hybridfree/eevblog-posts huggingface dataset:
Op amp rectifier : transfer function and output impedance - Page 1
Forum section: electronics / beginners

author: Ryl
author_rank: Contributor
timestamp: March 27, 2012, 03:23:26 pm
content: Hello guys,I'm working on an EE student project which uses a rectifier to keep the peak value of a sine wave.You can find a PSpice pic of the schematics below (Ve is the input (1kHz), Vs is the output).I really have problems to analyse this pic. It is quite easy when I replace the diode by a short (and forget about the capacitor for now), then I just have Vs = (2+R3/10k)Ve (the potentiometer R3 gives a variable gain) by considering the op amp is ideal. Until now, it is okay.When Ve is positive, the diode is on and the upper relation between Ve and Vs is correct, knowing that the 0.6V voltage drop accross the diode is compensated by the op amp.When Ve is negative, the diode is off and the op-amp saturates at -Vsat behind the diode.Until now, is it correct ?Everything becomes more complicated when we put on the capacitor. It works perfectly to keep the peak value but I don't understand everything yet.When the diode is on, the time constant should be very small, isn't it ? The output impedance of the op amp should be near zero, so the time constant tc = RC is very small, right ?And when the diode is off, all resistors in the feedback loop (R1, R2 and R3) come in the time constant and tc becomes high, isn't it ?Well, then why isn't the capacitor just following the signal when it is positive ? And stay at zero when it is down ?I'm sure I'm missing something simple, but I don't know what...And, when the time comes to find the total transfer function Vs/Ve (for both cases when the diode is on and off), I'm completely lost.Just the same when it comes to find output impedance...Hope I expressed myself clearly (and my English wasn't too bad).Any help would be greatly appreciated.Thanks a lot,Ryl

author: Unknown
author_rank: Unknown
timestamp: March 27, 2012, 07:23:09 pm
content: The diode will only conduct if the anode is ~0.6V more positive than the cathode (not than ground, since the output is not grounded), so the op-amp will never sink current, only source. The voltage across the cap should follow the op-amp on rising slopes, but since the discharge of the cap is very slow, the voltage won't decrease as the signal from the op-amp decreases. At this point, the diode becomes reverse-biased until the cap is discharged through R1+R2+R3.
Op Amp SOA and output current - Page 1
Forum section: electronics / beginners

author: Jwillis
author_rank: Super Contributor
timestamp: June 18, 2019, 05:20:28 am
content: I hate to bring this circuit up yet again.But I've been working on the circuit of the infamous 0-30v 0-3A Power supply with some modifications.I'm using the OPA445 Op Amp and so far have made successful progress in the Voltage and Current control. So far I have 0-32 volts and 0- 2.7 Amps with a 24 volt AC source .I'm not concerned about temperature drift of the zeners I've used at this time.I eventually want to increase the voltage to a 50V output so other changes will be required for better regulation.I want to jack up the amperage but I also don't want to overwork the op amps. So when determining the Vs (Voltage source) is the the additive voltage to both positive and negative Supply? By this I men, theirs 33.5 volts to the positive rail and - 16.5 volts to the negative rail so the total voltage would be 50 Volts? And the Vo (Voltage out) is 0-32Volts. So I would read the current SOA (Vs - Vo) As 50 volts maximum which would give me around 1 mA Safely at the out put?Would that be correct?https://www.ti.com/lit/ds/symlink/opa445.pdf

author: magic
author_rank: Super Contributor
timestamp: June 18, 2019, 07:57:57 am
content: Yes, it's correct, at ambient temperature of 120°C, whatever that means. At lower temperature more is permissible.Also, the datasheet is wrong. It's not |Vo|-|Vs| but |Vo-Vs|, where Vs is the supply rail which supplies current to the output. So V+ for sourcing and V- for sinking. It can make a difference if supplies aren't symmetric or if you drive a load referenced to the opposite supply rail rather than ground.Wait, no. It's not entirely correct. It's only correct if supply-output differential is at its maximum. If you drive positive current at 10V below positive supply, you only are concerned about current limit for |Vo-Vs|=10V. If you drive negative current at 10V below positive supply, then |Vo-Vs|=40V.

author: Zero999
author_rank: Super Contributor
timestamp: June 18, 2019, 08:31:58 am
content: Is there already a thread on this? If so, it would have been better to simply continue it, rather than creating a new one, so we can see the schematic. Please post a link., otherwise, please post the schematic here.You shouldn't worry about the op-amp, which probably won't have to output much current. The output transistors are where most of the power dissipation will be. For 50V, a transformer tap switching arrangement should be used, to minimise the power dissipation in the output transistors.

author: Jwillis
author_rank: Super Contributor
timestamp: June 19, 2019, 08:08:58 am
content: Quote from: Zero999 on June 18, 2019, 08:31:58 amThanks for the reply. I'm relatively new to op amps and I was simply asking if I as understanding the Data sheet correctly and saw no point in presenting a schematic at this time . This project has an on going evolution which includes transformer changes.I imagine by the time I'm finished it won't look anything like the original schematic.But i do appreciate the help.
Op Amp -Split rail w/ virtual ground for Car Audio... - Page 1
Forum section: electronics / beginners

author: Shredhead
author_rank: Regular Contributor
timestamp: January 29, 2021, 01:50:57 am
content: I know how virtual grounds work for using op amps with single supplies... for example:But in car audio, your ground is referenced to the negative terminal of the 12V battery. You can't do a virtual ground because the receiver and amplifier would be ground referenced to the virtual -6v rail.Anyone know a cheap and nasty way to use an op amp in car audio's signal chain from the car's single supply?

