10 Opamps: DC Bias For Single Supply Circuits

[@Gingerbread07]

This is an underrated video

[@deangreenhough3479]

Totally agreed. Beautifully explained thank you

[@gabrielebonotto3087]

I spent days trying to find videos about dc offset for single-supply applications, best video on the subject! thanks for explaining the use of the capacitor to the ground in the not inverting amplifier and the injection resistor! The like is extremely well deserved and necessary.

[@KGrasso89]

I've struggled to understand opamps circuits for months now. Thanks to this video I finally understand how to hook up opamps using a 24vdc wall adapter so I can experiment with active low and high pass filters!

[@realchrisma]

This is a phenomenal video! I looked at various circuits to learn how to work with op amps, but now I know all of the fundamentals in less than 7 minutes!

[@dasgrumpeltier9735]

Maybe on of the best videos on that topic. great.

[@PaulOvery001]

Thank you for, the fantastic video! Understanding this DC Bias has been a real challenge for me, but your explanation cleared up all my doubts. Now, I finally get it!

[@trevortjes]

Hey thank you. This has been the same for me years ago when I started with electronics. I knew I was struggling with this subject in particular and couldn't find any videos or easy explanations on it. That's why this is one of my favourite videos which I just HAD to make eventually so others wouldn't have to struggle.

[@arm-cv7rd]

@@trevortjesNice work, cleared everything up for me!

[@TOmaynardOL]

Great video. I instinctively thought to add a large cap to the power supply, but quickly realized we would filter the input signal as well. Good tip.

[@Jesception]

This is amazing. Very usable for my CV teensy LFO project

[@arenotdiy]

You sir, are a wonderful teacher. Lots of relevant info, good rules of thumb, and I don't need to watch the video ten times to get it. (Although I will so you get the views :)

[@thebeast88_]

Damn am I glad i ran into this video. Everything is explained clearly and properly. I had a bit of trouble finding it again, shame it has only 808 views

[@thebeast88_]

Also, If i have one op amp after the other in a circuit, how do I go about biasing the second one? Seems I can just place a capacitor in between them and bias them both

[@trevortjes]

@@thebeast88_ Depends what topology the 2nd opamp stage uses. If they are two non inverting stages I will take 3:32 as reference: You only have to bias the signal once to +4.5VDC. If you remove Cout, the output will be your amplified signal from the first stage with a +4.5VDC offset. So the biasing is still there! So just directly connect the output of stage 1, to the input to stage 2. This is called DC coupling. Cimportant will make sure that this DC offset will be ignored during the amplification so you need this one too on stage 2.

[@thebeast88_]

@@trevortjes i played around in ltspice a bit and came to pretty much your solution, but i wasnt quite sure so ill just make it tommorow your way. This is a preamp from a guitar amp im making into a pedal so its just one into the other. Thanks for the quick reply man

[@trevortjes]

@@thebeast88_ Yeah good luck and no problem, always here to help!

[@trevortjes]

@@psp_online yes you can lift it by .5v by adding a DC offset. Make sure to use an opamp that goes to gnd like the 358 or 324 because a range of 0-1v is terribly small and cannot be processed by most non rail to rail opamps fed by a single supply. Otherwise use a dual supply on your opamp.

[@MD-qz6gk]

Wooooooow !!!! Man this is the best video on youtube about this argument !!!!!!!!

[@garygranato9164]

thank you for making this video with great diagrams

[@amimaster]

I struggled to find a clear explaination on this subject. Thanks a lot!

[@MrMitdac01]

Thank you alot, those information many people dont want to share, thank again. clear explain

[@jevss9869]

Very informative video. Answer my doubts on single supply configuration (and on voltage-follower). Thank you very much.

