hybridfree/eevblog-posts huggingface dataset:
Op-amp supply voltage vs noise - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: November 14, 2020, 06:57:40 pm
content: Hi,in a dual-supply op-amp design, does the supply voltage in any way affect the noise?Does higher voltage increase noise, decrease it or does not affect it at all?Thank you

author: Kleinstein
author_rank: Super Contributor
timestamp: November 14, 2020, 07:21:39 pm
content: There can be a small effect of the supply on the noise. Which way and how much depends on the OP type. It can be either way and normally the effect is rather small, especially with newer types. Some older type may have a not so stable current biasing and this way can have a decreasing noise with increasing supply current when the supply goes up.Higher voltage can increase the 1/f noise in JFETs, so a higher voltage can also be bad.

author: David Hess
author_rank: Super Contributor
timestamp: November 14, 2020, 08:05:36 pm
content: Quote from: ricko_uk on November 14, 2020, 06:57:40 pmWith some exceptions, the effect of supply voltage on noise is insignificant unless it changes the operating point of the circuit.Dual supply circuits which use tracking so that noise is mirrored between the supplies do not have to rely on common mode rejection to reject noise as much, and tracking supplies are sometimes used for exactly this reason in the lowest noise applications. So there is some benefit especially when common mode rejection is limited.
Op Amp Triggers When It's Not Suppose To - Page 1
Forum section: electronics / projects

author: epicode
author_rank: Newbie
timestamp: November 11, 2019, 12:31:49 pm
content: Hello, I've been working on a boost converter for a long time now and my control system needs to provide two high frequency inverted signals (when one is high the other one has to be low) and I've been using two comparators for that, both of them get a voltage reference (some constant DC voltage) and a triangle wave just that the inputs are swiped so that the required signal can be generated but for some reason the two signals are phase-shifted like the attachment below, I've checked the triangle wave and it is in perfect sync in both inputs.. the op amp is OPA2691I and as you can see in the picture the op amp seems to trigger in a weird way.. any ideas ?Modify message

author: Simon
author_rank: Unknown
timestamp: November 11, 2019, 12:51:24 pm
content: I am sorry but you can't have two identical topics:https://www.eevblog.com/forum/beginners/dual-comparator-output-is-phase-shifted/msg2779672/#msg2779672this will just annoy people. Please only post your topic once.
OP-AMP Vgnd option for LM339 - Page 1
Forum section: electronics / projects

author: dave_j_fan
author_rank: Regular Contributor
timestamp: March 14, 2015, 03:50:03 pm
content: Hi I am trying to swap a LM339 into the vu meter circuittaking reference of other circuits in net created vgnd with 1x 47K as shown .I want to use a single 12Vis it right way ?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 14, 2015, 07:03:02 pm
content: LM339 is a comparator, it will not behave correctly in this circuit.A voltage divider is a common way to generate a 'virtual ground', yes. You have to avoid drawing DC current through the node, however, otherwise the center point shifts.Tim

author: dave_j_fan
author_rank: Regular Contributor
timestamp: March 14, 2015, 08:19:55 pm
content: The LM339 can pull the output as low as 0.2V or as high as Vcc, by virtue of its open-collector output.but for vu meter will that be not enough , U1A is main for vu ?(got infor herehttp://electronics.stackexchange.com/questions/72967/difference-between-differential-op-amp-and-comparator)i remember the rail splitter i used for CMOY with BJT it will be a better choice
Op-amp voltage supply question - Page 1
Forum section: electronics / projects

author: JimmyM
author_rank: Regular Contributor
timestamp: January 28, 2012, 09:08:44 pm
content: Does an Op-amp (if I'm going to power it with + & - supply) HAVE to be balanced? Does the V+ need to be almost exactly the same as the V- supply?Can I use a +18V V+ and a -5V V-? I'll never need to the output to go below about -1V. But I'll need the output to go to around 15.5-16V. A pair of fixed regulators (LM7818 and LM7905) can supply the + and - rails.The number of Op Amps to choose from is greater if I only have to use a V+ to V- diff of 22V versus 36V.

author: Rerouter
author_rank: Super Contributor
timestamp: January 28, 2012, 09:12:18 pm
content: aslong as its within your minimum +- supply range, you will be fine, and if you dont have any reference to ground on the op amp, it doesnt have to be negative, unless you need a non rail to rail one to work to 0V

author: ejeffrey
author_rank: Super Contributor
timestamp: January 28, 2012, 09:15:30 pm
content: Quote from: JimmyM on January 28, 2012, 09:08:44 pmNo. The supplies just have to be wide enough to support whatever input/output voltages you need, plus the appropriate margin for non rail-to-rail opamps.

author: JimmyM
author_rank: Regular Contributor
timestamp: January 28, 2012, 10:10:20 pm
content: Ehhhhxcelent.Thanks, guys.
op07  - Page 1
Forum section: electronics / projects

author: electros6
author_rank: Regular Contributor
timestamp: November 17, 2013, 04:44:15 pm
content: I tried to connect op07 in differential configuration for high side current sensing . Even when nothing connected to the input there is around 1.2 V in the output . I tried 3 op07 but ended in same. Please tell me is this their original characteristics or I am wrong

author: dannyf
author_rank: Super Contributor
timestamp: November 17, 2013, 04:54:42 pm
content: QuoteWhat does the datasheet say about that?

author: SeanB
author_rank: Super Contributor
timestamp: November 17, 2013, 04:56:25 pm
content: Resistor tolerances, or you are out of the input common mode voltage range. What is the offset if you connect the inputs to your analogue ground, and what supply rails are you using for the OP07 and what is the value of the resistors you used for the divider.

