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-   -   How to model stability analysis of a linear regulator such as this? (http://www.diyaudio.com/forums/solid-state/226848-model-stability-analysis-linear-regulator.html)

 Fusion916 1st January 2013 11:03 PM

How to model stability analysis of a linear regulator such as this?

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In simulation, what is the proper method to model a stability analysis of the following circuit?

Meaning where do I inject the AC signal and where do I look at the loop gain/phase? Do I need to inject the AC signal into vdc and look at vb? If so, what other modifications do I need to make to my testbench to properly model the analysis?

 Elvee 2nd January 2013 07:34 AM

The most straightforward way (not 100% theoretically accurate, but more than sufficient) is to insert your AC source between FB and the NI input, and look at the ratio of VFB/VNI

 Fusion916 2nd January 2013 05:00 PM

Quote:
 Originally Posted by Elvee (http://www.diyaudio.com/forums/solid-state/226848-model-stability-analysis-linear-regulator-post3307620.html#post3307620) The most straightforward way (not 100% theoretically accurate, but more than sufficient) is to insert your AC source between FB and the NI input, and look at the ratio of VFB/VNI
What inaccuracies arise from this method?

 jcx 2nd January 2013 05:14 PM

use forum search for Tain Middlebrook LoopGainProbe for some discussions

you can also force the output with a Isource - the impedance curve is related to the feedback factor - severe peaking is a warning sign

load step response gives similar info

 Elvee 2nd January 2013 05:30 PM

Quote:
 Originally Posted by Fusion916 (http://www.diyaudio.com/forums/solid-state/226848-model-stability-analysis-linear-regulator-post3308153.html#post3308153) What inaccuracies arise from this method?
The loading of the divider by the amplifier's input is not taken into account

 Fusion916 3rd January 2013 02:52 AM

Elvee, do you mind posting a simulation schematic of your test circuit for stability analysis?

 Devilsdance7775 3rd January 2013 06:54 AM

I bet MicroCAP does it. If you install it and go to EXAMPLES folder than you find something similar ( stability over time, outside temperature, parts parameters deviations and transition events). Must be here.

 Elvee 3rd January 2013 08:23 AM

2 Attachment(s)
Quote:
 Originally Posted by Fusion916 (http://www.diyaudio.com/forums/solid-state/226848-model-stability-analysis-linear-regulator-post3308848.html#post3308848) Elvee, do you mind posting a simulation schematic of your test circuit for stability analysis?
Here it is; the circuit had to be adjusted to display something usable as the original values were too crazy, but the principle remains the same whatever the exact circuit.

 Fusion916 3rd January 2013 05:30 PM

V3 is the AC source correct? And what purpose does the 1n4148 serve?

 Elvee 3rd January 2013 06:48 PM

Quote:
 Originally Posted by Fusion916 (http://www.diyaudio.com/forums/solid-state/226848-model-stability-analysis-linear-regulator-post3309622.html#post3309622) V3 is the AC source correct?
Yes
Quote:
 And what purpose does the 1n4148 serve?
Displaying a nice downwards sloping curve as expected, instead of an ugly flat one (not connected with simulation issues).

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