author: ledtester
author_rank: Super Contributor
timestamp: January 29, 2021, 02:23:34 am
content: What exactly do you want to do?You can move the "ground" for your audio processing to 6V (half the battery voltage). You place capacitors at the input and output to decouple it from the surrounding circuitry.

author: Shredhead
author_rank: Regular Contributor
timestamp: January 29, 2021, 03:55:20 am
content: I know. The car's audio equipment consists of a player and an amplifier. These units are interconnected with RCA cables and the shield is ground referenced at the battery's 0v. When the RCA is connected to the op amp and the op amp's ground is referenced at the battery's 6v... there will be a big problem when you send that signal to the amplifier. DC offset that will cook the amp and driver. Am I making sense?

author: ledtester
author_rank: Super Contributor
timestamp: January 29, 2021, 04:18:08 am
content: Maybe I shouldn't have used the term "decouple". You put a capacitor in series with the input/output - sometimes its called a "DC blocking capacitor" or "AC coupling". It removes the DC bias from a signal. You can then shift the DC bias to wherever you want for your op-amp.For instance, in this schematic C1 is the ac coupling capacitor and R1,R2 sets the new DC bias point:https://reference.wolfram.com/language/example/TransistorAmplifierCircuit.html

author: AlfBaz
author_rank: Super Contributor
timestamp: January 29, 2021, 05:23:52 am
content: Quote from: Shredhead on January 29, 2021, 01:50:57 amYep DC blocking capacitors on the input and output. They isolate DC biases within the amplifier from getting out. You don't want an AC signal riding on a DC voltage running through the speakers either
Op Amp Square Wave Generator - Help - Page 1
Forum section: electronics / beginners

author: AustinTxBob
author_rank: Contributor
timestamp: April 19, 2016, 03:16:48 am
content: I'm sure I am doing something wrong here. I've tried a couple of different op amps and a few different schematics and I cannot get any kind of oscillation. Right now I have a mcp6002 on the board with the value of the components shown in the other pic. I'm probing between ground and the output channel of the amp. Any help would be appreciated. Thanks!

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: April 19, 2016, 06:22:37 am
content: What power arrangement do you have? What voltages?If you have single supply with negative power pin of the op-amp grounded then the answer is simple. There is a resistor missing between the non-inverting input of the op-amp to power. It should be the same as R1. This will bias the input up midway to VCC to allow the inverting input room above and below it so it will switch.If you have bipolar supplies then I dont know...what else can you tell us about the environment.

author: starphot
author_rank: Contributor
timestamp: April 19, 2016, 07:06:12 am
content: Here's the op-amp basic square wave generator I took out of an app manual and tried it out for you using a TL082. Yes, you are missing some things. Single supply, your MCP6002 has a range of 1.8 to 6volts on the supply. About 1.7 KHz with components shown.Joe

author: AustinTxBob
author_rank: Contributor
timestamp: April 20, 2016, 03:52:17 am
content: Thank you very much.It makes sense to me now as to how it works as well.

author: alexanderbrevig
author_rank: Frequent Contributor
timestamp: April 20, 2016, 09:09:53 am
content: relevanthttps://www.eevblog.com/forum/beginners/op-amp-square-waves/
Op amp supply drawing large current.  - Page 1
Forum section: electronics / beginners

author: Joe_echo
author_rank: Contributor
timestamp: October 03, 2023, 05:53:05 pm
content: I have some tl074cn chips that I'm experimenting with and trying to refresh my memory on their operation.I have them hooked up to a single supply rail with 12v and ground which I believe should work, however the supply is drawing a large amount of current almost like a short circuit.Am I being a muppet and missing something vital?

author: Manul
author_rank: Super Contributor
timestamp: October 03, 2023, 06:55:07 pm
content: Obviously something is very wrong. Have you double checked the pinout? Can you post schematic?

author: Joe_echo
author_rank: Contributor
timestamp: October 03, 2023, 07:19:13 pm
content: I have checked the pinout several times just to make sure its not me.Here is the schematic

author: Manul
author_rank: Super Contributor
timestamp: October 03, 2023, 07:29:58 pm
content: Quote from: Joe_echo on October 03, 2023, 05:53:05 pmGenerally it would be better if you would give numbers, no epithets, but I assume you meanreallyhigh current like 1A or 3A. In that case I can only suggest to double check pinout again and try another (new) IC. Current one might be already irreversibly damaged.

author: Kim Christensen
author_rank: Super Contributor
timestamp: October 03, 2023, 07:35:05 pm
content: Quote from: Joe_echo on October 03, 2023, 07:19:13 pmBut whatisthe pinout? Your schematic doesn't show it.It should be something like this:

author: magic
author_rank: Super Contributor
timestamp: October 03, 2023, 07:37:45 pm
content: The schematic is sensible.If the circuit draws more than a few mA, something is clearly not the way you think.Wrong pinout.Damaged chip.Wrong part (maybe fake chip?).Reversed PSU.Bad PSU ammeter....

author: Joe_echo
author_rank: Contributor
timestamp: October 03, 2023, 07:40:16 pm
content: Sorry, yes the pinout of my device matches. Vcc= pin 4, Vee= pin 11.I believe they maybe fake ICs.

author: Joe_echo
author_rank: Contributor
timestamp: October 03, 2023, 07:40:56 pm
content: Yes, 2amp was drawn before my OCP kicked in.

