hybridfree/eevblog-posts huggingface dataset:
Opamp adjustable gain  - Page 1
Forum section: electronics / beginners

author: anishkgt
author_rank: Frequent Contributor
timestamp: September 28, 2017, 11:34:05 pm
content: I wish to have a variable gain to pin 5 for the schematic . With a constant gain it would be a resistor between pin 5 and R4. Would R23 a give a variable gain. Is the schematic correct ?

author: Zero999
author_rank: Super Contributor
timestamp: September 29, 2017, 12:02:31 pm
content: Yes, that will give a variable gain, but keep the leads to the potentiometer as short as possible.Could you have make the schematic any more difficult to read? Please use proper op-amp symbols. It makes the circuit much easier to understand.

author: anishkgt
author_rank: Frequent Contributor
timestamp: September 29, 2017, 12:05:31 pm
content: Thanks hero.It does confuse me as well. Got the symbol from Digi-Key with the product.Quick question,Are all opamp symbol and pin the same ? I guess not, does everyone create their on when working different opamp ?Www.Georgehobby.wordpress.comEquipments: DSO104z, Hakko FX888D

author: Zero999
author_rank: Super Contributor
timestamp: September 29, 2017, 12:10:52 pm
content: Op-amp symbols are generally the same and there's a standard pin-out for single, dual and quad op-amp ICs, which is followed by most manufacturers, but always check the data sheet to be sure.
opamp amplificator - Page 1
Forum section: electronics / beginners

author: yalect
author_rank: Regular Contributor
timestamp: December 31, 2016, 12:36:38 pm
content: Hello,I would like to ask you, can we built opamp amplifiacator with LM741 without GND? like in the follow video of radio circuit, I think there is no GND or 0Vthank you

author: Zero999
author_rank: Super Contributor
timestamp: December 31, 2016, 12:54:50 pm
content: Quote from: yalect on December 31, 2016, 12:36:38 pmIf you watched the video through to the end, then you'll see it does have a 0V/GND rail.It's not a very good circuit. The op-amp is not biased properly and demodulation is performed using the PN junctions on the op-amp inputs.And as far as taking only a minute to make, yeah right? That hand wound coil certainly took a lot longer than a minute to make.

author: LvW
author_rank: Frequent Contributor
timestamp: December 31, 2016, 02:20:33 pm
content: It's not a very good circuit. The op-amp is not biased properlyIt`s even worse - the inverting opamp node is floating and there is POSITIVE feedback.

author: ebclr
author_rank: Super Contributor
timestamp: December 31, 2016, 03:45:40 pm
content: You can make a virtual ground, just use 2 resistor of 10K or 1k atached one to +Vcc and other the -vcc, and use the midle of those resistor as your ground.Here a easy wayhttps://www.aliexpress.com/item/FM-Stereo-Radio-Module-RDA5807M-Wireless-Module-Profor/32667681720.html?spm=2114.01010208.3.18.Hkvjin&ws_ab_test=searchweb0_0,searchweb201602_2_10065_10068_10000009_10084_10083_10080_10082_10081_10060_10062_10056_10055_10037_10054_10033_10059_10032_10099_10078_10079_10077_426_10103_10073_10102_10096_10052_10050_10107_10106_10051,searchweb201603_2,afswitch_5&btsid=2cf3f8b0-6144-4a7f-a955-53bb1afab08b

author: Audioguru
author_rank: Super Contributor
timestamp: December 31, 2016, 06:31:28 pm
content: The input pin numbers of the opamp are shown backwards. Pin 2 is the inverting input and pin 3 is the non-inverting reference voltage input that has no voltage.

author: yalect
author_rank: Regular Contributor
timestamp: December 31, 2016, 06:43:33 pm
content: If we romove the GND or 0 no connection will work?Thank you

author: Zero999
author_rank: Super Contributor
timestamp: December 31, 2016, 06:45:54 pm
content: Quote from: yalect on December 31, 2016, 06:43:33 pmNo, you need a complete circuit for a current to flow, so it won't work if the 0V connection is removed.Oh and the correct English term isamplifier.
Opamp amplifier 0-5V to -1.2-24V - Page 1
Forum section: electronics / beginners

author: IrejectYourReality
author_rank: Contributor
timestamp: August 22, 2016, 05:34:47 pm
content: Hi guys, just a quick question, I need an opamp circuit, that would take 0-5V at the input and produce -1.2-24V at the output. I have a negative voltage supply and a 1.2V voltage reference. Would this circuit do the trick?Or do I need something different?

author: Zero999
author_rank: Super Contributor
timestamp: August 22, 2016, 08:35:42 pm
content: No it won't work, see the following guide linked below:http://www.ti.com/lit/an/sloa097/sloa097.pdf

author: w2aew
author_rank: Super Contributor
timestamp: August 22, 2016, 08:48:43 pm
content: This can easily be done with a summing amplifier to combine the DC offset you need with the amplified signal path. Here's my tutorial on the op amp based summing amplifier...
Opamp basics - electret mic peak detector - Page 1
Forum section: electronics / beginners

author: Zbig
author_rank: Frequent Contributor
timestamp: November 05, 2013, 01:51:40 am
content: Hi everyoneI was looking for a solution for an electret microphone amp/peak detector and came acrossthisWhile I think the guy has made a great job at explaining this, I'm not sure I properly understand why he has intentionally introduced a DC offset on U1 by using virtual ground equal to Vcc/2 (), an offset he has to cancel later on. Is it because the microphone signal could swing below ground or above Vcc (or could it? I'm not sure) otherwise? Or maybe it's there to bias the D3 diode above its Vf so the signal doesn't have to "shoot through" it, i.e. detector isn't effectively limited to V > 0.6V?I'd appreciate any help in understanding this.

