15, 2017, 09:17:48 pm
content: This is all fine, but I still don't understand what the question is.Perhaps MT could enlighten us?

author: mikerj
author_rank: Super Contributor
timestamp: October 16, 2017, 11:13:52 am
content: Quote from: Benta on October 15, 2017, 09:17:48 pmSeems pretty obvious, he is asking if there are any other op-amps that display the same phase characteristics as the CA3260 when the common mode range is exceeded. I don't know of any myself.

author: MT
author_rank: Super Contributor
timestamp: October 16, 2017, 01:44:01 pm
content: Mikerj nail'ed it!There are some old PNP amps that also folds but does it ugly. Phase folding is a natural transistor phenomenon.
op amp high speed buffer  - Page 1
Forum section: electronics / projects

author: Alex QW
author_rank: Contributor
timestamp: October 10, 2023, 07:52:28 am
content: Hi guys,Do you know any alternative component that can be replaced for this high-speed buffer OPA633KP Texas Instruments?https://my.rs-online.com/web/p/video-amplifiers-ics/0647586Thanks

author: moffy
author_rank: Super Contributor
timestamp: October 10, 2023, 08:03:15 am
content: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1127779/opa633-replacement-options
Op-Amp Idle Current - Page 1
Forum section: electronics / projects

author: w3amd
author_rank: Regular Contributor
timestamp: December 28, 2015, 08:12:16 pm
content: Hi all,I'm trying to understand something in the op-amp datasheets. For idle or quiescent current datasheets give a value of typical and maximum current.For a dual rail supply of +12,-12 does this mean each side of the power rail is using this amount of current?Should I be dividing this current value by 2 if a dual supply is used?I'm trying to calculate idle power used of each op-ampTIA,John

author: tszaboo
author_rank: Super Contributor
timestamp: December 28, 2015, 08:17:07 pm
content: The same current flows from the positive supply to the negative supply. The amp has no concept of ground. Also, no dividing by two, if anything, you have to double it to get the absolute value.The q. current will be dependent on the temperature and the supply voltage, with some spread from part to part.

author: ajb
author_rank: Super Contributor
timestamp: December 28, 2015, 08:20:58 pm
content: The op amp has no idea if it's connected to a dual rail or single supply. Iq flows from Vdd through the op amp and into Vss, so quiescent power dissipated by the op amp will be (Vdd-Vss)*Iq, regardless of whether or not Vss==Gnd. So yes, both the -12V supply *and* the +12V supply need to supply the full quiescent current, but only half of the quiescentpower, assuming a symmetrical split supply.

author: TimFox
author_rank: Super Contributor
timestamp: December 29, 2015, 09:55:45 pm
content: As stated above, the quiescent current flows from the positive supply terminal through the device to the negative supply terminal.Any current delivered into the circuit's load (positive or negative) will be in addition to the quiescent current, but will flow from one or the other supply terminal, as required.
Op amp input voltage - Page 1
Forum section: electronics / projects

author: PatrickJC
author_rank: Newbie
timestamp: April 15, 2025, 02:16:23 pm
content: Hi,I am working on a project where I need to get a rough estimate of a 12V or 24V lead acid battery in construction vehicles. I can't use a fuel gauge or battery monitor because the battery will never be fully depleted and fully charged over multiple cycles. I decided to use inverting op amps to reduce the voltage so the ADC on the MCU I'm using can report the voltage. I know this will not be an accurate representation of the charge remaining on the battery. I just need a rough estimate while the vehicle is turned off for a long period of time.For the op amp it is easier, more cost effective and more space efficient to use +5V and -5V for the supply. Since the max input voltage to the negative input could be +28V to the negative input I'm using a voltage divider to reduce the input below +5V.My question is, is it actually necessary to use the voltage divider to reduce the voltage? I know for most op amp the input voltage cannot excided the supply voltage. But where the positive input is grounded and op amps try and make the voltage of both the input terminals the same, will the input voltage on the negative terminal be almost 0V? Or am I misunderstanding the fundamentals of op amps?Thanks for the help!
Op-Amp integrator - Advice please... - Page 1
Forum section: electronics / projects

author: AndersJ
author_rank: Frequent Contributor
timestamp: April 23, 2021, 10:58:40 am
content: I have a integrator as shown in the picture below.Red curve: 5V digital input.Green curve: Integrator output.There is a delay before the integration starts.The delay is longer for the larger RC.What causes the delay?

author: David Hess
author_rank: Super Contributor
timestamp: April 23, 2021, 12:06:36 pm
content: Under normal conditions delay is caused by the limited bandwidth of the operational amplifier, which is especially problematic in an integrator because the operational amplifier must be compensated for unity gain which limits the bandwidth.In your example however, there is also delay caused by recovery from saturation.

