FRA question

Figured that part out.  Looks like the program is intended for switching regulator design?  Not what I had in mind.  Looking for frequency response of op amp circuits.  Haven't figured out how to get that.

Hi fatz ,

You can use a simple AC analysis for that.

https://www.analog.com/en/education/education-library/videos/video-series/ltspice-ac-noise-analysis-tutorial.html

here are some videos regarding this function.

Thanks.

Regards,

PaulDaria 

I duplicated the circuit in the tutorial using an LM308.  Could not get that to run.  Got a message that it needed an ac source.  Put that in.  Got the same result.  What am I doing wrong?  Put the ac source in the input.  Maybe it goes in series with the FRA?  Will try that next.

Hi fatz ,

Please share you application Circuit. when using AC analysis, you no longer need the FRA symbol.

Regards,

PaulDaria 

No go with the ac source in series with the FRA.  This is frustrating.

Thank you for your reply.

I will share the circuit with you when I figure out how to do that.  I tried using the circuit without the FRA symbol, but that did not work.  I duplicated the example, pretty much, without any success.  The example uses the FRA symbol, BTW.  Somehow I found a way to insert the ".ac oct..." line, but I am not sure how I did that. 

The last trial, without using the FRA symbol, did not work.  Leaving the cursor on the Run symbol showed (in the lower left of the screen) that the program was determining the initial conditions.  That notice disappeared after a few seconds and the "run" notice came back up.

It is getting past my bedtime, so I will pursue this tomorrow.

Paul

Here is the circuit.  I think.  It is a bitmap, the window says the "url protocol is not allowed."  I printed the circuit, then scanned it in Photoshop elements.  Then poked the "insert" button.  What are my options?

I appreciate the time you have taken.  This is frustrating.  One of my first jobs was designing a thrust rating computer for the DC10.  We called it a "frustrating computer."  That term applies to all computer related things, now.

Fatz

Got it running.  Just need to understand the plots.

Thanks, Paul, for your help.

fatz

Hi fatz ,

It good to know that everything are all good now. 

Thank you for using LTspice and happy simulation.

Regards,

PaulDaria