author: w2aew
author_rank: Super Contributor
timestamp: November 05, 2013, 02:30:08 am
content: Quote from: Zbig on November 05, 2013, 01:51:40 amIt's mainly because many op amps, like the LM324 he showed) have an input common mode range that does NOT include the supply rails. In other words, the voltage at the input must be between the supply rails.For more info on this, see my video on this topic:

author: Zbig
author_rank: Frequent Contributor
timestamp: November 05, 2013, 11:49:31 am
content: That is a great tutorial, thank you!

author: w2aew
author_rank: Super Contributor
timestamp: November 06, 2013, 02:38:40 am
content: Quote from: Zbig on November 05, 2013, 11:49:31 amThanks. Since the topic was on a peak detector, you might also enjoy this video that I put together:

author: Zbig
author_rank: Frequent Contributor
timestamp: November 06, 2013, 05:36:32 pm
content: I certainly did, thanks!
OpAmp Buffer inputs not at same voltage - Page 1
Forum section: electronics / beginners

author: Alemarius Nexus
author_rank: Newbie
timestamp: March 13, 2015, 06:31:39 pm
content: Hi,I'm fairly new to electronics and trying to get a simple OpAmp-based circuit to work. It's a circuit to determine the ratio of two resistors, R2 and R3. Here's the circuit simulated in LTspice:This is how I want it to work. The voltage at net1 should drop linearly as the resistance of R2 increases (and as R3 drops, because R2+R3 = 1kOhm), but only up to a certain threshold, 300mV in this case. It all looks great in the simulation, but I've built it up on a breadboard with an LM324 from TI and found that the lower voltage threshold is more like 800mV. I've measured it and found that the OpAmp output voltage is at 800mV, although the non-inverting input is at 300mV. How can that be? I thought OpAmps keps their inputs at the same voltage, so the output should be 300mV too in that case. It seems to have something to do with the circuitry behind the output: If I remove the connection from R2 to the positive terminal of the voltage source, I do get my 300mV. I thought the OpAmp output voltage is (relatively) independent of the load at the output pin? That's why I wanted to use an OpAmp in the first place.Any ideas?

author: Andy Watson
author_rank: Super Contributor
timestamp: March 13, 2015, 06:45:30 pm
content: Figure 11, page 9http://www.ti.com/lit/ds/symlink/lm124-n.pdfSuggests that is the correct operation of this amplifier. The output can only pull down to about 700mV. To get lower, the load must be less than 50 microamps.
OpAmp buffer with input tied to ground, behaviour I don't understand - Page 1
Forum section: electronics / beginners

author: Skippy
author_rank: Contributor
timestamp: September 25, 2014, 05:52:45 pm
content: So I was playing with some TI TL062 opamps and found something I didn't understand. If I configure them in a buffer configuration as shown on the left on the below picture if I put in 4.5 V by using a voltage divider, I get 4.5V out, which is what I expecting. But if I connect the non-inverting input to ground, instead of getting 0V on the output, I get around 7V (as shown on the right hand picture). Why is this?

author: c4757p
author_rank: Super Contributor
timestamp: September 25, 2014, 06:07:09 pm
content: You're not allowed to feed it a voltage outside a certain range (common-mode input range); it throws out the bias in the internal circuitry.

author: ConKbot
author_rank: Super Contributor
timestamp: September 25, 2014, 06:26:57 pm
content: With +/- 15V rails, the common mode range extends 'typically' from -12 to + 15V on the TL-062, so they dont like getting close to the V- rail. Put a pot in instead of a divider and see where the output no longer follows the input. It could be proportional to the input, or it could be set at a fixed voltage above the V- rail.And if you drive them out side of their common mode range far enough, some amplifiers will invert on the output. Hence 7V on the output instead of close to 0V.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: September 25, 2014, 06:33:59 pm
content: That particular characteristic of some opamps is called "phase inversion". Fromhttp://www.analog.com/library/analogdialogue/anniversary/6.html,"A common problem encountered with JFET op-amps is phase inversion. If the input common-mode voltage of a JFET op-amp approaches the negative supply too closely, the inverting and non-inverting input terminals reverse functions. Negative feedback becomes positive feedback and the circuit may latch up. This latchup is unlikely to be destructive, but power may have to be switched off to correct it."Generally, opamps billed as "rail to rail input" will not exhibit this behavior (but they still don't actually remain accurate at the supply voltages.)

author: dentaku
author_rank: Frequent Contributor
timestamp: September 25, 2014, 10:43:26 pm
content: I love simple educational posts like this.

author: LvW
author_rank: Frequent Contributor
timestamp: September 26, 2014, 11:13:24 am
content: OK - because dentaku loves simple educational posts - here comes my (simple) explanation:Operating an opamp in it`s linear range using single supply requires a dc output somewhere in the middle of the supply voltage.For this purpose we have a voltage divider (as shown in the most left circuit) biasing the non-inverting input with Vdd/2.Because of unity feedback (gain of +1) this bias voltage also appears at the output - as desired.This explains the necessity of the voltage divider.(I don`t know inhowfar the term "phase inversion" comes into play for this question.)
Opamp configuration question - Page 1
Forum section: electronics / beginners