author: Relaxed
author_rank: Contributor
timestamp: November 17, 2013, 05:09:03 pm
content: What a poor topic title.

author: BravoV
author_rank: Super Contributor
timestamp: November 17, 2013, 05:14:15 pm
content: You connected the power supply wrongly, try reverse the connections.

author: tszaboo
author_rank: Super Contributor
timestamp: November 17, 2013, 05:14:43 pm
content: The OP07 swings only about 2 volt from the power supply. Why dont you try to measure the current with something which is made for that?http://nandblog.com/types-current-sense-amplifiers/

author: bdivi
author_rank: Regular Contributor
timestamp: November 18, 2013, 04:03:08 pm
content: If OP07 is properly powered by supply that is symmetric to the high side then the output will naturally swing around the high side. You have to convert that high side signal to low side.Without schematic we will not be able to help more.
OPA1612 as input buffer - Page 1
Forum section: electronics / projects

author: firstcolle
author_rank: Regular Contributor
timestamp: December 20, 2017, 02:45:49 pm
content: Hi,can I use OPA1612 as input buffer for audio application? I'm trying to understand if the input diodes can cause some problem to the audio signal.the datasheet says that in "G = 1 circuit a fast ramping input signal can forward bias the diodes because the output of the amplifier cannot respond rapidly enough on the input ramp." but I think that is not the case of an audio signal right?thanks

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 20, 2017, 03:03:56 pm
content: That wouldn't bode well for TI if their "SoundPlus" audio line couldn't be used for audio purposes...You're right, take a look at fig.17 of the datasheet, which is supposed to illustrate the phenomenon. Your input signal would probably have to have very high bandwidth (in the MHz range). They suggest workarounds if this is the case, but your best bet would probably to band-limit your input signal (if it's not already guaranteed to) to avoid all problems.

author: firstcolle
author_rank: Regular Contributor
timestamp: December 20, 2017, 03:23:32 pm
content: yes.. I have a bandpass filter 2Hz 300Khz (-3db) before the buffer.. probably I can decrease the 300Khz without affecting the audio frequencies

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 20, 2017, 05:20:29 pm
content: Is your filter passive? If so, you probably already have a resistor in series that would limit the input current anyway, like TI suggests in the datasheet. And yes you could lower the high frequency, 300 kHz is largely overkill for audio

author: DaJMasta
author_rank: Super Contributor
timestamp: December 20, 2017, 09:02:27 pm
content: It seems like a fairly isolated case, but the 1612 has input protection diodes that have gotten in the way of a different design before for me, they will gradually discharge envelope detector/peak hold circuits they are part of. In the case of my design, I just swapped to the OPA1642 - not quite the same spec, but still quite good and available in the same packages/pinouts and very similar in spec.

author: David Hess
author_rank: Super Contributor
timestamp: December 21, 2017, 12:33:30 am
content: As long as the full power bandwidth or slew rate is sufficient for your signal, then the input protection diodes will not be a problem.

author: firstcolle
author_rank: Regular Contributor
timestamp: December 21, 2017, 08:33:24 am
content: many thanks guys!
OPA2182 double amp circuit Gain value question  - Page 1
Forum section: electronics / projects

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 01, 2024, 04:12:13 pm
content: HelloIn the TI doc I have located this circuit base on two OPA2182 for a strain gage bridgeMy question are : this circuit with displayed value is G = 1+ (( 2xRf ) /Rg ) = 401 base on 10K and 50 Ohm resistor1) What is the maximum gain ? I can use as I need 1000 or more ( 1500 ) . Does that will generate other problem as noise ? bandwidth ?2) I suppose that the Rf resistor shall be matched ?Thanks in advanceRegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: June 01, 2024, 04:51:44 pm
content: The Rf don't need to be matched very well. The relevant resistance is the sum of the feedback resistors. A mismatch will give a little common mode signal to the ADC, but usually the ADCs are relatively good with the common mod suppression.High gain limits the bandwidth to GBW / gain. In the shown circuit the 1 µF capacitors in parallel are however more relevant than the amplifier GBW. So a gain of 1000 should be OK - reduce the capacitors if Rfb gets larger. Noise is not directly effected - more by Rg and high gain is more favoring a small Rg - so low gain (e.g. < 20) can be an issue noise wise.Az amplifiers can usually work well with high gain as the open loop gain is large. With more normal OP-amps one may get more nonlinearity.

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 01, 2024, 05:59:04 pm
content: KleinsteinGreat thanks for your quick and accurate answerRegardsOS
OPA541 High-Power-Opamp - Die pictures - Page 1
Forum section: electronics / projects

author: Noopy
author_rank: Super Contributor
timestamp: May 03, 2020, 09:56:38 pm
content: Hi all!Perhaps you are interested in an OPA541 High-Power-Opamp:The highside and the lowside power transistor(s) are huge!It contains a ceramic plate which probably is made of beryllium oxide.See everything here:https://www.richis-lab.de/Opamp02.htmBest regards,Richard

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 03, 2020, 10:30:49 pm
content: Quote from: Noopy on May 03, 2020, 09:56:38 pmDefinitely is, that's what the BeO marking on the cover means.

author: Noopy
author_rank: Super Contributor
timestamp: May 04, 2020, 03:03:00 am
content: Quote from: NiHaoMike on May 03, 2020, 10:30:49 pmMost likely…

author: Noopy
author_rank: Super Contributor
timestamp: May 15, 2020, 09:25:38 pm
content: Since the OPA541 didn´t fill the topic here some pictures of the APEX PA88:https://richis-lab.de/Opamp03.htmLess current (100mA) but much more voltage (+/-250V).It´s a nice hybrid.And of course some die pictures.Does anybody know why they have put a silicon slice (only) under the Lowside-Output-Transistor?Is that because of the p-channel depletion MOSFET? Because of the p in the channel?More pictures on my website.

