How to use op amps with a single rail power supply
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- เผยแพร่เมื่อ 20 มิ.ย. 2024
- Operational amplifiers are commonly used with a dual rail power supply, but it is possible to use them with a single supply. Watch to see how it is done and to avoid the pitfalls in doing so.
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Such a lot of detail and very easy to understand, thank you, very informative.
Thank you for your detailed explanations and greetings from a German subscriber
You are the best teacher i ve ever had. Thank you so much for everything.
John, Excellent Video!!!
My mind was blown, not only did I not know there was such thing as negative voltage, but as well as a relative ground? I’m so surprised. Thx and nice vid! 👍
i was just waiting for a video like this!! thanks from italy
I learned a lot here - Thank you
Very well explained. Thank you
Great tutorial. Thanks!
nicely explained. Thanks.
Well explained..thank you so much. Just like LMC7660 charge pumps
This video did the trick! Thanks
Thank you for the informative vid John! So, in this vid, in the 3rd case, you showed how to bias the non-inverting, a.c. amplifier configuration. But how do you bias a subtractor (differential) a.c. amplifier configuration (two a.c. inputs simultaneously - one on the non-inverting input and the other on the inverting input of a single op-amp)???
thank you ! nice video.
John, Thank you for that Explanation of Virtual Ground. I have a good grasp of resistor voltage dividers but I really struggled to understand virtual ground until I saw that simple passive voltage divider with your explanation. I've looked through a lot of videos, most focus only on op amp virtual ground but they are vague. With the resistors and nodes, it's simpler to see a virtual ground.
Thank you
-Christopher
Thanks Christopher! If I can help a few people out with my videos, I have met my goal.
John, what are the advantages/disadvantages of the 3rd option? Is it generally preferable?
Thanks heaps, Cheers :)
There is also another possibility, if you don't like to lose your ground reference point: a dc voltage inverter. This is especially useful in medium power applications like amplifiers. I have allready used a boost converter as "voltage inverter". In this case the ground is the positive potential of the input voltage. The converter generates the new positive potential.
In general, in step up/down converters, the ground of input and output are connected together, so you're actually short-circuiting you power supply, how did it even work for you? 🤔
@@alessioulivi6734 If you use a boost converter the + Input becoms GND output, the - input is - output and the + output is generated by the boost converter.
great stuff
If you had two power supplies, they wouldn't necessarily have to be isolated, you could tie the virtual ground to the ground of the other supply so that they have a common ground reference, right?
consider me subscribed... Good video. I have some circuits that need positive, negative, and ground. This explains how, and might work for what I am doing.
Would you have to also choose resistor values that are low enough to supply enough current? Seems bad that the divider network will constantly drain the battery at a high rate. What about just setting noninverting input to half supply voltage? Then you still need to use coupling caps yes but you still have a common ground. Just make the opamp settle on half output voltage by biasing on of its inputs to half supply. ..
i will try this with the 4558d ic for the tda2030a to make a subwoofer amp. but i can't really find any datasheet for those
Hi John. Another interesting video here. I'm building a guitar amplifier for fun and to learn something new. The pre-amp and power amp are running from the same supply, the pre-amp works with a single supply and the power amp runs from a dual supply by a passive voltage divider (as shown in the video). Obviously if I connect the audio signal from the pre-amp to the power amp the audio ground will suddenly be referenced to the negative rail (also creating a short between the negative rail and the virtual ground). How would be best to deal with the virtual ground isolation? Would I use a 1:1 audio transformer or would I just have to add a coupling capacitor to the audio signal between the devices and a coupling capacitor to the audio ground between devices? Jim
When on the same supply, why not run the preamp dual as well? If high voltage is the issue, you can regulate it down for the pre. Why did you decide to use the virtual ground split supply on the power amp?
I'll have a go and alter the schematic to see how the pre-amp runs on the dual supply at lower voltage. I went for the virtual ground split supply on the power amp as I'm using an LM1875T board (the same one that you use in some of your videos) and am attempting to work on a tight budget so decided to use a 31v 4A power brick I already had. I wonder if running the power amp from one power brick and the rest of the circuit from another power brick (double insulated, so no earth) would be a simpler solution.
Input 12v output 6v makes so much sence
I'm confused by the second example. I know this video was posted a few years ago, but I would really appreciate some clarification if anyone can explain.