author: danils
author_rank: Contributor
timestamp: April 12, 2025, 01:41:48 pm
content: Hi all,A friend submitted me this circuits.Output of the filter stage U5C and its network is a sine wave from an accelerometer. Output of U5D (pin 14) is a square wave. It is after applied to the input of a MCU timer peripheral in capture mode for frequency measure.Operation is single supply 3.3V and Vref is Vd/2 = 1.65VIt looks like U5D and its network act like a comparator but I never saw this configuration before. Could anybody be so kind to point me in the right direction to understand its operation? I was unable to find information online and in my books.BTW the operation is not ideal because it looks that the rising edge of the square wave is correctly aligned with the neg-to-pos zero crossing of the sine wave, but the falling edge has a delay relative to the pos-to-neg zero crossing. This delay varies with the sine wave amplitude. (Refer to the oscilloscope picture attached. Frequency is 19.44 Hz. C1 is the filter output - C2 is the comparator output - C3 is the signal input from the AWG and there is a 11x gain stage before the filter)So it looks like a poor-performing comparator. But I'd like to understand its operation and why the original designer implemented this solution.Many thanks!D.

author: Benta
author_rank: Super Contributor
timestamp: April 12, 2025, 03:17:25 pm
content: It's called a "data slicer" or "signal slicer". Do a search.
opamp current to voltage converter - Page 1
Forum section: electronics / beginners

author: shiva kumar
author_rank: Newbie
timestamp: February 17, 2017, 08:29:18 am
content: I have a signal that is 5mA rms. I need to convert this to 5V with a DC bias which has to be given to the arduino ADC. I need your help in designing a simple opamp circuit that can do the followingconvert the 5mA RMS signal to 5V peak to peak with a DC offset such of 5V.

author: Zero999
author_rank: Super Contributor
timestamp: February 17, 2017, 09:57:14 am
content: QuoteI wouldn't recommend that. It would give you a 0 to 10V volt output, which is too high for the ADC. You need 5V peak to peak with an offset of 2.5V.Quote from: shiva kumar on February 17, 2017, 08:29:18 amWhere is the 5mA signal coming from?Is it purely AC? I.e. no DC bias on the current signal?If so and the input impedance doesn't need to be really low, this could be done passively with a couple of resistors, forming a potential divider, and a capacitor.5mARMS= 5*2*20.5= 14.14mAP-PWe want to scale that to 5V peak to peak, which can be done with a resistor:R = V/I = 5/0.01414 = 353.55If we use a potential divider and a 5V supply to bias it around 2.5V, then the resistor values need to be doubled, as the input impedance is equal to both resistors in parallel. R = 353.55 * 2 = 707R1

author: danadak
author_rank: Super Contributor
timestamp: February 17, 2017, 01:29:24 pm
content: Here is a tool you can use to calc vales to generate offset and handle the AC input signal.http://masteringelectronicsdesign.com/differential-amplifier-output-common-mode-voltage-calculator/Regards, Dana.
Opamp feeding opamp on different PCB's - best way to do this? (Schematic shown) - Page 1
Forum section: electronics / beginners

author: K3mHtH
author_rank: Regular Contributor
timestamp: December 31, 2019, 07:51:51 pm
content: Hey everyone,I'm working on a schematic where I have an audio signal coming out of an opamp on one PCB that needs to go into an opamp on another PCB. I'm just wondering where is best to make the "break" connection between these two circuits to do it properly.The audio coming out of the first opamp is 5Vpp. Please see schematic..

author: rstofer
author_rank: Super Contributor
timestamp: December 31, 2019, 10:26:31 pm
content: I like the first scheme because I would want the signal coming off a board to be as high as possible in terms of voltage and as low as possible in terms of impedance.

author: alanambrose
author_rank: Frequent Contributor
timestamp: January 01, 2020, 02:59:41 pm
content: Yeah, agree - maybe an SMA patch lead?

author: Mr Evil
author_rank: Regular Contributor
timestamp: January 01, 2020, 11:20:50 pm
content: To provide a contrary opinion, Break 2 will be more resilient in the case of a fault. R4 will pull the input of U2A to ground if the connector comes loose, and R3 will limit the current from U1A if the connector is shorted (though TL074 has output short circuit protection, so it would probably survive regardless).

author: David Hess
author_rank: Super Contributor
timestamp: January 01, 2020, 11:41:23 pm
content: I agree with rstofer; the high signal level with attenuation at the input means that common mode noise (ground noise) is attenuated as well. Note that you may need a low value series resistor at the source to allow the operational amplifier to drive the line without a local oscillation.But if ground noise is a problem, then there are two simple and cheap ways to solve it:1. Use two wires with one being the signal ground, actually common, from the source and then use an instrumentation amplifier at the receiver. Usually a simple 4 resistor difference amplifier provides sufficient noise rejection.2. Send the signal as a current instead. Make the transmitter operational amplifier into a current source, sink, or pump, and provide a resistive load to ground (common) at the destination followed by a buffer.I have used both methods very successfully when transferring audio signals even between separate chassis.
Opamp gain control - Page 1
Forum section: electronics / beginners

author: dfox416
author_rank: Contributor
timestamp: November 12, 2013, 05:18:24 pm
content: What are the advantages/disadvantages/differences between using a pot as the feedback resistor for an opamp to change the gain and using a pot after the output to attenuate the signal?

author: tszaboo
author_rank: Super Contributor
timestamp: November 12, 2013, 06:27:58 pm
content: http://www.maximintegrated.com/app-notes/index.mvp/id/1828anything particular?

