Phase margin in laplacian equations

[goldsmith]

Dear LvW
Hi
Thanks for your Good Advice . i think that you're right. i love learning new things , but when i read some books , those was complicated. and was not practical. i will be happy if you introduce some books in this area . i'm new to control systems and loop stabilization. but not in all of electronics. :smile: and i want to learn new things , but i don't know how can i find the name of practical books in control systems and loop stabilization. is it possible that you guide me to find the name of practical books in this area, please? if you help me to find the name of , them , i will buy those books and i will read all of them , fast and carefully. i love reading good books in electronics .
Again thanks for your helpful advice.
Sincerely
Goldsmith

 

[LvW]

Dear Goldsmith,

I am afraid not to be the right person to recommend suitable books in english (I am german).
I am sure that some other forum members could give you some good recommendations.
Nevertheless, some comments to your last posting:
Before studying loop stabilization and related areas you must become familiar with more basics.
Here are some keywords:
Feedback (why?) , loop gain, feedback factor, phase/gain margin (why?), oscillation condition, Bode Diagram (principle),
complex frequency s, meaning of poles and zeros, Nyquist diagram,...

 

[goldsmith]

Dear LvW
I want to give promise to you , that i learn things that you suggested to me perfectly and carefully and fast.
Again thanks for your patience and guidance.
Yours Sincerely
Goldsmith

 

[biff44]

Confusing thread.

The bode plot of that ideal op amp will show gain starting at low frequency being RF/Rin=R5/R1=1. At the frequency where R5 = 1/2PiF, the gain will be 3 dB down and -45 degree phase shift. after that the gain drops 20 dB/decade and the phase eventually reaches -90 degrees.

From the above, you can easily sketch the Bode diagram.

For an ideal op amp, there is no calculation for phase margin...it is stable at all frequencies.

IF you want to draw a real world Bode diagram for a real world LM118 op amp, you need to go to the data sheet and figure out the internal poles and zeros of the op amp, and include any load reactance too, to figure out a phase margin.

If you used that op amp circuit in a bigger feedback system (for instance adding a motor for a load and a position sensor as the input), then you could talk about system phase margin in a more meaningful way.