I want to make a supply rail splitter so I can power an op amp. If I don't have a negative rail yet, what do I connect to the op amp power in the second rail splitter circuit? I feel like if I knew the answer to that, maybe I wouldn't need to make this supply rail splitter at all?
What are the voltage and current requirements needed from the supply? For example if you you needed +6v and a -6v rail, you would power the example circuits with 12v.
@@JohnAudioTech I need 12 and -12. So I can connect 0 and 24 to the op amp?
If so, since what I'm ultimately trying to do is power an op-amp oscillator circuit, does that mean I can forego creating a negative rail and just use 0 and 24V for that as long as the difference is the same?
watch this video to find out how to use an opamp to provide the power for the opamp you need. it's like a damn snake eating its own tail, a recursive hell specially prepared by monsewer here.
i love the very first comment, "now how do you power the opamp in the active circuit"
i wish i'd read it before i watched it. at least our masonic pal let slip the phrase "active rail splitter" but i can see, i'm really going to have to wait until the parts get here and do it myself to learn instead of watch videos.
it's nice ot see the precise 3.66 voltage and perhaps from other references, the appropriate use of capacitors can be discerned, but it would of been teh flimming nice if you boy had just put one fricking circuit for reference so teh lowly can not have to take it teh rough boy One More Time.
thanks J :-)
does it affect its performance?
This is a very important video. But what if we need to virtual ground more opamps? can we use the same bias or it will make a full short circuit to the signal?
I wouldn't use any of these methods on complex circuits. That 10mv riding on the virtual ground would get multiplied by the gain of the second amplifier and multiplied by the gain of the 3rd amplifier and so on.
Bom bem explicado.....
I've been struggling with this for a VERY LONG time:
How does one find/build a decent split power supply without spending a fortune on transformers? The virtual ground circuit you showed only works for pretty low power applications according to my research. I'd like to go as high as around 50 watts per speaker (hard to specify a limit at this time, because I haven't fully tested these speakers yet).
You could go the simplest way and use two DC power supplies in series, and taking the middle point as your ground. That's what I'm going to do for a few projects I'm working on. How much current does your circuit handle?
What is the value of the biasing resistor in example 3?
ehhh.... maybe a stupid question but how to power the op-amp used to build a symmetrical powersource that is needed to power up op-amps???
Yeah I'm interested too xD At 10:07 he says something
Kinda late, but you just use the negative and positive voltage of the voltage source (in this case the battery) to power the opamp. Remember it's all about having a middle point to call ground, that's the objective of the circuit. The neg and positive voltages are already there in the battery connectors.
@@ramiro6322 Just to add, although op amps themselves do not require a 0V ground, the reason we are generating a 0V reference for the signal op amp (not the ground-generating op amp) is that op amp amplifier circuit designs need a ground to reference the signal to. The chip doesn't need a 0V but the amplifier as a whole does.
Or you could use a LM317 for single supply and both the LM317 and LM337 for dual supply. The same concept as the third method since the LM317 and LM337 are basically OP-Amps configured as buffers. They have stable output voltages, high current outputs of 1.5 amps each and less component count. But the trade off is energy wasted in the form of heat.
Thanks for sharing this info, I’ll have to try the LM317 as a dual rail power supply for testing my op amp because I am working with a frequency of 300KHz so the passive technique does not work very well at that frequency level.
Can u provide any idea to convert 28 volt 6amps single supply to covert 24-0-24 volt transformer is toradial
Hey great video very instructional! I am wondering about the Active circuit's opamp. Are you powering the op amp with the voltages from the battery? Is this op amp different from the op amp being powered from this circuit?
Thank you!
Hi,
I tried this passive circuit, not with 9v battery, but with 12 x aa batteries.
I tried this to get power to the LM1875 board, you know your vid "LM1875 IC audio amplifier board kit test and review"
The + - was balanced about 8.25 +-
The stereo from my phone was converted to mono via male/female jack, and fed into board.
Speaker was a 60w (smallish decktop speaker)
Also the resistors salvaged were small, 1/8 w (1/4 inch in length)
...I got nothing in the way of sound.
what I got was crazy hot battery packs ;) ha...
Was it the amps??
What do you think?
Ta
What are the resistors value? I think you should increase both resistors to 4.7 kohms or more but both the same resistor.
what is connected to the power rails of the opamp in the 2nd active circuit?...if this opamp needs a dual supply..then we are going in circles!!!!