author: Jon86
author_rank: Frequent Contributor
timestamp: November 12, 2013, 09:22:59 pm
content: Well you've got to remember that a potential divider's output voltage is dependent on load current. If you use a pot on the output of your opamp you'll end up with an output that isn't stable if you've got anything loading it. Put the pot into the feedback loop, and the opamp will obviously correct any error on the output. Whichever way you do it, you'll have noise generated, but the feedback resistor is more common.Also, if you have the pot in the feedback, you can change the gain ranges from 1 to huge, while keeping the low ranges clean. If you're always using a high gain and just attenuating it afterwards, you're going to create a load of unnecessary noise.
OpAmp Help - Page 1
Forum section: electronics / beginners

author: Dazzer
author_rank: Newbie
timestamp: July 24, 2022, 12:37:05 pm
content: Hi Guys,I'm chasing my tail trying to modify a circuit that I currently use for different voltages. It basically takes a 0-3.3v input, and converts it to either 0-10v, or -5 to +5 depending on a switch position.I would like to change the input range from 0-3.3v to 0-4v, and switch the unipolar/bipolar option using a RP2040 GPIO pin (3.3v), but I can't seem to do it without adding a second opamp and quite a few extra resistors.Can anyone suggest a single opamp circuit to achieve my goal?Cheers,Daz

author: Kleinstein
author_rank: Super Contributor
timestamp: July 24, 2022, 01:09:53 pm
content: The IO pins do about the same as the switch to the left: either connect to GND or the positive supply (3.3. V).To change the range, one can adjust the 100 K resistor in the OP-amp feedback: more resistance for a larger range and less for a smaller range. To get 0-4 V or +-2 V it would be some 10.6 K in the feedback.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 24, 2022, 02:13:17 pm
content: Are you sure your uC can switch an output pin to 5V? 5V tolerant inputs do not mean they can output 5V, and I think that 2040 thing only has a 3V3 power supply.For range switching, you can experiment with a resistor going to an I/O pin, and then switch that pin to an input (preferably analog in, or some explicid high impedance mode)

author: Dazzer
author_rank: Newbie
timestamp: July 24, 2022, 03:41:18 pm
content: Thanks guys.Maybe a video would help? I think my lack of knowledge makes it difficult for me to explain the question adequately.Simply put, I need to ditch the mechanical switch, and attach it to a RP2040 pin (the dotted box). Then change the gain to cater for change from 3.3v to 4v input range.If it helps to know the application, the 3v3 was filtered PWM, and now I've moved to a DAC that outputs 4.096v. So basically, I need to convert a swing of 0-4v to -5/+5v, or 0-10v switchable by the uC.

author: jwet
author_rank: Frequent Contributor
timestamp: July 24, 2022, 03:56:19 pm
content: Try this- it uses minimal components and gets pretty close. If you need more accuracy, you need to add an op-amp.

author: Dazzer
author_rank: Newbie
timestamp: July 24, 2022, 04:14:48 pm
content: Hey jwet,That's good enough for meI'm 4 months into studying electronics, and theory and practice still seem like different worlds to me at the moment.Cheers!!

author: jwet
author_rank: Frequent Contributor
timestamp: July 24, 2022, 04:27:13 pm
content: Glad to help.The problem in keeping it very simple is that the gain required to go from 4 to 10 is 2.5. This would give a negative gain when you input the offset of 1.5 (gain of inverting is just rf/rin vs rf/rfin +1). 5/3.3 is the gain required to give you the offset- is 1.515. So you can't quite get there. I tweaked the positive gain a little to make it work- it gives a little extra at the ends but is a good comprimise. You could do it exactly with one op-amp and more resistors but this is probably good enough I thought.Have fun.
OpAmp input noise and noise gain - Page 1
Forum section: electronics / beginners

author: raff5184
author_rank: Regular Contributor
timestamp: April 25, 2018, 04:20:13 pm
content: Hi all,few questions about op amp input noise and noise gain.1) Given the input noise voltagen(typically in [nV/sqrt(Hz)] ) if I want to know the noise voltage in output, I calculate:n*sqrt(Bw)*AwhereBwis my bandwidth andAthe closed loop gain.But what if I work only at one specific frequencyf*? Is it simplyn*A?2) Ifnis not constant but changes with the frequency (for example seeFigure 11:https://www.apexanalog.com/resources/products/pa90u.pdf), and I work in the range, say from 10 Hz to 1kHz then I need tointegratethe input Noise Voltage curve given in the datasheet over the operating frequency range, correct?3) The noise gain.The AD Tutorial (page 3:http://www.analog.com/media/en/training-seminars/tutorials/MT-033.pdf) says that: "Noise gain is equal to the signal gain of a non-inverting amp. Noise gain is also the same for either an inverting or non-inverting stage.".So, in case I am designing aninvertingop amp, by which gain do I need to multiply the noise? Non-inverting gain?Thank you

author: awallin
author_rank: Frequent Contributor
timestamp: April 25, 2018, 06:13:37 pm
content: Try this video series by Analog Devices:https://www.youtube.com/playlist?list=PLBD1F10D92010F8D7

author: Marco
author_rank: Super Contributor
timestamp: April 25, 2018, 06:40:18 pm
content: Quote from: raff5184 on April 25, 2018, 04:20:13 pmAt one specific frequency the noise is zero, it just takes longer than the universe exists to measure it. Or in other words, there is no such thing as one specific frequency outside of mathematics.

