Youtube series: The Operational Amplifier - From Abstraction to Reality

[ledtester]

Here is a new video series on op amps that I think would be especially of interest to advanced beginners:

https://www.youtube.com/playlist?list=PLu9wn21AYbaHVeWIdGNiLYFwbgOZsyjwK

It's presented at the 1st year college EE-level as it requires familiarity with circuit theory, RC and LC filters and Bode plots.

The series consists of 17 videos (so far):

- Op Amp History - The operational Amplifier - From Abstraction to Reality
- The Operational Amplifier - Abstraction Part 1
- The Operational Amplifier - Abstraction Part 2
- A Peek Inside the Operation Amplifier
- Understanding Op Amp Specs - Part 1
- Understanding Op Amp Specs - Part 2
- Op Amp Noise Calculations
- Op Amp Slew Rate Considerations
- Rail To Rail Op Amps - Advantages and Disadvantages
- The Perils of Resonant Decoupling Networks and Power Supply Rejection & the Magic 10R Resistor
- Op Amp Single DC supply Biasing
- Opamp Stability
- Reasons to Not Use a uA741 Op Amp
- Dealing With the Unused Amp in a Quad
- Cascaded Amplifier Cutoff Frequency
- Should I Use an Opamp for a Comparator?

There is one video which isn't in the playlist:

Compensating Resistor for Input Bias Current – Good or Bad? -- OldHackEE
https://youtu.be/7Qkoj3TJpKg

[philco]

Hi, Hopefully you could suggest a circuit? I'm working with non-inverting LM741 on breadboard. I have a voltage I want to drive a bar graph module with. this voltage comes out of a two way radio signal strength indicator line RSSI. Voltage range is 1.5 volts DC for no signal and ramps up to 2.5 volts DC for full signal. I'm trying to set a bias/reference so that the output of the 741 opamp gives me non linear amplification. between maybe 2 volts for zero signal and 6 volts for full signal. VCC on opamp is 7.5 volts. any help much appreciated, thanks.

[ledtester]

Hi, and welcome to the forum!

This question really deserves its own thread. Feel free to create a new thread with a descriptive title.

IIRC there is an online design tool for this situation. I think you can even choose which E-series to choose the resistors from. I think it was on ti.com -- I'll try to find it and get back to you.

[magic]

- Reasons to Not Use a uA741 Op Amp

I haven't watched those videos and I probably will not, but I can recommend them already 

Something for philco to consider too. With only 7.5V supply, signals close to ground, and presumably no negative supply, this won't work very well, but the common as dirt LM358 will.

Note that your LM741 may actually be LM358 inside if you have bought it from AliBayZon

[ledtester]

philco, here is a stackexchange question & answer which might be of help:

https://electronics.stackexchange.com/questions/34700/setting-lmc6001-offset-voltage

[jpanhalt]

Here's another circuit from Stackexchange: https://electronics.stackexchange.com/questions/30719/analog-voltage-level-conversion-level-shift

My voltage levels were 2.5V to 10.xV that I needed to scale to 0V-~5V for an ADC.  For the step down, I added a voltage divider.  You don't need to do that.

Note: That solution needs a rail to rail op-amp.

Edit: I have added an LTSpice simulation for that circuit.  LTSpice is a free program.  For some reason it opens funny on my PC, unless I start with Spice.  I post it, so you can easily change the op-amp to a 741 and mess with the resistors to get what you need.

[ledtester]

Simulating the LM741 in LTspice is a little tricky. You have to:

1. Download the lm741.lib file from https://www.ti.com/product/LM741#design-development (it's located in the PSpice Model (Rev. B) zip file)
2. Place it in the same directory as your .asc file
3. Add the directive: .include lm741.lib
4. Use the "opamp2" symbol
5. Go into the Component Attribute Editor and change the "Value" attribute from "opamp2" to "LM741".

Below is a modified .asc file using the LM741 along with the .lib file (which was named .lib.txt so I could upload it). I separated the power supply rails from V1 so you can more easily see how the rail supplies affect the output.

Also, in order to get the circuit to simulate I had to change the values of R3 and R4 from 100K down to 25K. R3 = R4 = 50K also works.

[philco]

Thanks everyone, that's really good info. The reason for me trying to use a 741 is that I can run it straight of the 7.5 volt radio vcc line and not have to add an extra reg to get down to 5 volts.
I'll have another go at this in the next week and post results.
A bar graph RSSI is really useful in my industry where signal levels from a tunnel leaky feeder system are easier to diagnose rather than trying to read a dBm level on a small two way radio screen and usually dark environment.

[bidrohini]

Thanks a lot for sharing.

[ledtester]

Just noticed that a bunch of new videos on op-amp noise calculations have been added to the series:

https://youtu.be/watch?v=koAdWJ0H9gU&list=PLu9wn21AYbaHZiqDUJywdIJ1tFg9xdZrL