I wish to learn about op-amps not sure Where/How/What to start with ?

[anishkgt]

Hi All,

Please be easy on me ! ! !

I am trying to learn how to use an op-amp and Dave's video is a little too much for me to grasp. From other videos i could understand that by giving two voltages at the inputs i could get one output, a low or a high. To make it simple i would not get any formula at first so am looking forward some practical knowledge first and on the way ask questions and learn.

Could anybody recommend some links to where i could some info and which op-amp IC's to buy to get more practical knowledge on it as well. while bread boarding.

[kalel]

There are some opamp circuits you can experiment with here:
http://www.falstad.com/circuit/e-index.html

They aren't practical examples, though. Trying some examples on a breadboard definitely sounds better. I should do it too at some point.

[hamdi.tn]

Hi,

Texas instrument has a nice book about opamp.

https://focus.ti.com/lit/an/slod006b/slod006b.pdf


Hamdi

[bjcuizon]

Try to look at this thread and its collections. Well, it might be kinda in-depth for you but anyhow, it might be useful.
https://www.eevblog.com/forum/beginners/opamps-for-everyone-pdf/

[Mephitus]

A youtube video that finally made op amp theory click was this one:

[Avacee]

Whilst it was Dave's EEVBlog #600 that clicked Op-Amps for me this series of videos by RSD Academy starts from the very basics of Op-Amps and doesn't descend into the dick-swinging complex maths that many others youtube creators think make them look smart but aren't smart enough to realise they're completely failing to educate or impart any wisdom.
This series is similiar to Dave's but in a very long and verbose format and worth sticking with if Dave's hasn't worked for you.

https://www.youtube.com/playlist?list=PLL_nf1OmixTTd7rEoqoM6aJ5ZdI-V47vs

[rstofer]

I suggest you learn by playing, it always works for me!  I'm a hands-on kind of learner.  I like to touch and feel.

So, what tools do you have for experimenting?  Do you have any op amps?  You will clearly need some kind of power supply (don't overlook 6V worth of batteries), and a multimeter.  If you have both a positive and negative supply, things are a little easier to explain because your inputs are swinging around 0V.  If you only have a 6V battery then we need to talk about a virtual ground formed with a couple of resistors.  We can get into that when you start picking an op amp.

For dual supplies, the LM358 works well.  For a single supply, there are recommendations in Chapter 4 of "Op Amps For Everyone" and I'm too lazy to go look.  You can even get 4 op amps in a single package - that's kind of cool.

My only interest in op amps is for their original intent.  They were invented specifically to perform analog computing and that's where I have used them.  I like solving certain kinds of problems using old fashion technology (with modern components).  So, analog integrators...

[w2aew]

Hi All,

Please be easy on me ! ! !

I am trying to learn how to use an op-amp and Dave's video is a little too much for me to grasp. From other videos i could understand that by giving two voltages at the inputs i could get one output, a low or a high. To make it simple i would not get any formula at first so am looking forward some practical knowledge first and on the way ask questions and learn.

Could anybody recommend some links to where i could some info and which op-amp IC's to buy to get more practical knowledge on it as well. while bread boarding.

Here's my tutorial on op amps - only 13 minutes long, been viewed over 400,000 times:

[Ian.M]

For a light on maths hobbyist friendly OPAMP book, take a look at
Forrest M. Mims III's 'Engineer's Mini Notebook: Op Amp IC Circuits', originally published by RadioShack in 1985.   Understandably the chips it uses are a bit dated, but its still a good intro if you don't want to do much maths.

[anishkgt]

Thanks guys appreciate all the links.

So is it necessary that Op-amps require a negative volt ? then i need to get a power supply like this
https://www.amazon.com/Rigol-DP832-Triple-Output-Supply/dp/B00ENX02GC

at the moment i have a basic variable power supply like this
http://www.ebay.com/itm/Buck-boost-Power-Supply-module-LCD-color-display-voltage-conveter-/182462594377?hash=item2a7b9e3d49:g:heIAAOSwWxNYrBEW

[Ian.M]

While OPAMPs don't actually *require* a negative supply, not having one makes a lot of circuits that use them more complex or harder to understand.  If you are dealing with high gain OPAMP circuits, a cheap switched mode PSU with 100mV output ripple like that EBAY one is undesirable. 

The 'classic' OPAMP supply would be a center-tapped secondary 18v-0-18v or 20V-0-20V transformer feeding a bridge rectifier, reservoir caps and a well heatsinked pair of 7815 and 7915 regulators.   The +/-15V rails are safely under the +/-18V supply limit of many older OPAMPs but still allow +/-10V signal swing with plenty of headroom.

For breadboarding, you could do a lot worse than two cheap alkaline 9V PP3 batteries, with a red lead and a black lead from the two battery clips connected together for 0V and the remaining leads run via a DPST switch so you can switch the +/-9V rails on or off simultaneously.   If you use higher current batteries than PP3, then you should fuse *BOTH* the positive and negative rails at no more than 500mA.

[anishkgt]

Well that was quite interesting and something new to learn. I am just starting with electronics but when i say starting i've completed a spot welder project (https://georgehobby.wordpress.com/2016/11/09/diy-arduino-based-simple-spot-welder/). So just saying am not very new to it.