author: David Hess
author_rank: Super Contributor
timestamp: April 25, 2018, 10:24:35 pm
content: Quote from: raff5184 on April 25, 2018, 04:20:13 pmYes, at one frequency, the output spot noise is just the input spot noise times the noise gain.QuoteThat is correct. You can integrate either the input noise and multiply by the noise gain or integrate the output noise to get the same result.QuoteEquations 2, 3, and 4 on page 3 of MT-033 cover this. For a non-inverting amplifier, the closed loop gain and noise gain are the same. For an inverting amplifier, the noise gain is 1 plus the signal gain. I usually ignore this difference but it can matter at low inverting gains.
Opamp or Transformer for Balanced Car Stereo Hack - Page 1
Forum section: electronics / beginners

author: sonicj
author_rank: Frequent Contributor
timestamp: March 22, 2012, 11:38:59 am
content: I hacked up the balanced line outputs on the cassette deck in a '07 Toyota Avalon to provide a stereo line input from a external source (ie: phone, ipod, etc). The hack works as I had hoped except the signal from a typical portable device is apparently much lower than that of the original tape deck. Should I:A. Use a pair of 1:2 Audio Transformers to step up the voltage between the source and the amplifier?B. Use a Opamp to step up the voltage between the source and the amplifier?The stock cassette used balanced outputs in case that matters...Thanx!-sj

author: T4P
author_rank: Super Contributor
timestamp: March 22, 2012, 12:54:39 pm
content: Use a opamp preamp .http://tangentsoft.net/audio/cmoy-tutorial/You can use any opamp you want , no need to listen to them .

author: sonicj
author_rank: Frequent Contributor
timestamp: March 23, 2012, 09:01:33 pm
content: yes.But why Dave.S? Why should I use a Chow Mein headphone amplifier to match the unbalanced signal from a portable media player to the differential inputs on the Toyota head unit? Why the opamps over a simple passive transformer solution Dave.S? WHYYY?-sj

author: T4P
author_rank: Super Contributor
timestamp: March 24, 2012, 06:13:46 am
content: Quote from: sonicj on March 23, 2012, 09:01:33 pmLosses . Frequency roll off of the transformer and lastly , cost .
Opamp Oscillations and 1N4148 for clamping - Page 1
Forum section: electronics / beginners

author: AQUAMAN
author_rank: Regular Contributor
timestamp: April 03, 2014, 08:20:07 pm
content: I am measuring the gate voltage of a MOSFET/IGBT with respect to temperature. The MOSFET has a gate capacitance of around 80nF.I am only interested in the first part of the gate voltage waveform (where the voltage settles just after the overshoot due to the inductance).To do this I have used 2 opamps, a follower and then an opamp to sense the difference between the gate voltage and 2.5V reference.As I am only interested in the first section the gate voltage waveform, and I know that roughly this will be around 2.5V, I have clamped the voltage with 2 diodes as you can see to around 2.5V (+- the diode voltage drop). Then at the end I then compare the voltage to a 2.5V reference and feed into an ADCMy first question is on the clamp. In the simulation here I have used MMSD4148 diodes and it currently works. However, in the LTSpice model this has the junction capacitance at 0.64pF. When I change this diode to a standard 1N4148 diode (4pF capacitance), the clamp no longer works and it seems that the diodes are too slow to cope. However, I'm not sure I trust this simulation - the lowest capacitance I can find for these type of diodes in a surface mounted version is around 1.5pF, not 0.64pF. I would like to know whether its realistic that these diodes in the real world will be able to work with this fast moving voltage like gate voltage. I have put a little low pass filter before the clamp but I can't attenuate the high frequencies too much as it destroys the variation I want to see.My second question is controlling the oscillations in the op-amp. You can see in the voltage follower output thse small oscillations and to some extent in the voltage for the ADC input, which I assume will get worse when I build it in real life. I can control them by changing to a different opamp, but at the moment I am stuck with LT1363. What can I do to remove these oscillations?Any help is much appreciated, hope I explained everything well

author: AQUAMAN
author_rank: Regular Contributor
timestamp: April 03, 2014, 09:41:25 pm
content: Actually ignore the diode question - I am fairly sure after more simulation that it will work
OpAmp Rail Voltage Margin - Page 1
Forum section: electronics / beginners

author: beaker353
author_rank: Unknown
timestamp: March 15, 2014, 04:24:56 pm
content: I have a project that I am working on that will use an opamp to buffer a DC signal to a number of adjustable power regulators. The opamp circuit will be arranged as a voltage follower with with the power supply rails across a pot, pot wiper tied to the opamp input. I know that most (if not all) opamps are not able to drive the full voltage of their power supply rails. From my understanding, even rail-to-rail opamps have some margin. I don't think I have a need for a rail-to-rail opamp, but I am having a hard time determining from the datasheet how much margin is required to stay in spec on parts I'm considering. Do I just not know the name spec I am looking for? Do I need to derive this number from more than one datasheet spec? Thanks!-EM

author: kg4arn
author_rank: Unknown
timestamp: March 15, 2014, 07:05:45 pm
content: Take a look at the LM741 data sheethttp://www.ti.com/lit/ds/symlink/lm741.pdfI am not suggesting this op amp, just an example.Look at the spec called "Output Voltage Swing." It tells you that the LM741 has a minimum output swing of +/-12Vwith a +/-15V supply and a 10K load. You have to extrapolate ( and test) for supply and load conditions that are not specified.Another consideration is the common mode input voltage. If you are using a non-inverting configuration like a follower. On this data sheet it is the "Input Voltage Range" spec and it is specified for supply voltage of +/-15V. The minimum for the LM741 (not the A or C versions) is +/-12V. So if either of the inputs gets outside this range, the op amp behavior is not specified. Might work, might not. Might work for one unit and not another. So you have to keep the input voltage on the + pin of your follower inside this voltage range.