author: Noopy
author_rank: Super Contributor
timestamp: May 23, 2020, 08:06:43 pm
content: Are you interested in more Power-Opamps?I have an ICH8530 for you:Once more a berryllium oxide substrate.Interesting solder joints...That looks like a crude laser trimming...Nice MESA-transistors!More pictures on my website:https://richis-lab.de/Opamp04.htm

author: Noopy
author_rank: Super Contributor
timestamp: October 31, 2020, 08:13:44 pm
content: Quote from: Noopy on May 15, 2020, 09:25:38 pmA small update to the PA88:In the datasheet all the transistors look like depletion MOSFETs but that´s wrong. The amplifier wouldn´t work probably with depletion mode MOSFETs. I exemplary probed Q8 and it´s a enhancement MOSFET:I assume all the MOSFETs are enhancement MOSFETs.

author: PartialDischarge
author_rank: Super Contributor
timestamp: October 31, 2020, 08:26:13 pm
content: The lightning, sharpness and depth of field of your pictures is amazing. What equipment do you use?

author: Howardlong
author_rank: Super Contributor
timestamp: October 31, 2020, 08:27:45 pm
content: Truly fascinating!

author: Howardlong
author_rank: Super Contributor
timestamp: October 31, 2020, 08:29:07 pm
content: Quote from: MasterTech on October 31, 2020, 08:26:13 pmGood question!Focus stacking maybe?

author: Noopy
author_rank: Super Contributor
timestamp: October 31, 2020, 08:33:59 pm
content: We talked a lot about that here:https://www.eevblog.com/forum/projects/decapping-and-chip-documentation-howto/I use a normal camera with a 10-22mm lens reversed and some distance rings between lens and camera.Then you need the right light and a lot of experience and here we go.The tilted pictures are of course focus stacked. Often I have to take 20 or 30 pictures for one picture.
OpAmp Buffer for IF - Page 1
Forum section: electronics / projects

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: April 12, 2017, 03:24:58 am
content: Any suggestions for an op amp suitable for buffering output from a receiver's IF stage? The IF is around 8.3MHz. Ideally I could use a single supply.Thanks.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: April 12, 2017, 04:54:23 am
content: Great. Thanks for the info.

author: danadak
author_rank: Super Contributor
timestamp: April 12, 2017, 12:47:28 pm
content: JFET source follower quite effective.https://en.wikipedia.org/wiki/File:N-channel_JFET_source_follower.svgRegards, Dana.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: April 12, 2017, 04:28:23 pm
content: The JFET source follower is likely an even better solution for my task.Any specific JFET that is well suited to this task?Thanks in advance.

author: Zero999
author_rank: Super Contributor
timestamp: April 12, 2017, 05:05:31 pm
content: Quote from: FlyingHacker on April 12, 2017, 04:28:23 pmWhat are your requirements? Input, output impedance?The 2N3819 is my usual choice of generic JFET.http://www.onsemi.com/pub/Collateral/2N3819-D.PDF

author: David Hess
author_rank: Super Contributor
timestamp: April 12, 2017, 06:46:07 pm
content: Current feedback operational amplifiers and "video" amplifiers work well at typical IF frequencies. Usually single transistor shunt or transconductance amplifiers are adequate.

author: danadak
author_rank: Super Contributor
timestamp: April 12, 2017, 09:27:03 pm
content: http://www.nutsvolts.com/magazine/article/fet_principles_and_circuits_part_2http://guitarscience.net/calcs/cd.htmRegards, Dana.
OpAmp Buffer input impedance (LM8261) - Page 1
Forum section: electronics / projects

author: BurnedResistor
author_rank: Regular Contributor
timestamp: October 23, 2016, 09:25:27 am
content: Dear All,As part of battery powered project I am working on, I designed a simple analog circuit to take the voltage swing off the battery down to the input range of the ADC in the MCU I am using.The first stage of this is a simple voltage divider, followed by a zener protection diode, followed by an op amp buffer, seeing I did not want the following stages to load down the voltage divider and change the division factor.The schematic is attached.Currently, during board bring up, I first only populated the voltage divider (Only r12 and r12, the other resistors and pot. are there in case I need different division factors), to confirm it was doing what I wanted it to do. This being the first time I am designing such a circuit, I wanted to go slow. As expected, it divides the voltage down by 3. The 12.8V test signal creates a 4.25V level.However when I attach the opamp buffer the voltage drops down to around a few hundred millivolt. I measured the current going into the opamp trough r16, and it is around 0.5 maIs this typical for an opamp? Is there any way I can stop it from loading the divider so much?