author: magic
author_rank: Super Contributor
timestamp: October 03, 2023, 07:43:54 pm
content: Any pictures of the chips and/or the exact test setup?
Op-amp; switching between non-inverting and differential amplifiers on the fly - Page 1
Forum section: electronics / beginners

author: Jhonyrod
author_rank: Newbie
timestamp: September 22, 2015, 08:53:31 pm
content: Hello! I want to build a microphone preamp, mainly for my computer, but I also want to be able to use it with other equipment if I need to. I'm not talking about those cheap PC mics, I'm talking about proper mics with a balanced differential signal output.I've been working on the design for a while now, but I've got stuck in a couple of places. The matter at hand is that I want to use a single OPA2134 (dual audio op-amp) to either amplify "both" signals (hot and cold) or recombine them as a mono output, selecting between those two options with a flick of a switch. I plan on using analogue multiplexers for that effect but I'm not sure how I need to wire the op-amp to be able to switch between modes.I also want to add later a phantom power option (I was fiddling with that, that's why you see a 60V input) and maybe even a USB ADC, but first things first.Here's an screenshot of what I've got so far:S1 on that schematic switches the cold input between the op-amps and S2 grounds the non-inverting input of U1A when it's not in use.I haven't added any AC coupling or filters yet, I'm not even sure that I'll need them given the source, but I think I want to build a physical mockup first and adjust as needed.Thanks for your help!

author: Hideki
author_rank: Frequent Contributor
timestamp: September 23, 2015, 01:22:54 am
content: That is a strange device you have inventedUnfortunately it doesn't work like it should in any of the modes. As drawn it looks a bit like the first part of an instrumentation amplifier, but there are no resistors on the non-inverting inputs to ground, so you have almost infinite input impedance. For a mic preamp, those resistors would be rather small in value (closer to 1k than gigaohms), or the mic will be completely unloaded. Gain is usually set by a variable resistor linking the two halves (R4 and R5 in your case). This is followed by a normal single-op-amp differential amp.With S1 and S2 in the other position I don't see how it will "recombine them as a mono output". Note that the microphone signal IS already mono. It's just balanced (or differential) - not left and right.You end up with one op amp doing nothing and the other being a non-inverting amplifier - again with a sky-high input impedance.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: September 23, 2015, 01:41:23 am
content: KISS. How about just putting a phase reversal switch on the input?
op-amp theory and learning - Page 1
Forum section: electronics / beginners

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 23, 2012, 08:31:55 pm
content: heyI know pretty much what op-amp are etc , but I'm looking for some good reading+photos about all the diffrent parameters and the aplications who exsist ,thank you in advance !

author: Simon
author_rank: Unknown
timestamp: June 23, 2012, 09:04:06 pm
content: The art of electronics has a whole section on op-amps, or there is a pdf book lurking on the net but it's 500 pages of solid op-amp stuff, never read it myself

author: MikeK
author_rank: Super Contributor
timestamp: June 23, 2012, 09:13:41 pm
content: Understanding Op-Amp Parameters:www.ti.com/lit/ml/sloa083/sloa083.pdf

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 23, 2012, 09:18:22 pm
content: thank you both !I've red a bit the link you've posted , but have no time now for further reading , I'll do that either tommorow or in monday , it looks promesing to be the title I was looking for , thank you

author: Zad
author_rank: Super Contributor
timestamp: June 24, 2012, 02:57:23 am
content: Analog Devices has one of the standard textbooks on Op-Amps, free for pdf download:http://www.analog.com/library/analogDialogue/archives/39-05/op_amp_applications_handbook.html

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 25, 2012, 08:29:45 am
content: heywell , thank you . I've red both the links , I'm now floating with info , does someone know some practice article or any thing simmilar ? (I've serched and practiced via some sites etc , but I mean more like " engineering chaleng" or so , assuming that title existe 0_0 ? )anyhow , thank you a-lot !

author: johnboxall
author_rank: Unknown
timestamp: June 25, 2012, 09:25:00 am
content: http://www.talkingelectronics.com/projects/OP-AMP/OP-AMP-1.html

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 25, 2012, 10:22:25 am
content: heythank you , as I've said , I've serched in google for practicing already , and that one as well , but thanks anyhow !
op-amp, TL081 - 400ST Ultrasonics, Headbanging... - Page 1
Forum section: electronics / beginners

author: rdbanks
author_rank: Contributor
timestamp: May 07, 2018, 11:40:15 am
content: Hi guys, I'll keep this short, its a bit of a noob question however i'm trying to get my head around this to explain it the most accurately...I have a simple TL081 op-amp acting as an Astable multivibrator +/- 12V supplies - this 40kHz output is then fed into another TL081 set up as a non-inverting unity buffer which feeds an ultrasonic transducer (looking for 40kHz (receiver tuned) transmitting).Now, my question....I understand, without the buffer, the transducer would 'load' the first op-amp however I cant explain this the way I understand it... Simply put, as i recall, the transducer acts as a capacitance in the op-amp circuit, if that right? I tried measuring DC current through the transducer and it came up at around 9.1uA - am I measuring this correctly - AC current is around 3mA. AC or DC? I was happy with my understanding until now, perhaps its exam prep and i'm thinking too much...I think my issue is i'm confusing my basic understanding due to the circuit involving op-amps, I've confused a lot with BJTs lately and was wondering if someone could elaberate on my question which was:Is it more important to use a buffer to 'remove the load' or 'remove the capacitance'.This isn't a coursework/exam question, just more of a understanding exercise.I've found this post hard to explain, I hope you smarter bunch can shed some light... Thanks. Ryan!// the clean sq wave is Vout of the first TL081, with a buffer after connecting to the transducer.// the deformed wave, is Vout of the first TL081 with transducer connected directly - this is the same wave form as seen at Vout2 (second TL081 (buffer)) with the transducer connected to that.//Frequency reading is different, before and after tuning, it doesnt really matter for the question).