You could theoretically run all of your op-amps biased to run with all positive voltages and then block the DC component at the end via a subtractor or a blocking cap
@Hunter Johnson Hello sir. Please provide full blueprint and assembly instructions. God bless.
I don't understand what's going on in the breadboard at all, why are there power bjt's and what are their purposes. It'll be helpful if someone can explain the schematics for the passive circuit. I'd like to build it on my breadboard as well
What are the capacitors used for? Are they coupling capacitors?
Smoothing out the power and for supplying power quicker in case there are power spikes.
So this is like taking a single supply and using it to produce a dual supply ... and maybe I missed something, but what about where you simply hook your single supply straight to the opamp power inputs?
I've got a project (currently on hold while I work through something else) where I'm trying to build a simple audio mixer that can take input from a CB, phone, and microphone and mix those signals together and output then out to some speakers, back to the CB and phone, and also to a camera.
The application for that would be on a motorbike for vlogging purposes, so the only power available is 12VDC single supply from the battery. Unless I use some kind of DC-DC concreter that can output +- voltages.
You are connecting the single supply to the power pins of the op amp. If you look at the diagrams, you can see they pass on through. It is that virtual ground that the op amp needs for its 0 volt reference to work. And that reference ground needs isolated from other circuits that share the same power supply.
That would give positive and neutral voltage, 0v. Try it for yourself.
How is this different from a simple voltage divider with measuring voltage at lower V end with respect to the center tab of the voltage divider? It would also read negative voltage just the same...
The voltage divider is always drawing current from the battery. You could fix that by making the resistors bigger so they consumme less current, but in that case the big resistors will create voltage dividers with the other components you'll connect to the power supply, lowering the voltage output.
I have a question , now how do you power the opamp in the active circuit
this video ought to come with a warning, "abandon hope all ye who enter here"
but he does say "active rail splitter" at one point
if I take your active dual supply circuit, should I get enough current to drive ,for example 4 OPAMPS, as load???? I actually need a dual supply that will power up some opamps as different filters. Will I get enough current to drive at least 4 OPAMPS???? thanks Sir !
Sayantan Maiti 4 op amp
Hmm calculate additional quiescent current value of all opamp
And now calculate resistance
R= (single supply voltage)/(4*total quiescent current of all opamp)
Resistance calculated will divided in two part
Take lesser than calculated value
Oh man this gets confusing lol but i have to *learn this*..I never learned much about positive and negative outputs to power things...
What worries me is when I put a load on a lm1875 kit will it pull that VG to positive when a ac waves (sound signals) is going in the amp and powering a speaker..
Well i guess ill try it on a breadboard but i dont want blue smoke coming from my kit 😢
I went the ez and lazy way....wonder if you ever used one of these..I will still learn this circuit 😃 m.ebay.com/itm/Single-Supply-to-Dual-Power-Virtual-Ground-Power-Supply-Kit-f-RA1-headphone-AMP/201446796043?NAV=HOME
Buy dual supply it will cost less
Take it from me, themore exposure you have to electronics the more sense they will make. Just keep at it and it will eventually click.
Now, how does one create such 'true dual supply' power supplies? I have searched the net everywhere but can't find a design that's beefy enough to power the LM-Something power amplifier modules that require dual voltage.
You can use a transformer with a center tap, but the price is prohibitive. I have the same problem.
Use a transformer with 2 identical secondary windings connected as a centre tap transformer. The AC phase of each winding must be correctly connected so they don't conflict each other. Torriodial transformers usually have a diagram or colour coded leads. In this case 2 leads would be used on the centre tap. Traditional EI transformers are labelled Vout - 0v or again have colour coded leads - the centre tap lead being a different colour from the other 2 leads, especially on sub- minature types of transformer. A rectifier of at least 8A to 10A rating should do for 2 LM1875 amplifiers assuming a 2 × 3.5 amp output maximum.
The TDA 2030 amplifier ic datasheet has a transistor boosted amplifier option. I don't know how well this would work as a supply splitter with the non-inverting input fed by a 2 × 2.2kΩ to 2 × 4.7kΩ potential divider across the supply rails. The centre of this divider is decoupled with a single 2.2uF capacitor. The inverting input is fed from the output. The output can be decoupled with 2 × 220uF capacitors across the supply rails and output. The booster transistors could do with series limiting resistors to help prevent an across the supply short circuit. A supply splitter circuit with just the TDA 2030 amplifier appears in Power Supply Projects by R.A. Penfold with 100uF capacitors across the output and supply rails. This Babani Publishing book is also useful for sorting out a conventional linear mains transformer supply. Ref.BP 76. ISBN 0 900162 96 1.