author: BurnedResistor
author_rank: Regular Contributor
timestamp: October 23, 2016, 09:33:49 am
content: 1) Ups! Sorry2) Yup just double checked.Thanks for the quick reply:)

author: MattHollands
author_rank: Frequent Contributor
timestamp: October 23, 2016, 12:08:40 pm
content: IN+ and IN- look correct to me for a voltage follower?What looks wrong is the pin numbering according to the LM8261 datasheet1 Output O Output2 V- I Negative Supply3 IN+ I Non-inverting input4 IN- I Inverting Input5 V+ I Positive SupplyMatt

author: BurnedResistor
author_rank: Regular Contributor
timestamp: October 23, 2016, 06:55:54 pm
content: You caught it chaps!Thank you!Time to bust out the mod wire, blade and hakko -.-

author: rob77
author_rank: Super Contributor
timestamp: October 23, 2016, 09:36:47 pm
content: i'm curious how did it happenthe datasheet for LM8261 shows only one pin configuration for SOT23-5 package, so where did the wrong pinout come from ?for example MCP6001 has 3 different pin configurations for SOT23-5 - so it's quite easy to mixup and end-up with the wrong pinout

author: David Hess
author_rank: Super Contributor
timestamp: October 24, 2016, 12:31:00 am
content: The LM8261 has a pretty high uncompensated (*) input bias current which is adding 18 millivolts of error though the 6.7k source resistance. This can be compensated for by using a 6.8k resistor inside the feedback loop.If battery drain needs to be minimized, then higher value divider resistors and a lower input current operational amplifier can be used. I might use an OPA197, TLV379, TLV314, or TLV316 but there are lots of choices.(*) Single supply and rail-to-rail input operational amplifier do not have input bias current compensation.
OpAmp circuit w/offset, Understanding gain resistor values - Page 1
Forum section: electronics / projects

author: Skimask
author_rank: Super Contributor
timestamp: March 12, 2016, 05:48:58 am
content: Youtube video running the Falstad circuit simulator link:https://www.youtube.com/watch?v=EYEqxfH9VHM&feature=youtu.beShould have come out in 720p or better...didn't...don't know why.Trying to understand why the 2 resistors mentioned in the video (both 91K in this case) have to be equal for the offset to work the way I want it to work...eg. 1 volt at the offset input, gives me 1 volt at the offset input.Should I redraw the circuit, place things differently to make a bit more sense?

author: MarkF
author_rank: Super Contributor
timestamp: March 12, 2016, 06:06:06 am
content: Opamp #3 is in a summing configuration.What does the circuit look like to you when you remove Opamp #1 (grayed area)? What is the gain of Opamp #3 in that case?Does that help?

author: Skimask
author_rank: Super Contributor
timestamp: March 12, 2016, 06:14:41 am
content: So #2 doesn't care what the 91K is doing on it's output. Got that.#3 ends up being Av= -1.I guess maybe the better question is...why don't the 10K and 91K on the - input of #3 interact? Or do they and I'm missing it?

author: danadak
author_rank: Super Contributor
timestamp: March 12, 2016, 04:28:57 pm
content: They do not interact because the NI input to the OpAmp is at virtual grounddue to the - feedback placed around the OpAmp, eg. the 91 K from outputback to input.http://www.colorado.edu/physics/phys3330/PDF/Experiment5.pdfRegards, Dana.

author: MarkF
author_rank: Super Contributor
timestamp: March 12, 2016, 07:11:06 pm
content: The 10K resistor on the non-inverting input of #3 is for compensation. Maybe this will clear it up:Inverting Opamp with compensating resistor.

author: Skimask
author_rank: Super Contributor
timestamp: March 13, 2016, 05:43:45 am
content: Yes, now I understand. Virtual ground at the - input. The resistor on the + input also makes sense now.Thanks for the quicky lesson.
Opamp controlled current source calulations - Page 1
Forum section: electronics / projects

author: broodtrommeltje
author_rank: Newbie
timestamp: January 31, 2024, 11:05:29 am
content: I'm working on a project that aims to test LED degradation over time by controlling the current passing through it, I attached a schematic of the concept.The setup involves a voltage controlled current source using an N-FET, which is regulated by an opamp and controlled by a DAC.Details:The DAC feeds into the positive input of the opamp as differential amplifier, the opamp output controls the gate of the N-FET. Feedback of the output current is measured through the voltage over R1.D2 is placed to prevent current to flow when the DUT (LED and voltage) is connected in reverse.Note: in the simulation, I've replaced the LED with a voltage source to get the voltage drop over the LED.The circuit shown works perfectly in the simulation and on a breadboard, however I'm trying to understand the theoretical side of the circuit. But I'm stuck calculating the current as a function of the DAC voltage. Can anyone guide me on how to calculate the output current?

author: KerimF
author_rank: Frequent Contributor
timestamp: January 31, 2024, 11:48:27 am
content: Quote from: broodtrommeltje on January 31, 2024, 11:05:29 amAt the opamp inputsV(IN+) = V(out)*R4/(R4+R3) + V(V_DAC)*R3/(R4+R3)V(IN+) = (V(out)*R4 + V(V_DAC)*R3)/(R4+R3)V(IN-) = V(+15)*R5/(R5+R2)ButV(IN+) = V(IN-)(V(out)*R4 + V(V_DAC)*R3)/(R4+R3) = V(+15)*R5/(R5+R2)And sinceR4+R3 = R5+R2V(out)*R4 + V(V_DAC)*R3 = V(+15)*R5Also, sinceR5 = R4V(out)*R4 + V(V_DAC)*R3 = V(+15)*R4V(out)*R4 + V(V_DAC)*R3 - V(+15)*R4 = 0R4*(V(out) - V(+15)) + V(V_DAC)*R3 = 0V(+15) - V(out) = V(V_DAC)*R3/R4ButV(+15) - V(out) = I(R1)*R1ThereforeI(R1)*R1 = V(V_DAC)*R3/R4I(R1) = V(V_DAC)*R3/R4/R1
Opamp current buffer - Page 1
Forum section: electronics / projects

author: Johntron
author_rank: Contributor
timestamp: September 16, 2015, 02:10:58 pm
content: I've designed a voltage buffer using an opamp like so:Current varies between the output and input circuits, but voltage is mirrored (unity gain).How would I do the opposite with an opamp: a current buffer where voltage varies, but current is mirrored?I know opamps have near-infinite input impedance and near-zero output impedance, so I'm not sure it's possible.A diagram would be awesome.