author: mikerj
author_rank: Super Contributor
timestamp: May 07, 2018, 02:37:14 pm
content: Quote from: rdbanks on May 07, 2018, 11:40:15 amWhen you are dealing with AC (with or without a DC offset), capacitance IS a load.

author: rdbanks
author_rank: Contributor
timestamp: May 07, 2018, 03:39:07 pm
content: I see! I've just taken 5mins away from analog and its all clicking!Thanks Mikerj!
Op amp triangle generator - how to get a constant amplitude - Page 1
Forum section: electronics / beginners

author: tbj
author_rank: Contributor
timestamp: December 24, 2012, 06:30:47 pm
content: Hi,I'm building a function generator, and I have two op amps configured like this:R1 is a variable resistor, and I select different values for C1 to get the frequency ranges. I am using a TL082 op-amp. As I increase the frequency up towards around 300kHz, I find that the amplitude of the output triangle wave increases - at very low frequencies the amplitude is around 0.5v P-P; near 300kHz it's around 10 volts on a 15 volt supply.I am going to use another op-amp to amplify the triangle wave, so 0.5v P-P would be fine, but how can I get the circuit to maintain a constant amplitude over the entire range of frequencies? Is it possible?Cheers.

author: Zero999
author_rank: Super Contributor
timestamp: December 26, 2012, 02:33:57 pm
content: That's odd, I'd expect the output to be lower at higher frequencies - the TL082 will struggle at 300kHz.

author: AndyC_772
author_rank: Super Contributor
timestamp: December 26, 2012, 03:25:36 pm
content: Not really; a triangle wave oscillator works by integrating a square wave, and if there's a delay between the triangular output reaching the programmed limit of its excursion and the square wave changing stage, the output will overshoot. The problem is likely to be down to the bandwidth of OA1, and the solution could be something as simple as a small capacitor across R3.

author: w2aew
author_rank: Super Contributor
timestamp: December 26, 2012, 09:00:04 pm
content: The other thing that can cause an unexpected rise at higher frequencies would be an improperly compensated 10x probe on the scope.

author: marinedalek
author_rank: Contributor
timestamp: December 26, 2012, 09:22:19 pm
content: The output of the left hand op-amp will typically have a peak-to-peak swing of 13.5V on a 15V supply. If you look at the slew rate, that equates to roughly 1 µs taken for each swing. If the wave being produced measures as 300 kHz, bearing in mind a single cycle will comprise two swings, the switching time would account for 60% of the cycle. The output probably looks more like a triangle wave with sine-wave-like tips, due to the integration of the falling ramp as the left op-amp switches. Only the remaining 40% of the wave is actually linear ramp.Although wasteful in terms of layout size, the ideal solution is to use a fast-switching comparator for the left-hand op-amp such as an LM319, though you'll always come up against a frequency limit at some point.

author: AndyC_772
author_rank: Super Contributor
timestamp: December 27, 2012, 09:46:09 am
content: Quote from: w2aew on December 26, 2012, 09:00:04 pmThat wouldn't explain a factor of 20:1 between the low frequency and high frequency responses of the circuit.

author: Zero999
author_rank: Super Contributor
timestamp: December 27, 2012, 01:57:56 pm
content: Quote from: marinedalek on December 26, 2012, 09:22:19 pmThe circuit might work with both comparators. The LM393 works in LTSpice. I haven't tried it in real life though.
Op amp trouble - Page 1
Forum section: electronics / beginners

author: RippoZero
author_rank: Newbie
timestamp: August 01, 2023, 04:41:49 am
content: Hi there! I've been laying out a circuit using the AMC1300 and I stumbled over a very helpful design document from TA where they go over some of the non-ideal behavior of the amp. The guys that wrote it first go over how to select external resistors for your voltage divider giving us this:They then illustrate the error such a setup would entail and go over how to select a new value for R3 before introducing R3' on the negative input to compensate for the input current. This gives us this:I understand the first part but get confused when they introduce the new value for R3. My initial understanding was that they took the voltage divider formula $$Gain = \frac{R3}{Rtop+R3}$$ and substituted the old R3 with the parallel resistor formula $$Gain = \frac{\frac{R3*Rind}{R3+Rind}}{Rtop+\frac{R3*Rind}{R3+Rind}}$$ solving for the new R3 giving us $$R3=-\frac{Gain*Rind*Rtop}{Gain(Rtop+Rind)-Rind}$$The idea being that you now have the same gain on the voltage divider, however when I input the same values as they used I get a different R3 than they did. Clearly our formulas are derived differently.Their formula is in the picture bellow. The one i derived resulted in a value of 5134 ohm.The guys in the document know what they are doing and their simulated values were correct so there is something I don't get here. Won't their value for R3 result in wrong gain for the voltage divider? How did they obtain their formula for R3?A little insight would be much appreciatedAMC1300 datasheet:https://www.ti.com/lit/ds/symlink/amc1300.pdf?ts=1690846311394&ref_url=https%253A%252F%252Fwww.google.com%252Fdesign doc:https://www.ti.com/lit/an/sbaa350a/sbaa350a.pdf?ts=1690486466551&ref_url=https%253A%252F%252Fe2e.ti.com%252F

author: MasterT
author_rank: Frequent Contributor
timestamp: August 01, 2023, 01:09:27 pm
content: There are two input impedances:Input Resistance 19kΩ (typ, single-ended), 22kΩ (typ, differential)I used this calculatorhttp://www.sengpielaudio.com/calculator-paralresist.htmand get 5.3425 k for SE input and 5.1452 for Diff.Trash these paper, overall idea to balance input impedances seen by both inputs of the diff modulator ( increasing CMRR ) looks correct, but I'd be very cautious for non-linerity introduced by doubling input impedances.Even 4.17k is not good, but pushing it over 13k is absurd, IMHO.