author: AndersJ
author_rank: Frequent Contributor
timestamp: April 23, 2021, 02:19:50 pm
content: Oops, bad schematic.The diode is NOT shorted.Assuming my issue is saturation,would a 4,5V diode clamp across C reduce/eliminate saturation?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 23, 2021, 03:09:12 pm
content: Clamping accross the cap could suppress the saturation. However with 5 V supply and the virtual ground at 2.5 V it would need more like a 2.4 V diode or similar.

author: AndersJ
author_rank: Frequent Contributor
timestamp: April 23, 2021, 03:49:24 pm
content: Yes,virtual ground, of course.I was thinking GND, when I suggested 4,5V.I just tried this, with 2 x (yellow LED + 1N4148).Almost full swing, and no delay.Will the saturation harm the op-amp,shortening its life,or have other other negative effects?

author: David Hess
author_rank: Super Contributor
timestamp: April 24, 2021, 06:33:16 pm
content: Quote from: AndersJ on April 23, 2021, 03:49:24 pmThere is no risk of damage. Saturation creates recovery time and may cause increased supply current which may or may not be acceptable.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 26, 2021, 06:46:23 pm
content: When is an integrator not an integrator?...Saturation of the output, means the op-amp can no longer keep up with the input, and the linearity assumption used in the integrator derivation is broken. Input voltages are no longer equal, and that is the hint as to where the extra time is going.To minimize windup, clamp the inputs together with a pair of diodes. To eliminate it entirely, use a transconductance amp (with sharp, well behaved saturation!) into a capacitor, then a buffer.Tim
Op-amp max current output vs frequency - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: January 22, 2020, 03:27:27 am
content: Hi,does op-amp current vary depending on frequency? I'm thinking most likely the max current output decreasing as frequency increases perhaps, due to losses and parassitics? I googled it and looked on few datasheets but could not find any such graph/parameter.Thanks

author: profdc9
author_rank: Frequent Contributor
timestamp: January 22, 2020, 03:37:26 am
content: What you want to look at is slew rate. Slew rate is the maximum change to the output of the op-amp in volts/second. So for example, if the op-amp is driving a 100 ohm load, and the slew rate is 5 volts/microsecond, then the change in current is 50 mA/microsecond. So for example, for an output at 1 MHz/(2 pi) or about 159 kHz, the maximum oscillation amplitude in current is going to be 50 mA.

author: magic
author_rank: Super Contributor
timestamp: January 22, 2020, 09:08:48 am
content: There is a current slew rate too. If nothing else, the slew rate times output stage transconductance is the limitand it may be worse due to input capacitance of the output transistors and limited drive current available from the gain stage.But if it's not specified then it probably is not a problem in any reasonable application and the usual voltage slew rate is the limit, as outlined above. Unreasonable applications where this may not apply involve: driving very high current at very high frequency into very low impedance load.

author: Vovk_Z
author_rank: Super Contributor
timestamp: January 22, 2020, 12:03:09 pm
content: Quote from: ricko_uk on January 22, 2020, 03:27:27 amMax output voltage usually will decrease with frequency, but current not so much. Actually we can think that it doesn't change.

author: David Hess
author_rank: Super Contributor
timestamp: January 22, 2020, 08:25:09 pm
content: It would be interesting to test. Output current slew rate will be primary limited by voltage slew rate into the output load. Voltage slew rate is limited by the compensation. Current gain of the output transistors drops with frequency however that is way beyond the other limits.

author: magic
author_rank: Super Contributor
timestamp: January 23, 2020, 08:33:08 am
content: On second thought, there is a much more reliable and predictable limit to output stage transconductance than storage effect or parasitics: the output protection resistors.Take the classic NE5532 with its 15Ω. You aren't getting more than 70mA/V out of that thing. Given 8V/µs voltage slew rate, that's 560mA/µs current slew rate into a dead short. So at 5MHz it's limited to 18mA peak into a short, even though normally it could do twice more. Add 15Ω of external load and the limit becomes 9mA at 5MHz or 18mA at 2.5MHz.But the above example also shows that one needs to go to quite extreme lengths to encounter this problemOr use RC4558. According to Raytheon, its output resistor is 120ΩBut I'm not sure if it's not a typo and I felt like using such a lousy opamp for this example would be cheating
OP-AMP Missing-GND rail protection(for failsafe applications ) - Page 1
Forum section: electronics / projects

author: electronx
author_rank: Regular Contributor
timestamp: November 15, 2022, 05:59:15 am
content: hi, I have designed a howland current source using tlv9351. From the power rails of the opamp, the gnd pin is externally connected to the connector. When the gnd pin is removed, the IC starts to heat up and breaks down.The troublesome part of the job is that when the gnd pin is removed, the opamp internally moves the V- pin to the V+ pin. How can I prevent this situation? . How can I set up a system that will disable the opamp and prevent it from burning when GND is removed?An important consideration is how the output will behave if we lose ground connection "physically". In terms of safety, we also need to evaluate this possibility. (failsafe design ) .so Our case is the floating GND state.