author: w2aew
author_rank: Super Contributor
timestamp: March 15, 2014, 08:18:59 pm
content: Quote from: beaker353 on March 15, 2014, 04:24:56 pmMost data sheets will include some graphs that indicate the output saturation or output voltage swing capability vs. load current. From this, you should be able to see if a particular device will meet your drive requirement.
Opamp surrounded by transistors circuit?  - Page 1
Forum section: electronics / beginners

author: maps
author_rank: Newbie
timestamp: May 06, 2019, 07:46:02 pm
content: Hey guys,I have an old used dbx 166a compressor which has a few problems that I am trying to solve. I am quite new to electronics so using this cheap repair as a learning experience.The issue I am looking at currently deals with the circuit I included, the pot (gate thres) seems to almost be getting VAC (no scope here so not 100% on this) during the first 1/4 turn left before it switchesto a normal value (on the 'working' channel I get -1.6 for the pot fully left, and about -1.8 at max value never but never a + voltage and certainly not a fluctuating one).I am measuring this on the listed TP in the circuit, which brings me to the topic question...What exactly is this circuit supposed to do? I have a rough understanding of opamps and transistors but the layout is above my level so any help deciphering it would be appreciated.I assume it is some know layout with a name so even pointing me in that direction would be great.Additionally, any thoughts on what could be causing the voltage fluctuations would be a bonus.

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2019, 08:57:22 pm
content: Several of those transistors are used as diodes, and it looks like they used a 0 ohm resistor as a test point, likely it was easier for the assembly machine to load a resistor there than a loop of wire. With that in mind it may be a bit easier to follow.

author: maps
author_rank: Newbie
timestamp: May 07, 2019, 09:29:04 pm
content: Ok using them as diodes is something I had not considered, thanks

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 08, 2019, 03:03:16 am
content: Would have to take a closer look at it, but using diode-strapped transistors, especially monolithic arrays (matched transistors, thermally coupled), sounds like a log amp, or a function related to that (like a squarer).Tim
Opamp won't agree with me + everycircuit !  - Page 1
Forum section: electronics / beginners

author: Odd
author_rank: Regular Contributor
timestamp: January 21, 2020, 08:47:06 pm
content: Please see schematic tested in EveryCircuit:The positive-side current sensing works, both inputs are pretty high, the amplification of 66.6 times works, and the output is 2.54v, well within the 15.3v that the opamp is hooked up to.Now the reality:LM324 is connected to full battery voltage.Built, as in the drawing, the opamp's inputs in respect to it's GND are:when idle:+input is 224mV (in respect to opamp's VPP)-input is 214mV (in respect to opamp's VPP)so input is only 20mv from VPP, and the difference is only 20mVthe output is about 78mV (relative to ground)(All good, I do not need a very precise measurement.)with 10 A load:+input is 224mV (in respect to opamp's VPP)-input is 235mV (in respect to opamp's VPP)so input is only 21mV "in the other direction", and the difference is only 20mVthe output is about 78mV (relative to ground)What do I do wrong ? - Too close to VPP ? - I've used the same opamp on the low side, having the -input pulled almost to the ground, and +input 1v above, and the difference works fine then..

author: Vovk_Z
author_rank: Super Contributor
timestamp: January 21, 2020, 08:58:29 pm
content: I don't know about simulation model (it depends) but real LM324 (LM358 etc) work with signal near ground, but not near positive supply rail.

author: magic
author_rank: Super Contributor
timestamp: January 21, 2020, 09:35:58 pm
content: Indeed, if both inputs are within 1V of VCC the input stage of LM358 turns off and stops controlling the output. The output goes down regardless of what's happening to the inputs, until they leave that region.Try TL072 instead, it's the other way around: works close to VCC, doesn't work at ground.Beware that many TL072 from auction sites are fakes, often relabeled LM358

author: Odd
author_rank: Regular Contributor
timestamp: January 21, 2020, 09:52:58 pm
content: Thank you all.Yes, the "some will work high, some low" makes kind of sense with other circuits I've seen.
opamps & can theremin - Page 1
Forum section: electronics / beginners

author: Jegeva
author_rank: Newbie
timestamp: June 03, 2014, 10:27:45 pm
content: Hello Guys & Gals,i'm fairly new to electronics, as a lot of people Dave enthusiasm took part in reactivating the old nostalgia i had lingering from my school days about breadboard and resistors.Saw this :http://www.instructables.com/id/Theremin-Using-a-Soda-Can-and-the-Digilent-Analog-/?ALLSTEPSon hack a day and said to myself let's give it a try !.But i don't even understand the operation of the 1st building block, rewatched dave's post on basic op amp operation and can't figure out why the first block :should produce anything on the output, + & - inputs are at the same potential and hence the op amp, doing it's best too keep them at the same potential...have nothing to do ! Both are at ground potential already...I'm surely missing something, can you please shed a bit of light for me on the matter ?

author: Andy Watson
author_rank: Super Contributor
timestamp: June 03, 2014, 11:03:01 pm
content: Put, conceptually, 1mV on the positive input and consider what happens next.

author: Paul Price
author_rank: Super Contributor
timestamp: June 04, 2014, 07:59:53 am
content: There is, kinda, put in a 100k resistor from the + input to +5 and squeals and whistles and moans will b urs 2 hear.With the resistor you'll always hear a tone, without the resistor you will always get it to work with some type of squeeze and make crappy sounds, and for free, mains power line hum modulated noises, like in the video linked.Keep things simple, simply is not the ideal case here..crap circuit is tooooooo simple.If you use an input to a CD4001 connected to a 8-in antenna or wire or a metal plate approx the same length and take the output of that same 4001 gate and feed it into the input of VCO you will have a real theremin that you can change sounds from over a very wide range and distance from the antenna.You can make a good VCO from an op-amp or two as well, see attachedHint CD4046 is a good VCO, but forget about the PLL, just the VCO section of this chip.