author: dom0
author_rank: Super Contributor
timestamp: September 16, 2015, 06:18:18 pm
content: AKA current mirrorhttps://en.wikipedia.org/wiki/Current_mirror#Feedback_assisted_current_mirrorAs you might see from the schematic it's just the classic op amp current source with low input impedance (current instead of voltage input).

author: Fank1
author_rank: Regular Contributor
timestamp: September 16, 2015, 10:46:20 pm
content: You are in fact reading current with this circuit.Because you have a fixed load, the 10 K resistor, the current is simply the voltage divided by 10k.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: September 16, 2015, 11:29:29 pm
content: for high impedances you can often use the op amp in a inverting amplifier configuration with only 1 resistor to make a IV converter.You can haveIVVIIIVV

author: Johntron
author_rank: Contributor
timestamp: September 17, 2015, 01:27:50 am
content: @dom0 ah. So the opamp can't do it by itself - transistors are required? I see how that makes sense, but was looking for a definitive answer in case I'm missing something.Thanks! I've scrolled past that diagram multiple times, but never noticed the opamp.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 17, 2015, 05:47:01 am
content: The traditional op-amp is a voltage type. Meaning: the output is constant voltage, and the input-to-output characteristic is very high voltage gain and very low input current (at DC, that is).A current type amp wouldn't be terribly hard to make or use, but I don't think it exists as a product. There are "current mode op-amps", but these are current input only; they still deliver output voltage (so exhibit very high transconductance, instead of dimensionless voltage or current gain). So you're kind of left making a half-assed one out of transistors and op-amps.Tim

author: Johntron
author_rank: Contributor
timestamp: September 17, 2015, 05:59:09 am
content: Perfect, thanks Tim!

author: Phoenix
author_rank: Frequent Contributor
timestamp: September 17, 2015, 07:15:56 am
content: You can get operational transconductance amps, that convert a differential voltage into a current e.g. LM13700. That's almost what you want...https://en.wikipedia.org/wiki/Operational_transconductance_amplifier
opamp dc buffer - Page 1
Forum section: electronics / projects

author: lincoln
author_rank: Regular Contributor
timestamp: September 11, 2014, 06:21:27 pm
content: Hello,I am working onThehttp://m.eet.com/media/1126947/11805-view_download_the_schematic_featured_in_the_clip_pdf_.pdf]original design (PDF) has some features that I'm not interested in so I have simplified it some what. So far I have sourced a 10K Kelvin Varley divider and prototyped.The issue is that I am seeing an voltage offset out of the buffer. If I tie the non inverting input of the lt1881 to ground I see a vout of -19uV. Tying the non inverting input to ground through a 10K and 1M resistors, the output goes to 12uV and 87uV respectively. Are these reasonable numbers for the lt1881? The numbers for 0 and 10 K ohms look reasonable but I cant explain the 87uV for 1meg. This makes me think I am doing something wrong. This is after washing the flux from the board.Realistically the max input impedance is 10K and the offset voltage in this range is acceptable but if there is some thing i'm getting wrong i would like to correct it.Thank you,Link

author: Artraze
author_rank: Contributor
timestamp: September 11, 2014, 07:37:37 pm
content: The LT1881 has aninput offset voltageof ~30uV typical, so -19uV is well within spec.Similarly, the input bias current is ~100pA, so that through a 1M resistor would give an additional 100uV offset, which is pretty much what you're seeing.So all in all what you're seeing is about what one would expect to see for a LT1881. It's maybe not the greatest device, but the design is only meant for 10V to 5 decades, which means a basic uncertainty of +/-50uV so it'll certainly do the job.

author: David Hess
author_rank: Super Contributor
timestamp: September 12, 2014, 09:38:33 am
content: The LT1881's CMRR and PSRR could add up to another 6 microvolts per volt of offset error as well.The LT1881 is a good choice for this. It looks like Linear Technology took their LT1008/LT1012/LT1097 series and added a rail-to-rail output stage. I wish they had included a schematic in the datasheet.

author: lincoln
author_rank: Regular Contributor
timestamp: November 13, 2014, 06:22:38 am
content: Well after months of procrastinating I hit send on the Gerber files. Looks like the internal routing didn't make it through the export, opps. here is the first board fixed:

author: lincoln
author_rank: Regular Contributor
timestamp: November 13, 2014, 08:45:15 pm
content: Well, f^&*, put it together, probalby should have soldered it in stages, the board trips current limit on the power supply. Anyway, reference is beautiful. Dekapot is fantastic.link

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 13, 2014, 09:09:08 pm
content: OK, what's a "Tecktronics"?

author: lincoln
author_rank: Regular Contributor
timestamp: November 13, 2014, 10:12:55 pm
content: this:plus this:EEVblog #480 - 300MHz Owon SDS Oscilloscope

author: LukeW
author_rank: Frequent Contributor
timestamp: November 14, 2014, 12:17:04 am
content: Wow, for a second there I thought that was a new leader in the cheap Wun Hung Lo DSO market.
OpAmp for high-Q inductor in ultra-narrow band notch filter in controller applic - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: December 20, 2019, 05:06:48 am
content: Hi all,I'm trying to filter out a "single" frequency (200 KHz). i.e. a ultra narrow band pass filter. It works quite well using a simple high-Q LC filter but with the inductor and capacitor tolerances it is hard to tune it to that exact frequency and I need it to be very precise. I have a microcontroller on the board so ideally I want to be able to tune it for the highest amplitude.I know that op-amps can replace inductors. So I think I should be able to adjust (through a digital pot) the resistor in the op-amp circuit that simulates/replaces the inductor.Would such solution work?Can I get a very high-Q response by replacing the inductor with a op-amp circuit?If yes, how?Many thanks

author: awallin
author_rank: Frequent Contributor
timestamp: December 20, 2019, 05:40:22 am
content: the notch center frequency might help here... kHz, MHz, GHz ??