So I've been trying to learn op-amps and implement it into my next version of it. Correct me if am wrong i understand that negative feedback can be used as a reference voltage for potentiometers or others that require it. So a reference voltage is actually used so that the devices that uses it will get a continuous supply no matter how the voltage is at the input of the op-amp.

[w2aew]

Thanks guys appreciate all the links.

So is it necessary that Op-amps require a negative volt ? then i need to get a power supply like this
https://www.amazon.com/Rigol-DP832-Triple-Output-Supply/dp/B00ENX02GC

at the moment i have a basic variable power supply like this
http://www.ebay.com/itm/Buck-boost-Power-Supply-module-LCD-color-display-voltage-conveter-/182462594377?hash=item2a7b9e3d49:g:heIAAOSwWxNYrBEW

Here's a video I did on the subject of op amp power supplies.  In a word - no, a negative supply isn't absolutely necessary - you just have to take care in the input and output voltage ranges vs. the supply rails:

[rstofer]

And you may have to create a virtual ground at the + input using a pair of resistors that divide the power supply voltage in half.  See at 3:00 in the w2aew video earlier.

[Ian.M]

There's also specialised rail splitter ICs like the TLE2426 which provides  a much 'stiffer' virtual ground at half the supply voltage than a simple resistive divider can without an excessive standing current.  Subject to its power dissipation limits, the TLE2426 can handle +/-20mA of virtual ground current.
Its available in a number of packages including breadboard friendly TO-92 and 8 pin DIP.
Unlike an OPAMP rail splitter, it tolerates large decoupling caps on its output.

[rstofer]

Khan Academy has a series of videos re: Op Amps
Here is the first:

https://www.khanacademy.org/science/electrical-engineering/ee-amplifiers/ee-opamp/v/ee-opamp-intro

In this first video, the discussion is about dual supplies.  I don't care for the bit where the presenter draws a ground connection to the op amp, no such thing exists.  But it does point out that the output is still referenced to ground.

As a rule, the Khan Academy takes a very deliberate approach to presenting material.

[anishkgt]

So is resistor divider just a point between two resistors to get a voltage drop or is there anything else to it ? I see one side of two resistors in series connected to Vcc and the other end to GND. A reading take from the center, so what is the point of having the second resistor connected to GND.


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[rstofer]

So is resistor divider just a point between two resistors to get a voltage drop or is there anything else to it ? I see one side of two resistors in series connected to Vcc and the other end to GND. A reading take from the center, so what is the point of having the second resistor connected to GND.


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With a single supply, say 12V, the two resistors in series will draw a certain amount of current.  Let's say the resistors are 1k so the total is 2k and there will be 6 mA flowing.  Now, that 6 mA flowing through the bottom resistor drops 6V and voila', we have divided our power supply voltage in half at the junction.  We call the junction a virtual ground.  Everything from now on will be referenced to that virtual ground.

Now we apply the virtual ground to the + input and we can accept incoming signals from about 2V to 13V (depending on the op amp).  But note that the incoming signal on the - terminal has to be centered around the 6V on the + pin.  Achieving that is a separate issue.  If we really want to measure an AC signal, we will have to bias it up by 6V DC.  Later on you will run into capacitive coupling.  Basically, another voltage divider but with much higher resistor values (so as to not load the previous stage) and a capacitor.

It is so much easier to wrap your head around op amps with dual supplies.  Then you can accept inputs between perhaps -10V and +10V and your AC signal doesn't need to be offset.  BTW, there's a reason that Analog Computers using integrated circuit op amps use +- 15V supplies and generally have signal swings between +- 10V.  That leaves plenty of headroom on both ends to keep the op amps from saturating or going non-linear.

I would try my very best to have dual supplies.  In the early days it is so much easier to understand what is going on.  Yes, I know, almost all op amp circuits today are using single supplies.  Well, sure, they're designed by pros!

[b_force]

My advice on learning; just start building stuff!

Build little circuits and thinks and try to understand the schematics. 
After a while you bump into little issues, have a little google search, questions on forums etc

[anishkgt]

Yea building one does help. Any specific op-amp that I should buy for my needs just learning for now.


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[Ian.M]

https://www.eevblog.com/forum/beginners/rail-to-rail-op-amp-for-a-beginner/
I strongly recommend choosing ones rated for at least 20V total supply voltage (+/-10V) simply so you can easily use them on a dual 9V battery supply,   Low voltage OPAMPs are a PITA when you are trying to lean and combine them with other circuits, however its useful to have ones rated for a minimum supply voltage low enough to permit 5V single supply operation if you want to interface with Arduinos or other MCUs.

Also read Op-Amps that Do and Don't Phase Reverse and if in doubt Google: <part_num> phase reversal

[vk3yedotcom]

Some notes from Talking Electronics http://www.talkingelectronics.com/projects/OP-AMP/OP-AMP-1.html

[anishkgt]

I would be using these with an arduino. So i should be picking something in 5v range, correct ?


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[rstofer]

Pay attention to Figure 4-7 in "Op Amps For Everyone"  See how that TLV2472 works to the corners and the others fall apart?

https://focus.ti.com/lit/an/slod006b/slod006b.pdf

You will need to use rail-to-rail input-output op amps like the TLV2472 family or you won't be able to get very close to the rails (+5 and Gnd).  If this is the case, you lose bits of resolution.

http://www.ti.com/lit/ds/symlink/tlv2474a.pdf

I have used the TLV2474 and it worked well.

[ez24]

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