Example 1 & 2: Vcc+,GND,Vcc-
Example 3: ????
Story time:
I'm trying to run a motor control that reads 0-5V, but my programmable output has a range of 0.02-4.74V so it's not able to run the motor at full speed. So I'm trying to use a simple non-inverting op amp LM-741 set up with a 12v DC power supply. Well, the splitter works like a charm until i plug in my motor control wire. Turns out it has a 1k ohm resistance and my rails go from +-6V to +2 -10V. So I tried building my splitter with 1k ohm resisters and that helped a little bit. Anything smaller just gets burnt up. I tried using the op-amp set splitter too but that didn't seem to do anything at all....
Could you explain why a resistor from a naked opamp output to the virtual ground shorts the circuit out like that? And what options I have to fix it?
Did you connect the power supply rails -V and +V to the op-amp? Was it powered?
He said it @10:05. Without them, the op-amp does not work.
I think I had this same issue. So what I did was connect the virtual ground to another op amp but that op amp was used a voltage follower (basically high impedance). Then I sent the signal from the voltage follower to the other op amp. This should solve the problem.
So you could actually split it again.
If you use one side of the dual and split it into dual, you could also split it again.
Like you have 24v o 24v you split the one 24v to 12v o 12v use that one side again you will get 6v o 6v???
Yes, but in that case all your resistors have to be the same value. Or you could use just 2 resistors as a voltage divider where the biggest resistor has the biggest voltage.
Is the clamp meter new ?
Yes, it is a $32 ebay cheapy, but it is constructed and works quite well.
I made one and it worked, sort of...
passive.
I found the caps and resistors from a old car tape deck (never used)
caps = 1000 uf (caps had the + and - sides)
resistors = 1k
any way, I soldered it up to a board, the board had no rails of electrical joins, just pin hole type thing (i got 20 from china for next to nothing)
Joining everything together proved to be a bit of a mission-for me anyways.
I was quite happy to see some results at the end haha
*my 9v battery had 8v charge in it.
*the - rail was -3.8v
*the + rail was 4.5v
I soldered the - side of the caps both facing in to the C (VG)... don't really know why, but I did.
Could this be the cause of the un balanced 'unit'?
...I also tested the caps and resistors beforehand and they checked out.
That is a common mistake to face the negative side of the capacitor towards ground on the negative side of a dual supply. The neg side of the cap must face the more negative voltage, so turn the cap on the negative rail so its positive side faces the virtual ground side. Hopefully the light load of the balancing resistors prevented damage.
I changed the cap around and now have a reading
4.22-0-4.27
Now i got to see what I'll power up with this little thing.
Thanks
Use a new cap. When you connect an electrolytic backwards the dielectric breaks down and creates a short. It may seem to work but the capacitance will be significantly affected. Once you connect an electro backwards, it's destroyed. Do yourself a favor and buy a pack on aliexpress. Amazon has them too but they are a ripoff for electronics. Theyre very cheap on aliexpress.
I'm new to these dual rail power supplies. I know I will sound stupid and I'm probably asking for the wrong thing but I need like a 25v dual rail power supply for some of these amps. What do I look for on eBay?
It depends on the load. How much current do they need to be able to deliver at 25 V?
maybe around 3 amps
Then search for one that can offer 3 amps or more @25 V.
9:56 Wouldn't smaller resistors draw more current?
How would you make this for
5 volts?
I need it to power the TL081 op-amps in my power supply kit
Hlo sir how i can 80vdc split to ±40. Please help me sir. I need 40±vdc output
Use the common ground (c) terminal and the +ve of your 80vdc only (ignore the -ve terminal. Then you have a 40vdc. Then you split up the 40vdc into another similar circuit and you have +ve 20v, a common ground (c) and a -ve 20v. thus giving you a 40vdc dual rail supply
@@bq1000bq This sounds all very useful and I am interested, but I have a really hard time following. What common ground terminal are you talking about? A DC PSU is only gonna give you two leads: plus and minus.
@@DasAntiNaziBroetchen
Sorry. My post was for a dual rail supply with a common ground, as in a toroidal transformer.
electro-dan.co.uk/electronics/wiringtrans.aspx
You didn't explain how you power the op amp. This is useless this way