author: dzseki
author_rank: Frequent Contributor
timestamp: December 20, 2019, 06:37:53 am
content: Also if you exactly know what you are looking for consider lock-in amplification instead of high-Q filtering.

author: ricko_uk
author_rank: Super Contributor
timestamp: December 20, 2019, 07:29:29 am
content: Hi Awalling,200 KHz is the Frequency.Thank you

author: ricko_uk
author_rank: Super Contributor
timestamp: December 20, 2019, 07:31:47 am
content: Thank you Dzseki,I googled for hours to find a lock-in amplifier IC or schematic but couldn't. Do you have any pointers for a simple solution?As I mentioned in the reply above the carrier freq is 200KHz and I do have the original clock available on the board as sinewave (I can also make it square wave).Many thanks

author: Kleinstein
author_rank: Super Contributor
timestamp: December 20, 2019, 08:53:49 am
content: The OP based filters usually need an OP GBW well higher than frequency times Q value. So a high Q at 200 kHz is not very practical with an active filter. Here an LC filter is probably better. If needed one could tune it with vari-cap or so.There could be an option to use a kind of synchronous notch. Some AZ OPs use this method internally, so the corresponding literature could help here.Is a really narrow notch really needed ? If it is only about getting a deep notch one could use 2 in series.

author: thm_w
author_rank: Super Contributor
timestamp: December 21, 2019, 12:50:40 am
content: Are you talking about a bandpass filter or a notch filter?https://www.ti.com/lit/an/slyt235/slyt235.pdf

author: nctnico
author_rank: Super Contributor
timestamp: December 21, 2019, 12:53:01 am
content: What does the circuit do? Why do you need to filter the 200kHz signal?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 21, 2019, 01:24:48 am
content: Also, a PLL, which can be analyzed in terms of a bandpass filter.Tim

author: ricko_uk
author_rank: Super Contributor
timestamp: January 02, 2020, 04:24:55 am
content: Thank you T3sl4co1l,that sounds interesting. How? Where can I find infos on how to do that?Thanks
opamp input diff voltage spec - Page 1
Forum section: electronics / projects

author: sandy
author_rank: Contributor
timestamp: August 06, 2014, 03:34:38 pm
content: Hi, can somebody help me finding "max I/P diff voltage " forhttp://www.linear.com/product/LTC6084. Rgds

author: LvW
author_rank: Frequent Contributor
timestamp: August 06, 2014, 04:22:48 pm
content: The max. input voltage (linear range) depends, of course, on the closed-loop gain (due to feedback).The open-loop gain is larger than Aol=100dB. That means, theoretically (and neglecting offset) for a dual voltage supply with 10V the allowed input diff. voltage without feedback is app. 10V/1E5=1E-4V=100µV (assuming Aol=100 dB).

author: void_error
author_rank: Frequent Contributor
timestamp: August 06, 2014, 04:33:33 pm
content: According to the datasheethttp://cds.linear.com/docs/en/datasheet/60845fa.pdfit's V+-V-. In other words it's the supply voltage.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: August 06, 2014, 04:38:58 pm
content: the +/-10 mA abs max spec pin current spec should also be observed - CMOS inputs (most other op amp types too) will have ESD diodes to the rails and the current through the diodes needs to be limited by series R if Vsource can be above the op amp Vsupply (like when the Vsupply is 0)

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2014, 05:30:28 pm
content: The datasheet does not specify the maximum differential input voltage but I believe this is because it is the same as the common mode input voltage range. Both are limited by the ESD protection diodes to a value lower than the gate oxide breakdown voltage of the CMOS process used.
Opamp placement for best noise/interference performance - Page 1
Forum section: electronics / projects

author: Dan Moos
author_rank: Frequent Contributor
timestamp: April 29, 2016, 02:32:03 am
content: Ok, I think I know the answer here, but I want some affirmation or correction. Apologies to those that helped with a similar question earlier. I still need clarification i guessI have a design that uses a crosspoint switch chip (AD75019) to distribute audio signals, some of which are relatively high gain (guitar pedal signals to be exact)I plan to use opamp buffers (t074's) every where the signals enter and exit the switching chip. There will be a main PCB withe the switching chip and the MCU, and a sub board with the signal jacks on it. I currently plan to use screw terminals to join the signal lines to the main PCB, which will be on individual shielded cables to the board with the jacks.Ok, I feel which end of the signal wires I place the buffers is key to good noise/interference performance. My intuition says that the lines going IN to the buffers should be as short as possible, so the opamps should be close to the input jacks for signals entering the device (ie, on the jack board), and the lines where a signal leaves the switch chip to a buffer should also be short, so for signals exiting the device, the opamp should be close to the switching chip.In other words, any line going into the high impedance input of a buffer should be short in order to reduce noise/interference.Is my thinking correct?My reasoning for wanting the buffers is that the impedance of the switch chip inputs/outputs is apparently pretty dependent on signal level. My current breadboard setup works much better with the buffers in place, but when the gain levels in the pedal signals is high, there is a lot of noise, especially noise from the LCD digital signals. I realize alot of this is grounding and power, not to mention alot of cheap breadboard jumpers, but I still want to be sure my bases are well covered when I make the PCBs. The PCBs will be DIY, so I can afford a few bad designs, but still don't want to waste my copper clad board supplies making unnecessary duds.