author: RippoZero
author_rank: Newbie
timestamp: August 02, 2023, 06:50:41 am
content: After some thought I realize this amp was probably a bad choice to begin with. Went with the ISO224 instead. Still wondering where they got that formula from thought
Op-Amp unbalanced rail voltage? - Page 1
Forum section: electronics / beginners

author: ftransform
author_rank: Frequent Contributor
timestamp: March 21, 2013, 07:06:04 pm
content: For a dual supply op-amp are they any negative effects from having un-equal rail voltages other then having a smaller output range?I.E. If one rail is 15.5 and the other is 14.7 is there any kind of degradation of specifications, such as PSRR, noise, bias currents, whatever.

author: amspire
author_rank: Super Contributor
timestamp: March 21, 2013, 07:10:38 pm
content: None at all.

author: Neilm
author_rank: Super Contributor
timestamp: March 21, 2013, 07:13:15 pm
content: I've measured nA with on op-amp supplied from +15V and -8V.No problem what so ever.Neil

author: Unknown
author_rank: Unknown
timestamp: March 21, 2013, 08:02:53 pm
content: Just need to keep in mind your supply rail to rail max, verses signal out, peak to peak before clipping.

author: SeanB
author_rank: Super Contributor
timestamp: March 21, 2013, 08:13:37 pm
content: I have seen many use a rail of -0.6V ( a diode drop above negative rail) and 11.6V as supply, just because this allowed an output to be very close to 0V, while allowing positive voltages in with no problem. Fails with an inverting amplifier though, but fine for many applications.

author: ftransform
author_rank: Frequent Contributor
timestamp: March 21, 2013, 09:10:23 pm
content: I swear though once I was taking measurements once and the AC measurement from my multimeter indicated that there was less noise when I increased the rail voltage from like 5 to 15.I don't remember the setup though.

author: c4757p
author_rank: Super Contributor
timestamp: March 21, 2013, 09:27:59 pm
content: Quote from: ftransform on March 21, 2013, 09:10:23 pmOp amps can definitely have different characteristics with different rail to rail voltages across them, it's the relative location of ground between them that doesn't make a difference. -1V/11V should be the same as -6V/6V, but (obviously) not -1V/1V.

author: ftransform
author_rank: Frequent Contributor
timestamp: March 22, 2013, 12:50:50 am
content: Quote from: c4757p on March 21, 2013, 09:27:59 pmah ha i am not crazy

author: c4757p
author_rank: Super Contributor
timestamp: March 22, 2013, 01:00:05 am
content: Also, I've seen some fantastically crappy power supplies that were noisier at low voltages (presumably due to the long wires going to the voltage pot picking up noise and not being adequately filtered), so the power supply may be injecting noise as well.

author: ftransform
author_rank: Frequent Contributor
timestamp: March 22, 2013, 01:53:03 am
content: This is possible my PSU is old. I really should take it apart and test capacitors at least.

author: rdl
author_rank: Super Contributor
timestamp: March 22, 2013, 11:29:44 am
content: w2aew has a good video on op power supplies.
Op Amp Unity Gain Stability - Page 1
Forum section: electronics / beginners

author: Etesla
author_rank: Regular Contributor
timestamp: May 31, 2019, 04:53:16 pm
content: I want to use an opamp as a non inverting buffer. I know that a lot of op amps are not 'unity gain stable'. Is using an op amp as a non inverting buffer (gain of +1) considered using it at unity gain, or does unity gain in the context of 'unity gain stability' only refer to an inverting buffer where R1 and R2 are the same value? Thanks.

author: Benta
author_rank: Super Contributor
timestamp: May 31, 2019, 05:25:40 pm
content: It refers to both +1 and -1 gain.

author: Wimberleytech
author_rank: Super Contributor
timestamp: May 31, 2019, 05:40:28 pm
content: ^^^^ ditto what he saidSee my comment below modifying this answer.

author: magic
author_rank: Super Contributor
timestamp: May 31, 2019, 09:49:15 pm
content: I thought unity gain means exactly +1 and nothing else?Gain of -1 doesn't actually require a unity gain stable amp, but one stable at 2 or more. It's noise gain that matters.

author: Zero999
author_rank: Super Contributor
timestamp: May 31, 2019, 10:15:36 pm
content: Quote from: magic on May 31, 2019, 09:49:15 pmYes, that's true. It's the noise gain which matters. An op-amp which is not unity gain stable can easily be used as a buffer, by setting the noise gain to a high enough value. It does increase noise, but this can be mitigate somewhat by only having a high noise gain, at high frequencies, which cause oscillation. Noise is also less of an issue for a buffer, as the signal level is generally very high.An application of this is connecting two audio amplifier ICs together to make a bridged output. A gain of -1 is required to make one side inverting, but many audio amplifier ICs need a much higher gain to be stable. The solution is to set the noise gain high enough to be stable, even through the signal gain is unity.See the thread linked below for more information.https://www.eevblog.com/forum/beginners/op-amp-spec-noise-gain-configuration/msg2401983/#msg2401983

author: Wimberleytech
author_rank: Super Contributor
timestamp: May 31, 2019, 10:30:42 pm
content: Quote from: magic on May 31, 2019, 09:49:15 pmYes, you are correct. Feedback factor (beta, or b) for an inverting amp with a gain of -1 is 1/2. Thus when 1+Ab=0, A is 2 for b=1/2.
op-amp unity gain stability  - Page 1
Forum section: electronics / beginners

author: Kdog44
author_rank: Contributor
timestamp: October 21, 2014, 01:28:19 am
content: Biased on the bode plot of an op-amp's open loop gain, how could one tell if the op amp is unity gain stable?