author: jonpaul
author_rank: Super Contributor
timestamp: November 15, 2022, 07:35:00 am
content: poor engineering practicesimple solution use connector with shell at ground/ earth that mates before other pins.You will not protect the opamp against such bizarre abuseJon

author: Terry Bites
author_rank: Super Contributor
timestamp: November 15, 2022, 05:21:28 pm
content: You have uncontrolled current flow through the opamps ouput stage.The only place the opamp can pull high current is via T1.I'm guessing that you only need a few mA of current which the opamp is able to manage without T1.Look at Fig 7.8 in the datasheet and work out where excess current might flow.I'd start by putting a 10k resistor in series with T1's base.Then I'd consider a better CCS topolgy. Of which there are many.

author: electronx
author_rank: Regular Contributor
timestamp: November 21, 2022, 11:57:14 am
content: thanks for your feedbacks .It means I have to change the design topology. Actually, I need a voltage-controlled current source. So I need a voltage-controlled current source that protects itself when gnd is disconnected(missing GND rail protection(failsafe protection ) ) and specs are 1-5V input range and 4mA-20mA output range . Is there a reference design or IC that can provide this feature?

author: Terry Bites
author_rank: Super Contributor
timestamp: November 21, 2022, 04:29:02 pm
content: There are specific ics for this egwww.ti.com/amplifier-circuit/special-function/4-20ma-signal-conditioners/overview.html?keyMatch=CURRENT%20LOOP%20TRANSMITTERSorwww.analog.com/en/product-category/4-20-ma.htmlThese industrial ICs are designed to be pretty bomb proof. It's not hard to cook up your own loop XMTR, see attached. You may not need to go crazy with precision parts, its up to you to balance cost and effectiveness.You may find this interesting:training.ti.com/ti-precision-labs-op-amps-current-loop-transmitters-basics-analog-input-3-wire-4-20ma-current-loopThe Howland source is more of a textbook circuit. Its a pain in the arse because of the requirements for matched resistors and opamp CM range. It has very limted output compliance and you'll rarely see it used in practice. In gerneral current sources are a pain, believe me........
OP-AMP output voltage swing - Page 1
Forum section: electronics / projects

author: mattko
author_rank: Contributor
timestamp: June 27, 2018, 10:00:13 am
content: Hello!In this document:http://www.ti.com/lit/an/sloa011/sloa011.pdfPage 29. It is stated that maximum output voltage is VO <= +VCC – VR1 – VBEQ6 – VSATQ6.I don't understand why it is not just VO <= +VCC – VR1 – VBEQ6 OR VO <= +VCC – VR1 – VSATQ6.Why do they count the base-emitter drop and Vce sat drop?The same goes for minimum output voltage.Thanks

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 27, 2018, 10:38:33 am
content: I also do not understand this.I also think that the current source for the base of the transistors would need some voltage drop to work properly. Stating that Vbq6 equals Vcc seems ... incomplete.But on a practical term it would not matter much. opamps with this bipolar output stage can not output voltages which is within 1V5 to 2V of either supply rails and this is usually given in the datasheets.Picture is screenshot of page 29 of sloa011.pdf

author: RobK_NL
author_rank: Frequent Contributor
timestamp: June 27, 2018, 11:08:16 am
content: Quote from: Doctorandus_P on June 27, 2018, 10:38:33 amBut that is not what they say, is it?You are most likely right that Vbq6 will be lower than Vcc, but any which way you turn it, Vbq6 can never behigherthan Vcc.For the transistor to conduct, Vbq6 must be at least VBEQ6higher than the voltage at the emitter of Q6 (Veq6 for short). So it follows that Veq6 cannot be higher than Vcc-VBEQ6.With Q6 fully saturated, there will be a voltage drop of VCEsatacross it, which also detracts from the maximum output. This then gives us VO <= +VCC - VBEQ6 – VSATQ6

author: mattko
author_rank: Contributor
timestamp: June 27, 2018, 01:57:13 pm
content: Quote from: RobK_NL on June 27, 2018, 11:08:16 am

author: David Hess
author_rank: Super Contributor
timestamp: June 28, 2018, 02:57:36 am
content: Quote from: mattko on June 27, 2018, 10:00:13 amI do not know either; lately Texas Instruments has been producing some pretty poor documentation.Vce saturation is less than Vbe forward so the later is all that matters. The PNP current source has its own Vce saturation and that does add to the output but it is not shown in detail in the schematic. So the output is Vcc - Vce saturation of PNP - Vbe forward of NPN - VR1.
op-amp prototyping circuit - Page 1
Forum section: electronics / projects

