#1132 Using offset voltages and op-amps

Episode 1132
I show two ways to apply an offset voltage to a circuit. I change a 0 to 2 volt signal into a +4.7 -4.7 volt signal

[potatospade]

I’m very new to electronics and have been learning about op amps. I’m designing a circuit where I need to scale a control voltage of 0-5v to -4v to 4v. I’ve scoured the web trying to figure it all out and finally came across this video. You have explained it so clearly, I now know exactly what I need to do. Thank you so much!

[therearelights]

Great explanation! I remember op amp circuit design being my favorite in college. Back then they seemed to operate by magic. Now after a couple of decades in the field, experience has taken some of that 'magic' away, but they're still my favorite thing to play with even today 😁

[td]

I watched this, again, for a different use. Meaning, this video has excellent reference material/information. Thank you, again.

[nickcaruso]

ah you answered my question- the resistors on the inputs set weights. thank you. great video.

[NickElectronics]

Usefull video, thanks. Op amps are really amazing, but tricky:) All this feedbacks, different circuits you can make with them. It takes time to understand them and much more time to learn how to calculate them)

[saturntony]

Or at 7:48 like us guitarists as well as electronic people like to call it, a mixer 😊 thanks for sharing 👍

[dalenassar]

If you go through the mathematics, you find that NEITHER of these circuit configurations allows gain AND offset to be independent! For this you need TWO op amps....

1) first amp is connected as an inverting amplifier with FIXED input and feedback resistors with the variable offset voltage (Voff) applied to the non-inverting input. You get an offset of 2Voff (I may have to have to check this) at the output.

2) Then you feed this op amp's output into a standard inverting amp and adjust the gain resistor (Rf).

3) The two op amps MUST be connected with the offset amp feeding the gain amp.

Also, this gives an output that is not inverted!

[byronwatkins]

In the second circuit, the input has Voff reference while the output is still ground referenced; this is why the offset is not 1 V. If the inversion is not desired, you can always use a difference amplifier, apply the signal to the + chain, and +1 V to the - chain.

[jafinch]

Great info, thank you sir. Has me thinking about and thinking I'll need to review again for potential cost effective designs for DIY DCEP & DCEN offset adjustments for an AC (I think is pulsed DC technically albeit with potential range of waveforms?) welding aluminum option on an older machine that doesn't have the nicer frequency and offset controls. I still haven't gotten to reviewing the schematics of the original Miller Synchrowave design(s), since when I get around to again I wanted to start from basic theories/apps. Very inspirational thought provoking where I'm guessing will be done using transistors for higher current applications since I don't recall ever seeing a higher current capable op-amp.... where like transistors one could arrange in parallel even to deal with the current needs.

[mk]

Also see w2aew's video: #328: Circuit Fun: Op Amp Signal Conditioning - a Practical Example

[magnuswootton]

you can see on the output of that amplification its 100% PERFECTLY linear.

[dalenassar]

GREAT VIDEO!!!!
I did as you suggested and "built it myself". Incoming question....instead of the 47k resistor, I used a 100k pot in order to adjust the gain, along with the variable offset, as you did, on the "+" input. My goal was to make an op amp with INDEPENDENT gain and offset. When I adjusted the gain, I think the offset was changing as well. Soooo, with this circuit, is the offset supposed to alter (at all) when the gain resistor is Or should they be 100% mutually independent.
I did have sort of a 'rat's nest' breadboard with no filter caps.
YOUR REPLY WILL BE GREATLY APPRECIATED AS I AM IN GREAT NEED OF SUCH A CIRCUIT!!!

[hardkore]

Great video! Thanks for uploading.

I'm currently troubleshooting an op-amp which has a constant bias input of 2.56V at the (+) input pin, and NO SIGNAL on the (-) input pin, yet I am still getting 2.56V at the output of the op-amp. The op-amp supply rail is +8V and -8V and tested out to be just fine with or without the op-amp in circuit so I have eliminated the supply voltage circuit as an issue. In your experience with faulty op-amps, have you ever run into this scenario?

[Jesception]

Question; the opamp itself is also powered by -12/+12 right?

[ebones]

In the inverting op amp example you have the + input grounded. In some circuits this + input is grounded through a resistor. What is the purpose of this resistor? My circuit example is used as a meter scaling circuit, where a voltage drop across a resistor is amplified to drive an analog meter.

[therealspixycat]

Is this also an option to correct the Vos offset voltage? Or do I need an opamp with a specific 2 pins to correct the Vos offset? Thanks!!

[rudrakshavegad]

Hello sir, I need some help, the thing is whenever I make any op amp based circuit in any basic op amp configurations I have a problem at a specific time that is when the circuit is powered on or powered off at both of these instances the output of a op amp is very unpredictable or sometimes wierd voltage fluctuations but the circuit works perfectly when powered, please help how can make it work reliably at these instances

[td]

Thanks! I know that your example was for a motor. However, if you wanted to use this circuit with audio, what are the considerations of having added DC offset? In other words, I know that DC offset is bad for speakers... So, what is needed to prevent that damage, if this circuit is employed?

[nickcaruso]

so I have this background obsession with dc (stepper) motors, where i noticed as a kid that if you connect the windings, and turn one, the other will turn because of the energy generated by the other. But obviously it's not much power and the motors will slip and miss steps. I've always thought that it should be possible to add power to the circuit with op-amps and comparators, to "stiffen" the response... but I don't quite know how to do it. Is this something you would be interested in explaining/investigating?

[qwertyuiop]

Hello, i would like to ask you if is it possible to realize a simple circuit that i have in mind. I have an arduino that can menage Voltages between 0 and 5 V. I just bought a little ADC module that can performe 12 bit conversion to get signals like LFO for musical purpose. What i need here is to tranform voltages that goes from 0 to 5Volts to something like -10 to + 10Volts. I have a dual power suplly -12 to +12Volts. If i understood i need to build that circuit with an amplification gain of something like 4. Hope you can help me

Thanks