author: moffy
author_rank: Super Contributor
timestamp: April 29, 2016, 03:49:40 am
content: Correct. The high impedance input should be as close to the signal source as possible. Gives then a low impedance output which is less susceptible to interference.

author: TiN
author_rank: Super Contributor
timestamp: April 29, 2016, 04:48:16 am
content: Once you done layout, you can post it here and lot of people may come and help you out.Analog devices and TI have nice public appnotes and handbooks regarding opamp layout and placement questions, be sure to check those out. Most of basics and design approaches are covered well there.
Opamp Spice Simulation - Clamping - Page 1
Forum section: electronics / projects

author: bruxillensis
author_rank: Newbie
timestamp: April 15, 2025, 04:26:39 pm
content: Hello, first time trying a post.I am designing a TEC driver and have been attempting to simulate the schematic in Altium with spice models. Everything is mostly okay, but I am having trouble with simulating opamps in the circuit correctly. The opamp I need to use for the design environment is the LTC2054, but since its implemented with proprietary code, I cant use the LTspice model. Instead I have tried to use physical models of different opamps with similar specs. I have also tried the ideal opamp models built into Altium. When I run Operating Point or DC Sweep simulations, I find the opamp output can be beyond the range of VCC and VEE. Is clamping not typically captured in these models? Is there another reason for this related to the simulation I have chosen? I've attached an image of the schematic, which should should the output of U4 to be -1.880V, where VEE is 0V, and the output of U3 is 10.93V where VCC is 10V.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 15, 2025, 04:42:42 pm
content: Hi,Have you considered using LTspice?I will make you a deal. If you commit to trying LTspice, I will draw your schematic in LTspice for you.Regards,Jay_Diddy_B

author: bruxillensis
author_rank: Newbie
timestamp: April 15, 2025, 05:06:37 pm
content: I've considered it of course and I am willing to do so if that were to solve the problem, but I suppose I would like to make sure it's a) unexpected/incorrect behaviour and b) not my own error before redoing the schematic again in another software hoping for a different result.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 15, 2025, 05:41:21 pm
content: Hi,Here is a test to show that the LTC2054 clips close to the rails in LTspice:The green trace is Vin, the red trace is the LTC2054 output.This circuit needs the LTC2054HV if the rail is 10V.I have attached the LTspice circuit .ascRegards,Jay_Diddy_B

author: bruxillensis
author_rank: Newbie
timestamp: April 15, 2025, 06:13:23 pm
content: Thanks Jay_Diddy_B,Recreating a test circuit in Altium confirmed it does not seem to be modelling the correct behaviour. Should have tried that first.Best,bruxillensis

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 16, 2025, 12:33:41 am
content: Hi,Here is the original circuit drawn in LTspice:I have attached the LTspice .asc file.It doesn't seem to work as drawn.Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: April 16, 2025, 01:09:08 am
content: Hi,I made a few adjustments.This is a version that works a lot better.Jay_Diddy_B
opamp to transformer input mod. - Page 1
Forum section: electronics / projects

author: mkiijam
author_rank: Regular Contributor
timestamp: July 01, 2024, 02:06:48 am
content: I'm thinking about replacing the 4 input caps with a transformer just for fun / experimentation on this circuit (GSSL.)Should I ground the Secondary low or run both sides of the transformer into the NE5534? Do I need the 22k's? BTW, the "DBX202C" is actually a THAT2180

author: moffy
author_rank: Super Contributor
timestamp: July 01, 2024, 02:58:26 am
content: You could try both to see which gives the best performance, quite possibly no difference, but I would lean towards grounding one side of the transformer output. The '22k' depend on the output impedance of the transformer, quite possibly you could lower the value as you are no longer providing an RC high pass filter and reduce the input noise.
Opamps free to a good home - Page 1
Forum section: electronics / projects

author: Sengcid
author_rank: Regular Contributor
timestamp: February 19, 2024, 03:15:14 pm
content: Large number of DIL op-amps (+ sockets) free to a good home. Mainly LF356/LF357 but also good DC (e.g.OP77) and fast (OP797 and OP37) and a few INAs. Please PM if interested, preferably mainland GB – post brexit paperwork a nightmare.
Open circuit voltage at the input to the 4 - 20mA loop - Page 1
Forum section: electronics / projects

author: IconicPCB
author_rank: Super Contributor
timestamp: February 29, 2016, 03:47:56 am
content: What might be the range of open circuit voltages in a 4-20mA receiver?

author: IconicPCB
author_rank: Super Contributor
timestamp: February 29, 2016, 04:22:46 am
content: Seems the answer is anyone of folowing 12, 15, 24, 36V while the older units may be operating at voltages higher than 36V.