author: LvW
author_rank: Frequent Contributor
timestamp: June 04, 2014, 08:19:41 am
content: Here is another way to see what the circuit does (and how):Immediately after both voltage supplies are switched on (neverexactlyat the same time) no opamp based amplifier has reached it´s desired "starting position" at t=0. Hence, assume the opamp will start with Vout=+V(supply) or -V(supply). Then, calculate both of the input voltages - taking into account the charging process of the capacitor - and see what happens.

author: Jegeva
author_rank: Newbie
timestamp: June 04, 2014, 04:12:53 pm
content: Quote from: Paul Price on June 04, 2014, 07:59:53 amCompletely made it work(on the breadboard, the original setup output was keeping flat at 1.smthng V on the oscillo)Quote from: LvW on June 04, 2014, 08:19:41 ami don't have time for this tonight but i'll definitely give a shot a this method tomorowthanks guys
Opamps for everyone PDF - Page 1
Forum section: electronics / beginners

author: Inverted18650
author_rank: Frequent Contributor
timestamp: August 06, 2017, 05:02:33 am
content: I was browsing other posts and found a link (OP rstofer). Everyone should save a copy.https://focus.ti.com/lit/an/slod006b/slod006b.pdf

author: bjcuizon
author_rank: Frequent Contributor
timestamp: August 06, 2017, 05:54:50 am
content: Thanks for posting!I had a read through it and it seems really informative. Maybe i'll read it during some of my free time (it's quite long though). I'm sure analog guys like me will like it.

author: danadak
author_rank: Super Contributor
timestamp: August 07, 2017, 10:23:03 am
content: QuoteI must be blind, do not see the free link ?Regards, Dana.

author: alm
author_rank: Super Contributor
timestamp: August 07, 2017, 10:45:35 am
content: I did not see a link on the store page either, but this link appears to work:https://www.ti.com/seclit/sl/slyw038b/slyw038b.pdf

author: Inverted18650
author_rank: Frequent Contributor
timestamp: August 08, 2017, 08:32:04 pm
content: Quote from: alm on August 07, 2017, 10:45:35 amThanks, handy indeed!

author: rbrucecarter
author_rank: Newbie
timestamp: April 23, 2019, 05:03:51 pm
content: NEW LINK (TI de-activated the old one):http://web.mit.edu/6.101/www/reference/op_amps_everyone.pdf

author: rstofer
author_rank: Super Contributor
timestamp: April 23, 2019, 07:00:33 pm
content: When perusing "Op Amps For Everyone", pay attention to Chapter 4 where the author tells us how to offset and scale signals for use with uCs. Want to deal with battery voltage of 10.5 - 14V, don't want to give up resolution for the first 10.5V, and then rescale to use the maximum ADC swing? Chapter 4 shows how to do it with 4 resistors and a single supply op amp.My favorite chapter!
OpAmps for Solar charge / battery use power monitor - Page 1
Forum section: electronics / beginners

author: cg6
author_rank: Newbie
timestamp: December 01, 2014, 03:25:58 pm
content: Hi All,This is my first foray into analogue circuits so I would appreciate somebody commenting on my plan.I'm building a power monitor for my solar + battery camping kit. I would like to monitor current from the solar panel to the battery, current from the battery to load and voltage at the battery.Analogue data capture will be via a PIC with 5V VDD as the voltage reference. The LP2950 has tight enough tolerances for my needs. I'll calibrate results in the digital realm.I've selected the LM324 op-amp because it is designed for single supply and is linear down to 0V. I'm expecting close to a 25:1 gain on the voltage across the shunts.Thanks,Chris

author: Seekonk
author_rank: Super Contributor
timestamp: December 01, 2014, 03:59:03 pm
content: Solar panel note says it includes charger. That will likely be PWM and will be a full current no current signal. As it is you will get next to useless information on current from panel as it currently is. Add a 1K resistor in series with a 100uf capacitor to form an averaging filter. The resistor values for the voltage amplifier will have to be at least ten times greater than they are now so it doesn't place a load on the averaging circuit.

author: cg6
author_rank: Newbie
timestamp: December 01, 2014, 04:27:56 pm
content: Thanks for the PWM tip.So the RC will be across the shunt and I'll measure between the resistor and capacitor?Also the op amp comes in a quad package so I can setup a voltage follower to reduce load - or is it recommended to use higher resistor values anyway?

author: Seekonk
author_rank: Super Contributor
timestamp: December 01, 2014, 04:55:59 pm
content: A buffer will just add noise and drift. Shame to have that micro and not include a power point charger.
Opamps protected against output short circuit to ground? - Page 1
Forum section: electronics / beginners

author: ocset
author_rank: Super Contributor
timestamp: December 13, 2017, 05:35:05 pm
content: Is it true that all opamps, eg the MCP6001U, are deisgned to withstand their output being indefinitely short circuited to ground?MCP6001U opamp datasheet.http://ww1.microchip.com/downloads/en/DeviceDoc/21733h.pdf..it just seems so very conscientious of the semiconductor fraternity to do this ‘charitable’ thing.I mean suppose one puts 5V into the noninverting input of the MCP6001U opamp when its connected as a unity gain buffer on 5V single supply. The output is short circuit protected against any damage.