[@trevortjes]

0:00 Introduction 0:08 Power Supply Limitations 1:11 Non Inverting Amplifier 3:07 Noise 3:39 Inverting Amplifier 4:21 Buffer 4:42 Component Values 5:45 Recap

[@jonathanj-g-yyelle6144]

Best explanation that I have seen! 👏 Sharing this! 👍

[@SureshKumar-nk2ok]

really iam very thank full to the video presented,it was a long search for this video

[@j3s0n]

Great video, this was very informative. I notice you have other similar videos so I'll check them out in the near future

[@DavitKharshiladze]

One of the better explanations

[@DustinWatts]

Hey Trevor... vandaag je kanaal ondekt (bedankt KZbin aanbevelingen)! Goeie en leerzame video's. Gelijk geabonneerd :) For all English viewers: "Hey Trevor... discovered your YoutTube channel today (Thank you KZbin recommendations)! Good and educational videos. Immediately subscribed :)"

[@adrimilo]

This was a great video, really helpful!

[@fredimachadonet]

Awesome video with great explanation, thank you!

[@elektron2kim666]

This video gave some clues for me on a circuit I'm trying to get further with.

[@pandugofast]

This is so excellent, thank you.

[@MihalisShammas]

Excellent video

[@TheCitygear]

I need this. Thank you!

[@HarshitBujarBaruah]

Excellent video.

[@alexg8233]

Great explanation! Thank you.

[@Parvi_]

Thank You so much for the video, helped me a lot.

[@jayanepal1880]

Just discovered u..u r underrated.thank u..subcribed❤️

[@ferhatkuzu7914]

Thank you for video

[@Uvisir]

just what i was looking for

[@luxi_0oo947]

actual life saver

[@0maxekinge0]

So helpful, thanks!!!

[@Jindraxx20]

Thank you for the explanation !! I have only one question. If you increase the input signal gain , won't you be increasing the DC offset too ??!

[@trevortjes]

If the signal enters the circuit via a capacitor (AC coupled), then the DC offset of the incoming signal can be anything, it won't interfere with the working principle of the circuit. The capacitor only lets anything that alternates through, DC offsets don't alternate. Because it doesn't alternate, it simply doesn't have a frequency. You could happily say that DC has a frequency of 0Hz. Crudely said, capacitors only pass signals higher than 0Hz

[@lezrekmohamed]

Thanks for the educational video. I have made a 3005 lead 12 Marshall preamp. It works well with +17/-17 volts. I tried to make it work with a single power supply using biasing like you showed. It worked with Tl072 but heavily distorted. But didn't work with the original 1458 and JRC4558. What changes should I do to make it work.

[@trevortjes]

Distortion might mean the biasing is still wrong or you are hitting the limits of the opamp. A +17/-17v amp will need single supply power of 2*17=34V. It should work the same for any dual opamp.

[@dar_kkk]

Thanks a lot for the video and the explanation! The information is very important and useful. The high pass filter works great. But it takes time for the capacitor to fully charge, so the first pulses of the signal are distorted. Could you please suggest how it can be "precharged"?

[@marcellusmusic8359]

Thank you for the informative vid trevor! So, in this vid you have shown how to bias the non-inverting, inverting & buffer a.c. amplifier configurations separately. 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)???

[@greendragonmakerspace]

Thanks!

[@pandugofast]

Not expecting an answer here, but I have a question/challenge for you? Why do we not need the injection resistor for the inverting topology? An ideal op-amp will resist a change between it's input terminals, so even in the inverting topology, any ripple on one terminal will mirror on to the other, no?

[@eafindme]

This video is worthwhile to be monetized, and a like.

[@trevortjes]

I've tried to monetize but sadly KZbin keeps telling me my channel isn't up to their required standards. Maybe in the future.

[@ivocapella4541]

Very good!

[@audiokees4045]

Hi There I do test a autobias for a circlotron amp. I want to ask can I use only a negatiove voltage for the opamp rectifier and the low pass integrator opamp? I did try it dit work. Reason is when it go positieve the idle current can get drastic high with a blow fuses as a result, when it can never go positive then the amp start running on idle of 10 mA or what I set as start current with current source. THanks in advance and have happy new year.