author: Rerouter
author_rank: Super Contributor
timestamp: February 29, 2016, 06:30:12 am
content: common industrial supply voltage is 24V, however most controllers and similar support up to 48V on the input, 48V is generally the highest you will see,

author: dwpatter53
author_rank: Contributor
timestamp: March 01, 2016, 10:20:27 pm
content: If the 4-20 mA loop has a loop powered device, that devices minimum voltage will determine the minimum voltage.The most common supply voltage in industrial instrumentation and process control is nominally 24 VDC.Actual voltage can range up to 26-28 VDC.
Open Distributed Device Modules - Page 1
Forum section: electronics / projects

author: tomgat
author_rank: Regular Contributor
timestamp: February 10, 2023, 09:21:24 pm
content: So I need to design a stackable module design for a industrial sector project, and was thinking if I was going down this path, why not make it an open design. At a top level what I need is what commercial offerings (AB,B&R, Siemens, etc) already do in that you plug in a collection of IO modules (Inputs/Outputs/ADCs/DAC/Encoders/etc) with different purposes in a chain, and then a master microcontroller automatically detects each module and their location. I cant seem to find any of the commercial offerings that are open, and was curious if anyone has seen anything like this. If not, do you think something like this should exist? (example: SparkFun has Qwiic which is horribly deficient for several reasons, and Mikroe has MikroBus isnt chainable)As a first thought.. On the hardware side, I was thinking of each module having a cheap, small, and fast microcontroller (RP2040?) that are preprogrammed and whose only purpose is to identify each module and then relay the other modules communications back to the master controller. Any thoughts or ideas would be appreciated.

author: redkitedesign
author_rank: Regular Contributor
timestamp: February 13, 2023, 11:41:33 am
content: Start with some design limitations.- How many devices on the bus- How much communications (bandwith and latency)- Hot pluggable or not- Powered independently or centrally?There are some simple basics. RS422 only requires 2 wires, and is reasonably robust against broken/unpowered devices on the busCAN has tons of support from automotive but is less robustBoth can do discovery with the appropriate software.If you need to discover the physical order of the bus you'll probably want some ring-like bus, where each device passes a message to the next (and thus can add its name to the discovery order). However, those are hard to protect against a single broken device in the chain. You can add some resilience by making the chain a bi-directional ring (so all devices behind the broken one can be reached form the other side)If you will only have about 10 devices, you might want to use a simple 4-bit addressing scheme. Do some clever bit swaps/inversions in each module, and each module sees 0b0001 when addressed.You can combine methods: A RS422 bus for communications, and a single bit neighbour-to neighbour interface that can be controlled through RS422 to discover the order.
Open interface chest heart rate monitoring straps? - Page 1
Forum section: electronics / projects

author: abhishekkumar1902
author_rank: Regular Contributor
timestamp: January 29, 2018, 06:16:34 pm
content: Any idea about any of these kinda chest heart rate monitoring straps which can be openly connected to a BLE/Classic-BT device for data acquisition?

author: Bud
author_rank: Super Contributor
timestamp: January 29, 2018, 07:03:37 pm
content: What is your question?

author: abhishekkumar1902
author_rank: Regular Contributor
timestamp: January 30, 2018, 05:59:00 am
content: I just wanted to know if there are chest heart rate monitoring straps available in the market which can be openly connected to a BLE/Classic-BT device for data acquisition? I mean it seems like heart rate straps from POLAR, GARMIN, ZEPHYR, etc run on proprietary protocols and we cannot interface them directly to something like arduino, etc.

author: Bud
author_rank: Super Contributor
timestamp: January 30, 2018, 02:20:49 pm
content: I see. Not to my knowledge, but maybe browsing Banggood or Aliexpress may find something.

author: Cerebus
author_rank: Super Contributor
timestamp: January 30, 2018, 05:10:05 pm
content: There are three RF interfaces commonly used for these chest strap heart rate monitors:Bluetooth (normally BLE) - not very common but there are some out there - tend to be relatively expensive. There's a Bluetooth profile for these devices - check out the Bluetooth standards.ANT+ - a radio standard targetted at sports/exercise equipment in general. There's an industry association athttps://www.thisisant.com/and openly available documentation. Nordic Radio make a specific chipset for this and I suspect that is what is used by 99% of designs out there.5kHz RF/induction standard. This is simply the actual detected heart pulses (R wave) squared up and modulated onto a 5kHz or 5.6kHz carrier. Easy to interface to with just a pickup loop, amplifier and a PLL based tone decoder like the LM567 or similar. Originally used by Polar, common on the cheapest 'no name' brands. There is a later variant with a coding burst as well, that allows you to differentiate between a small set of heart rate monitors operating close to each other.I built a receiver for the last standard using an old transistor radio rod antenna as the pickup coil, an LM358 as amplifier and an LM567 - specifically to link to an Arduino. Worked fine with no real design effort - essentially I worked directly off the LM567 datasheet and breadboarded it as I designed it in my head/on a scrap of paper. It really is that simple, so I've not got an actual schematic to offer.

author: abhishekkumar1902
author_rank: Regular Contributor
timestamp: January 31, 2018, 06:51:47 pm
content: Great info, thanks
Open source 12V 4.3A switch mode power supply - Page 1
Forum section: electronics / projects

author: j57H8I4
author_rank: Contributor
timestamp: December 28, 2016, 09:59:16 pm
content: I am new to electronics. I recently tried to repair a 12V 4A switch mode power supply, but I had to give up because I could not test or replace smd capacitors, as there is no indication of their values. So I have thought to create a project to realize an open source 12V 4.3A switch mode power supply. I have choosed to use the software Kicad to develop the project, so I have inserted the link to the files that Kicad created. I do not know even how to start the electrical scheme, so if someone would like to contribute, could start the electrical scheme.I am not interested only in realizing the power supply, but I am interested even more in learning electronics, so if you could explain what you do on the project I would appreciate that very much.https://drive.google.com/drive/folders/0B6ejIS6kTJNLbE5BQ1RtcVN1TG8?usp=sharing

author: jaromir
author_rank: Unknown
timestamp: December 29, 2016, 06:07:20 am
content: You can increase your chances of somebody reviewing your design if you upload it in some "easy to read" format, like pdf of some bitmap format (png, gif), at least the schematics. A lot of people don't have kicad installed or want to view it on tablet/phone.