author: dmills
author_rank: Super Contributor
timestamp: December 13, 2017, 06:18:54 pm
content: Some of the big power opamps have SOA limits, but most of the jellybean stuff is pretty close to short circuit proof, you do sometimes have rather nasty differential input voltage limits and sometimes get weird things if you exceed those limits.If you are doing analogue on silicon it costs only an extra small transistor or two and a couple of extra resistors to limit the output current, so it costs basically nothing.One other thing to watch is that some parts have funny latchup states if power sequencing is wrong, the NE5532 springs to mind for some reason.Regards, Dan.

author: Audioguru
author_rank: Super Contributor
timestamp: December 13, 2017, 07:59:21 pm
content: ALL opamps are different so simply read their datasheets.The MCP6001U opamp is a low power one with a fairly low maximum allowed supply voltage and a fairly low output current. Therefore at 5V its output current is only about 21mA which when shorted produces only 0.105W of heat.An ordinary opamp with a 30V supply and 40mA max output current would heat with 1.2W and probably smoke and burn.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 13, 2017, 08:38:48 pm
content: There are most definitely op-amps without controlled limits.Most general purpose amps do have controlled limits, or they aren't controlled as such, but the worst-case current is still low enough to survive a continuous short, under normal conditions (op-amp mounted to FR-4 board, in still air, etc.).There are most definitely op-amps without thermal limits. I can't think of one offhand that has a thermal limit. A general purpose amp might be okay into a short circuit for some time, but not under all conditions: high ambient temperature, poor thermal conductivity, unusual circumstances (e.g., mounted on a Teflon board in a vacuum chamber -- basically no thermal conductivity). Rely on that property too much, and you'll screw yourself sooner or later.Op-amps are not power supply regulators. For that, there are regulators, proper! Regulators almost always have a thermal limit (and whether they have a controlled or gross current limit depends on the design, usually HDO is good vs. LDO sucks).Tim
open bench logic sniffer does not working - Page 1
Forum section: electronics / beginners

author: mrjoda
author_rank: Regular Contributor
timestamp: November 12, 2016, 02:21:08 pm
content: Hi guys,i bought OLShttp://dangerousprototypes.com/docs/Open_Bench_Logic_Sniffer. I tought it will be without complications but... aaaaaaaaaagh...after few hours of trying i finally flashed new firmware, problem with switching to bootloader mode all time. Now its have a new FPGA rom and PIC FW.Device is installed properly, after connection to PC i see OLS in device manager with no problem, but is it impossible to connect it with some software. Sigrok PulseView cant find it, Jawis OSL too. It works 5 minutes maybe and now it is lost completely. I am using windows 7, several times i tried uninstal device and reinstal drivers but without success.please do not write solutions as "reinstal driver" - i tried, "reinstall windows" - lol nope, "try linux" - nope, and so... i am not newbie i tried lot of things but without successcan you help me ? Dangerousprototypes is almost dead so i hou you can help me with this piece of sh&#t...i have same problem as this dudethanks a lot
open circuit reading of multimeter in mV range - Page 1
Forum section: electronics / beginners

author: d3javu
author_rank: Regular Contributor
timestamp: October 12, 2010, 10:24:58 am
content: Hi folks,I have just bought a Uni-T UT61C multimeter and while playing with it, i notice that the voltage reading in mV range is increasing constantly and sometime when i turn on the multimeter and straight away set it to mV range, it shows overload. Previously, i have been using cheap multimeter which never had such a behaviour in 200mV range.

author: scrat
author_rank: Frequent Contributor
timestamp: October 12, 2010, 10:54:24 am
content: Couldn't it be that it catches some noise? They have a very high input impedance, and signal is rectified for DC measurement, so I suppose noise rectified charges input capacitance and makes voltage grow up.Have you tried to go, for example, outdoors? Does the problem increase if you touch a terminal?

author: d3javu
author_rank: Regular Contributor
timestamp: October 12, 2010, 11:09:47 am
content: here is an example, another thing is while on auto range, after 60mV, the value jumped to 200+, obviously the range changed automatically but the value jumps from 60mV to 200mV is kinda weird to me. the probe is not in contact with anything. there is only a fan running next to me, i did move out and try, it is the same. it is normal??

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: October 12, 2010, 11:26:53 am
content: As long ,when you sorting the leads , the reading becomes 0000 your multimeter is healthy.

author: d3javu
author_rank: Regular Contributor
timestamp: October 12, 2010, 12:24:01 pm
content: Nah, i'm just curious about the reason behind this behaviour. The voltage actually decreases after it reaches about 200-250mV at very very slow rate.

author: saturation
author_rank: Super Contributor
timestamp: October 12, 2010, 03:08:20 pm
content: Sensitive DMM will pick up every stray EMF out there. To eliminate it, remove the impedance between the probes tips so there is no potential difference between them, this is done by shorting it, as you did, it then stops.If you had an oscilloscope, you can actually see the waveform of the EMF, usually it picks up line voltage radiation at 60 Hz, in the USA.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 12, 2010, 03:26:08 pm
content: short the leads, some caps charging up and down in there. you know... very sensitive to "the power of the force"

author: Time
author_rank: Frequent Contributor
timestamp: October 12, 2010, 04:46:22 pm
content: Its just your leads detecting basic background radiation or EMI. Things of this nature are very stochastic and difficult to pinpoint but its probably from your mains or something.

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: October 12, 2010, 06:04:00 pm
content: QuoteYou win the Proper Use of Uncommon Vocabulary Award for this week!!!!

author: Time
author_rank: Frequent Contributor
timestamp: October 12, 2010, 06:39:24 pm
content: Quote from: JohnS_AZ on October 12, 2010, 06:04:00 pmHaha, sweet!