author: planet12
author_rank: Regular Contributor
timestamp: October 21, 2014, 05:54:27 am
content: To be able to find this, the plot will need to have phase as well as amplitude.Many others can explain this better than me - the magic google phrases are "phase margin" and "gain margin" - you're looking to find the phase margin at the point the gain drops through 0dB, and that said phase margin is greater than 45 degrees ("Nyquist stability criterion" if you want to get all technical about it).This all assumes a standard dominant-pole compensated op-amp - which most are. If you've got strange dips then rises in gain things get more complicated.

author: LvW
author_rank: Frequent Contributor
timestamp: October 21, 2014, 07:45:20 am
content: Quote from: planet12 on October 21, 2014, 05:54:27 amTheoretically, the circuit is "stable" even for a phase margin of some degrees only. However, if this margin is too small (for example, less than 45 deg) the step response will exhibit heavy overshoot or ringing. If the margin is larger than app. 65 deg. there will remain a very small overshoot only.

author: planet12
author_rank: Regular Contributor
timestamp: October 21, 2014, 07:47:05 pm
content: Quote from: LvW on October 21, 2014, 07:45:20 amQuite right - I put the 45 degrees figure in as that is the common rule of thumb for the minimal "usefully stable" margin.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 21, 2014, 11:46:37 pm
content: Quote from: planet12 on October 21, 2014, 05:54:27 amNot necessarily. If the response isn't terribly pathological, you can tell phase shift from attenuation rate: every 20dB/decade is 90 degrees.http://en.wikipedia.org/wiki/Minimum_phase#Relationship_of_magnitude_response_to_phase_responseFortunately, most simple components, amps and circuits are like this, so it's handy to know. A component-level example: you can tell the inductivity, or Q, or loss, or whatever of something like a ferrite bead based on the slope of the impedance: rising at 20dB/decade it's inductive, flattening out it's resistive, descending and it's capacitive. (It's interesting because some materials -- nanocrystalline common mode chokes are one example -- exhibit a slope over a useful range which is not a multiple of 20dB/dec!)Tim

author: LvW
author_rank: Frequent Contributor
timestamp: October 22, 2014, 07:24:48 am
content: Quote from: T3sl4co1l on October 21, 2014, 11:46:37 pmPerhaps it is helpful to add that the above rule (90 deg for each 20dB/dec drop) gives a set ofasymptoteswhich can (and must be !) be used to find the approximate real phase response. As an example, many opamps have a second pole in the vicinity of the transition frequency (where the open-loop gain crosses the 0 dB line). Hence, theasymptoticattenuation rate now will be 40dB/dec. Hence, the phase margin will be roughly between 90 deg and 0 deg: 45 deg approximately.
Op amp voltage follower cutting sawtooth waveform off at positive peak  - Page 1
Forum section: electronics / beginners

author: Ryan OMalley
author_rank: Newbie
timestamp: March 28, 2020, 08:44:56 pm
content: Hi everyone, I’m having an issue with the voltage follower between the capacitor and the comparator in my vco circuit. When I connect the probe of my oscilloscope to the capacitor, the waveform looks pretty good, but when I connect my scope probe to the output of the tlo81 i’m Using as a non-inverting voltage follower, it seems to be chopped off before the positive peak. The sawtooth wave is 6.8 volts peak to peak, and it almost seems like the op amp can’t swing close enough to the positive rail, but it doesn’t have a problem with the negative part of the waveform. I will attach two pictures below: one is of the waveform read directly from the capacitor, and the other one is the waveform off of the tlo81. Any suggestions on how to improve the circuit will be greatly appreciated.

author: rstofer
author_rank: Super Contributor
timestamp: March 28, 2020, 09:38:28 pm
content: The op amp number doesn't compute (for me...) but look for the output voltage swing in the datasheet. It will tell you how close you can get to the rails.In the case of the LM741, the minimum output swing could be as low as +-10V with a +- 15V supply and a 2k load. Page 5 Section 6.5http://www.ti.com/lit/ds/symlink/lm741.pdfA schematic might helpIt sure looks like the op amp is clipping.

author: magic
author_rank: Super Contributor
timestamp: March 28, 2020, 09:44:57 pm
content: If it works down to the negative supply it's not a TL081Most cheap junk from auction sites are actually LM358, apparently the cheapest opamp available in China these days.
OP AMP: what is output SWING? - Page 1
Forum section: electronics / beginners

author: jagan
author_rank: Newbie
timestamp: May 30, 2014, 06:08:16 am
content: Hi all,i would like to know below op amp basic parameters.1) what is output SWING?2) what is small signal bandwidth? and large signal bandwidth?3) Gain?please reply me,thanks,Jagan.

author: Bored@Work
author_rank: Super Contributor
timestamp: May 30, 2014, 06:11:38 am
content: http://www.ti.com/lit/an/slod006b/slod006b.pdf
OP AMP - Page 1
Forum section: electronics / beginners

author: jagan
author_rank: Newbie
timestamp: May 30, 2014, 05:40:38 am
content: What is OP AMP small signal bandwidth? and large signal bandwidth?