[@austinliuigi]

Could you please elaborate on why very high values of the voltage divider resistors would make the circuit susceptible to noise? (4:59)

[@trevortjes]

Two main reasons why high value resistors add noise to a circuit explained as simple as I can: (1) Resistors have an inherent noise due to movement of electrons. This is referred to as thermal noise or Johnson noise. The higher the ohms, the more noise. (2) Electromagnetic fields all around us when coupling with traces, components, wires in your circuits, induce a bit of current. Ohms law: U = I * R Lets make up some nonsense values to better visualize the effects, R = 1 ohm, and the induced current is 1uA. U = 1 * 1uA = 1uV Now lets make this resistance bigger, lets say 100 ohm. U = 100 * 100uA = 100uV. Boom, more noise!

[@lukenonas-hunter5932]

I have a question: for the non-inverting amplifier setup in the beginning of the video, why does the DC offset not get multiplied by the gain of the amplifier?

[@trevortjes]

This is explained at 2:25 using Cimportant. It adds a high pass filter to the system which results in a gain of 1 for DC (0Hz)

[@ivocapella4541]

Excellent!

[@theobject7326]

THANK YOU

[@adespade119]

excellent Video

[@Xambax1]

2:40, why will the DC component make the opamp output slam to the rail?

[@Xambax1]

I answered my own question…if I have a gain of 2, both incoming ac and dc bias will be amplified 2 times. But we don’t want the DC bias to be amplified, we want it to be set in stone by the voltage divider. So adding a capacitor in feedback network will be huge impedance at DC and basically no gain at DC.

[@portblock]

Quick question, the diagram at 3:00, non inverting amp, if this is a buffer/follower, no R1 - output tied to (-) input, no R2, can Cimportant still be used?

[@trevortjes]

With a bit of visual games you can see how that capacitor is then directly also tied to the opamp output. This makes it so the opamp has a capacitive load and opamps are notorious to become unstable when driving capacitors. The trick is to add some resistance between the output and the capacitance which basically forms a basic 1st order low pass filter and "dampens" the connection to the capacitance.

[@portblock]

@@trevortjes op amps never my strong point, I was designing an ADC driver for a uController (my super strong point) and was having so many issue, this one video, I learned more than so many people try to over teach me. I was so close to your example. I just didnt have Cbig or injection R, Also I didnt realize some opamps are specific single supply and I didnt know the non rail to rail was so far off. Thank you so much for being selfless and putting these videos out. - gain I learned so much as you didnt over explain and you took it one step at a time. I watched all your op videos!

[@trevortjes]

@@portblock Yeah designing with opamps has so many caveats and overlooked details. Hence I made especially this video, I found that people and other videos don't pay enough attention to exactly this topic. Learning about it myself gave me that eureka moment. With this video I just hope to give people the headstart I never had.

[@ThiagoMeloDMA]

tks

[@pancajaya8530]

Great video

[@RSP13]

Brilliant!

[@mr.q7597]

Hi, it is so useful! By the way, any recommendation of the values of capacitors and resistors at 4:14?

[@trevortjes]

Both capacitors will add a high pass filter to your circuit, they both need to be fairly "big" to make sure your lowest desired frequency to go through unattenuated. For the resistors, do not go overboard, try to keep them under like 100k to minimize noise and other nasty stuff. Actual values depend on your desired bandwidth and gain.

[@mr.q7597]

@@trevortjes thanks a lot

[@mr.q7597]

@@trevortjes how about change the high pass filter which near Vout to low pass filter? Would it still remove the dc offset?

[@trevortjes]

@@mr.q7597 A little hint to never forget: think about DC as a signal with a frequency of 0Hz. A low pass filters passes all frequencies under the cutoff, a high pass filter passes all frequencies above the cutoff. High pass filters will neverpass DC, low pass will. So will a low pass filter remove a DC offset? No! Cause it gladly lets 0Hz go through.

[@lenturnbow8038]

@@mr.q7597A low pass filter would integrate the DC offset, not remove it.

[@CoderBittu]

2:32 What should be the approximate value of the capacitor connected across R2 and GND?

[@trevortjes]

Depends on your usecase and desired bandwidth. The higher the capacitance, the lower the cutoff frequency of the high pass filter. The cutoff frequency can be calculated as Fc = 1 / (2 * pi * R2 * Cimportant). For example, a 10k resistor and a 1uF capacitor will create a high pass filter at about 1.59Hz.