author: DedeHai
author_rank: Newbie
timestamp: June 05, 2017, 03:19:58 pm
content: Hey everyone,I wanted to share my PCB design I call 'universal op-amp circuit' and as an engineer myself I thought this might be of use to others.The design is intended to make testing of op-amp circuits a whole lot easier and less messy. It supports SO8 dual opamp and SOT23-5 single opamp with the standard pinout like the LM358 (SO8) or LM321 (SOT23-5). There is some more info available on my blog:https://bashtelorofscience.wordpress.com/2017/06/05/universal-op-amp-circuit-pcb/I also shared the design in the shop at dirtypcbs.com if you would like to order it (15$ for 40 boards, shipping included!). Their quality is not great (not that they claim that it is) but it is good enough for some tests.To Dave: if you read this and approve, leave a reply and I will send a few boards your way ASAP.
Op Amp Selection for Sigma Delta Modulator - Page 1
Forum section: electronics / projects

author: kiran_shrestha
author_rank: Regular Contributor
timestamp: April 27, 2014, 09:35:27 am
content: Hi, I am desinging a Class D amplifier and have decided to use the sigma delta modulator but i am confused choosing the right op amp for this and i am using 300Khz as sampling frequency. Plz help..
Op amp stability problem wandering and shifting - Page 1
Forum section: electronics / projects

author: R_G_B_
author_rank: Frequent Contributor
timestamp: March 31, 2014, 03:50:30 pm
content: I have an opam stability problem as follows:At low frequency im getting base line wandering seems to be oscillation of some sort the amplitude seem to also increase before settling and wandering on the oscilloscope. Also when you change the voltage sensitivity of the scope the waveform shifts up or down on a D.C level. I tried using a small compensation capacitor across the feed back resistor not much happens. I also tried filtering the supply with small caps nothing happens. Im running a tracking d.c supply on the opamp.I have narrowed it down to a mostly low frequency problem because at high frequency I see a stable waveform trace. However the waveform shifts up or down on a D.C level when the scope voltage sensitivity is adjusted. Has anyone had such a problem? what can be done to fix it?Thanks for your help.

author: nickm
author_rank: Regular Contributor
timestamp: April 01, 2014, 02:47:43 am
content: Post schematic. Could be a variety of things such as temperature, noise, etc. What kind of scope, probes, etc? The scope should present a constant load and the outside world should have no knowledge of what attenuation your scope is set at.
Op amp substitute JRC / CA4580 with NE5532 (Bonus: AI slop) - Page 1
Forum section: electronics / projects

author: John B
author_rank: Frequent Contributor
timestamp: August 18, 2025, 02:42:37 am
content: I'm repairing a Behringer mixer which appears to have a blown output opamp. All the opamps are Cool Audio 4580, which looks to be a SE Asian substitute for the JRC4580?Unfortunately I don't have any of those in the parts draw, but plenty of NE5532 and TL072. The NE5532 has higher input bias current over the 4580 (200nA vs 100nA), and a higher slew rate (9V/us vs 5V/us). It looks like it should work though in order to get it working again, for about 50c worth of parts. Thoughts?For the bonus content, I asked Brave's AI. Clearly it's been huffing some audiophile stacked opamp smoke:Quote

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: August 18, 2025, 03:58:30 am
content: Typical AI brain fart. Verbose reply with limited information.Having said this….Would make good reading to ask the exact same question to other AI engines and compare the differences in the replies.With respect to the different opamp question, how do they compare with respect to offset voltage? Would only be important for DC coupled circuits, though.

author: John B
author_rank: Frequent Contributor
timestamp: August 18, 2025, 04:46:31 am
content: Same 0.5mV typical value for both. Yes, being an AC coupled circuit, it looked like DC offsets would be the only circuit differences, which would be irrelevant after the AC coupling caps anyways.I went ahead an tried the NE5532, and appears to work perfectly fine. The old CA4580 had a ton of distortion on the 2nd output and output 1 was basically pegged to the negative rail + ~0.6V

author: magic
author_rank: Super Contributor
timestamp: August 18, 2025, 05:45:58 am
content: NJM4580 has relatively large output current capability, so they may have used it for this reason (besides cost obviously). It can sort-of drive low impedance headphones directly, at least until it blows because it has no active current limiting IIRC.editIs NE5532 down to 50c today? If you got it from AliExpress, it's very likely fake.

author: John B
author_rank: Frequent Contributor
timestamp: August 18, 2025, 06:19:00 am
content: Quote from: magic on August 18, 2025, 05:45:58 amThey are SOIC package ones from TI which I got from LCSC a while back. Theyre quite cheap sitting currently at 10-15c USD in small quantities.In AUD, factoring in currency conversion fees and postage fees brings it up somewhere under 50c.