author: Bored@Work
author_rank: Super Contributor
timestamp: May 30, 2014, 06:12:04 am
content: http://www.ti.com/lit/an/slod006b/slod006b.pdf

author: JOERGG
author_rank: Contributor
timestamp: May 30, 2014, 06:46:20 am
content: http://www-inst.eecs.berkeley.edu/~ee105/sp08/discussions/discussion3.pdf
Op amps and their varieties - Page 1
Forum section: electronics / beginners

author: Belrmar
author_rank: Regular Contributor
timestamp: April 27, 2017, 09:19:23 pm
content: Hello forumI am starting to learn analog elechtronics lately and i am starting to struggle with the opamps and their varieties, such as jellybeam rail to rail, preamp and all those names that the internet seems not really willing to teach meany advice will bea lot of helpalso i am a bit confused with the ne 5532 datasheet showingDoes this mean that it has included the resistances included so i can only use it as an amplyfier?Thanks for your help and i apologice for my bad english

author: rstofer
author_rank: Super Contributor
timestamp: April 27, 2017, 09:26:44 pm
content: Quote from: Belrmar on April 27, 2017, 09:19:23 pmjellybean => garden variety op amp with no particularly significant characteristics. There are better parts, there are worse...rail to rail => older op amps could not have output voltages that came anywhere near the positive or negative supplies. Maybe they could get within a couple of volts but that was about it. No big deal, we use +- 15V supplies and plan for +-10V signal and output swings.So, with rail-to-rail, the inputs and outputs can swing all the way to the supply rails (or very close). What good would it be to have a 5V op amp that could only swing about a volt because it couldn't get within 2V of the rails?QuoteNo, the resistors are not internal. If you look at Figure 9 on Page 12 you will see that these are external components:http://www.ti.com/lit/ds/symlink/ne5532.pdf

author: james_s
author_rank: Super Contributor
timestamp: April 28, 2017, 06:12:45 pm
content: To the beginner, op-amps are pretty much interchangeable. Don't worry about these characteristics too much for the time being, something basic like the TL082, LM324 or even the humble 741 will work just fine for experimentation. More specialized op amps are optimized for various tasks but on a very basic level they all work the same way.
Op amps - assignment  - Page 1
Forum section: electronics / beginners

author: darko31
author_rank: Regular Contributor
timestamp: November 10, 2014, 07:26:54 pm
content: Hi guys,we've been given an extra points assignment in my electronics class, and I've been having some trouble with it. The assignment is in the attachment. Basically, the OP1 and OP2 are configured as non-inverting, but the OP0 and OP3 are giving me headaches. I'm stuck at b) point, to find out V0 in function to V1, V2 and V3.The OP3 is configured as buffer and it's just transferring input from pot, but the OP0 looks like it's configured as differential amp although R3 should be connected to ground. My way of seeing it is like the OP3 and pot are shifting the ground for the R3 but the problem is that I'm not sure how to write it down in equations.So far, I've got this V1=Va+R1(Va-Vb)/xP and V2=Vb-R1(Va-Vb)xPand for the OP0, V0=R3/R2(V2-V1) + something with V3I'll be reaching my teaching assistant, but I'd like to hear what eevbloggers have to say.Thanks in advance.

author: XFDDesign
author_rank: Frequent Contributor
timestamp: November 10, 2014, 07:59:54 pm
content: It's an instrumentation amplifier configuration. The amplifiers are not labeled, and I can't read the assignment. Can you redraw with labels?

author: darko31
author_rank: Regular Contributor
timestamp: November 10, 2014, 08:15:20 pm
content: Yeah, sorry about that

author: jimmc
author_rank: Frequent Contributor
timestamp: November 10, 2014, 09:08:08 pm
content: Might be worth taking a look at this ti.com articlewww.ti.com/lit/an/slyt226/slyt226.pdfJim

author: XFDDesign
author_rank: Frequent Contributor
timestamp: November 10, 2014, 09:12:24 pm
content: You've then got the basics, but you're relying too much on patterns and not analysis.If you know V2 and V3, you can solve the voltage at the non-inverting node by superposition.

author: free_electron
author_rank: Super Contributor
timestamp: November 10, 2014, 09:48:37 pm
content: solve it for R3 tied to 0 v . this is a classic diff amp.then replace 0v with the voltage coming from the other opamp.tis is basically a diff amp with offset control for its output. last stage acts as summing amplifier

author: darko31
author_rank: Regular Contributor
timestamp: November 10, 2014, 10:06:36 pm
content: @jimmcWill do.Quote from: XFDDesign on November 10, 2014, 09:12:24 pmYeah, I'm still grasping the methods of solving opamp circuits. Will try that out.Quote from: free_electron on November 10, 2014, 09:48:37 pmYup, got similar idea, thanks for confirmation.
Op-amp's input offset voltage simulation - Page 1
Forum section: electronics / beginners

author: Axk
author_rank: Regular Contributor
timestamp: May 23, 2020, 02:15:39 pm
content: Simulating a constant-current load circuit with an op-amp (LT318A), a built-in model of the op-amp.The datasheet of the op-amp specifies the offset input voltage at 1 mV.Masuring the difference between IN+ and IN- in the simulation gives me only 9 uV.Does this mean the model doesn't account for input offset voltage?

author: Zero999
author_rank: Super Contributor
timestamp: May 23, 2020, 02:47:08 pm
content: No, it doesn't model offset voltage. Add another voltage source in series with one of the inputs to do that.

author: Axk
author_rank: Regular Contributor
timestamp: May 23, 2020, 04:01:36 pm
content: Adding a constant 1mv offset voltage source degrades my current regulation 20 fold.I was expecting just a constant error, but something different's happening.I wonder if this is something that would happen in real life or there's yet another unaccounted for thing in the model.

author: Axk
author_rank: Regular Contributor
timestamp: May 23, 2020, 06:44:45 pm
content: Turns out the MOSFET is just too close to saturation and this extra 1mV is enough to push it far enough to prevent it from regulating with the required precision.