[@CoderBittu]

@@trevortjes Thanks

[@abdelazeemhassan3701]

Perfect

[@mohamdkazm576]

How to make synochroise circuit to ac signale . Thank you .

[@徐愷輪]

How about a dual supply circuit? How can I add dc offset to op amp schimmt trigger?

[@dooda1193]

goooooot

[@JohnUsp]

Awesome

[@bathong1519]

Sir, i calculated the transfer function of the Vo/Vi of the Op-Amp and realize that is the low-pass filter. Can you please show me your transfer function that proves it's a high-pass filter (the part that you says Cimportant )

[@lenturnbow8038]

Gain is Rfeedback/Rimportant, yes? Cimportant forces our amplifier gain to approach zero with falling input frequency because it is in series with Rimportant. Our amplifier gain thus increases with increasing input frequency. Just like a high pass filter, yes?

[@mgh9271]

any better choice for offset removal than cap?

[@trevortjes]

A capacitor is the best choice for removing DC offsets

[@MD-qz6gk]

@@trevortjes I heard that in nanoelectronics they use voltage traslator circuits with mos or bjt instead of capacitors. But I don't understand what are voltage traslator circuits.. or something like that...

[@MissionFitnessCTC]

Heel goed jongen!

[@QuyetHoang-zt5lo]

how to choose opamp type. assuming the input has a frequency of 100kHz

[@trevortjes]

Depends on many factors, if you only care for frequency (thus bandwidth), you have to check the bandwidth of the opamp. I made a video on this topic here: kzbin.info/www/bejne/b5yTmHqrm9h6odU

[@QuyetHoang-zt5lo]

@@trevortjes thank you

[@Krometheous]

Why do you want to isolate the DC signal if you're using it to offset?

[@trevortjes]

Imagine Vin already having a DC offset, you would have a battle between two DC levels and if you don't know what the details of the source of Vin is (like the output impedance but also the offset itself), you don't know who will win the fight and what the result will be. So we block that influence and uncertainty, and have a clean canvas to paint our intended DC offset on.

[@Krometheous]

@@trevortjes but how does a capacitor achieve this? And why do we sometimes use a capacitor in series with a resistor or the resistor is connected to ground and the other end is at a node meeting the capacitor?

[@trevortjes]

@@Krometheous Capacitors are physically two metal plates that are very close together but not touching. In fact this is just like cutting a wire in two and holding the ends very close together. How will current ever pass a cut wire? For DC it won't. For AC on the other hand, the alternating nature of the signal pushes and pulls electrons from one plate of the capacitor and in turn doing the opposite on the plate across the gap to compensate. So there you have it, DC having no way to go from one end of the capacitor to the other, and AC signals being "copied" onto the other side which makes it seem like it "passes" through the capacitor.

[@trevortjes]

@@Krometheous The resistors can have different purposes but the most common cases are for filtering or draining the capacitor. With the resistor it is possible to regulate the amount of filtering. The configuration of the capacitor and the resistor decides whether it is a low pass or a high pass filter. The combination of the capacitance and the resistance decides at which frequency the filter starts attenuating the signals. This point is the cutoff frequency. A resistor to ground at a capacitor can also be used to drain the capacitor when needed. If you got big heavy smoothing capacitors in a power supply, it is nice to have a way to quickly drain them so the user won't shock themselves (to death) when touching the electronics even after the connection to mains is broken. This is not always done tho and care should be taken when handling such devices. Usually we drain these capacitors ourselves by "shorting" the capacitor pins with a low value, high wattage resistor. But also in lower voltage audio you want to be able to drain capacitors to get rid of pops at startup etc.

[@RylanVlawgs]

I love you

[@CircuitShepherd]

Hello there 🙂

[@georgewinchester6403]

Καλύτερα από τον Σπασο τα λες, πιο κατανοητά

[@trevortjes]

Haha care to translate that to English for me?

[@georgewinchester6403]

@@trevortjes You explain a lot better than my professor

[@xoxo9623]

very informative, thank you!