author: Zero999
author_rank: Super Contributor
timestamp: May 23, 2020, 10:42:03 pm
content: For future reference, there's also the offset current which is also not modelled.
OP Schematic Voltage to Current Converting ExpLog - Page 1
Forum section: electronics / beginners

author: richi
author_rank: Newbie
timestamp: August 23, 2018, 07:41:51 pm
content: Hi,i want to make Voltage to Current converting, but not linear, i need it ExpLog.0-5V is the Control Voltage for Input to the OPV.Output is like an LED with breakdown voltage 2-4V and its have a treshold current, example 50-200mANow i want the 0-5V translate it to "treshold current" -> 1AIf 0V then treshold current goes to 0mA and if 0,1V then start treshold Current and makes it exponetial function to the max values.Any idea ?

author: Signal32
author_rank: Frequent Contributor
timestamp: August 23, 2018, 11:28:22 pm
content: I assume you didn't nt want to go the door gital route ? ADC + Micro + DAC ? Then you can do whatever you want with conversion.

author: richi
author_rank: Newbie
timestamp: August 24, 2018, 12:20:59 pm
content: Hi Signal32,I would like to implement the purely analog, otherwise there would be time delays, and i need it up to 100kHz.analog digital would certainly be a fine solution, but the effort would be too big, because I need the whole at least 3 times

author: MasterT
author_rank: Frequent Contributor
timestamp: August 24, 2018, 12:43:02 pm
content: Can't see a point to have 100kHz (10 usec) response time for LED. Visual perception by human being is more than 40 milliseconds, AFAIK, though 25 Hz should be sufficient.

author: richi
author_rank: Newbie
timestamp: August 24, 2018, 12:48:48 pm
content: it's not about the LED and the viewing with the eye. I'm only interested in the analog circuit with operational amplifiers.

author: eev_carl
author_rank: Regular Contributor
timestamp: August 24, 2018, 02:00:17 pm
content: There's a linear to exponential voltage converter in the middle of this DIY Synth page. I think you can leave off the second op amp if you don't care about converting the result back to a voltage.https://www.allaboutcircuits.com/projects/diy-synth-series-vco/

author: exe
author_rank: Unknown
timestamp: August 24, 2018, 03:07:17 pm
content: AFAIK all log/exp circuits based on PN-junction suffer from serious temperature drift. Never seen this addressed.

author: David Hess
author_rank: Super Contributor
timestamp: August 24, 2018, 07:32:50 pm
content: Quote from: exe on August 24, 2018, 03:07:17 pmThe PN junctions are either used in matched pairs with a 3300ppm/C resistor or a single PN junction is ovenized. Either is a very routine circuit when translinear accuracy over temperature is required.
OPA2132P Output to led - Page 1
Forum section: electronics / beginners

author: lawfreak
author_rank: Newbie
timestamp: April 04, 2016, 07:52:54 pm
content: Previously I had a potentiometer wired as a voltage divider feeding the non-inverting input of one of the opamps in an OPA2132P. The opamp output was fed to the base of an NPN power transistor. The output of the transistor powered some leds and was fedback to the inverting input of the opamp. This worked well as a dimmer for a bunch of paralleled leds.Now, I have removed the transistor and am powering a single LED off the output of the opamp. The opamp output is connected to the noninverting input.Before, I could drive the voltage up to near the 12V supply, but now the voltage peaks at roughly 2.5V with the LED in circuit. When the LED is removed, the voltages behave as before.Why is my opamp not matching its inverting and non-inverting inputs as expected? 12V -> non-inverting and 2.5V -> inverting/output

author: michaeliv
author_rank: Frequent Contributor
timestamp: April 04, 2016, 08:34:32 pm
content: Probably because the short-circuit current of the op-amp is ~40mA according to the datasheet.So, perhaps you're hitting that limit at around 2.5V output and the voltage can't go any higher.Have you measured the current at 2.5v through the LED ?

author: danadak
author_rank: Super Contributor
timestamp: April 05, 2016, 10:12:49 am
content: You are trying to voltage drive a diode, which means, because of its logarithmic curve,very large current flows occur for very small voltage changes. So as previous postermentioned the OpAmp is probably going into current limit.One fix is to put a series R from out of OpAmp to LED. Start with 100 ohms and adjustas needed. Note overdriving LED shortens its lifetime, severe overdriving will burn itout, destroy its light producing junction.Or change circuit to current drive. Google this "op amp constant current" and you willsee possible circuit solutions.Regards, Dana.
Opal Kelly 7310 Pin Mapping - Page 1
Forum section: electronics / beginners

author: loftusmi
author_rank: Newbie
timestamp: February 20, 2024, 01:16:33 pm
content: Hello,I'm designing a PCB to interface with an OpalKelly XEM7310 that I plan to configure with some open source firmware. I'm trying to connect the PCB traces to the correct pads for the PCB/XEM7310 pin connector so that the firmware will not require modification for different pins. However, I'm not finding an I/O pin map for the XEM7310 online like one might find for a microcontroller. Opal Kelly does explain which MC1/MC2 pin that the FPGA maps to, but I don't see where it says which MC1/MC2 pin is which on the XEM7310 (nor do I really understand what MC1/MC2 means). Am I misunderstanding something about the way FPGA pins work or have I not found the proper documentation yet? If it's the latter case, does anyone know where I can find the pin map that I'm looking for?OS Firmware Documentation:https://intantech.com/files/Intan_RHD_XEM7310_interface.pdfPCB/XEM7310 pin connector:https://www.samtec.com/products/bteOpal Kelly XEM7310 Pin Reference:https://pins.opalkelly.com/pin_list/XEM7310

author: loftusmi
author_rank: Newbie
timestamp: February 20, 2024, 07:14:44 pm
content: Figured it out! I just needed to click on one of the table rows on the Pin Reference site. Then the map that I'm looking for appears above.