Following is the circuit I have been analyzing:

This is a buck regulator. Circuit description:
Input voltage : 12 V
Output voltage : 3.3 V
Feedback-path -> Combination of R1 and R2
Additional path -> Differential amplifier path that will be triggered once voltage across the sense resistor voltage is enough to turn-on the diode
Feedback voltage = 1 V


I am interested to calculate phase-margin and gain-margin. If any of you have much idea about transfer-function and feedback stability analysis, kindly advice.Please let me know if their is any further information required.

 

The attached paper is a good discussion about stabilizing switching supplies.
It's not a simple subject.
The analysis is done by linearizing the switching supply pulse-width-modulator as a linear amp with gain, with the feedback loop having compensation for the output inductor/capacitor, which forms a resonant circuit.

 

Measure phase margin time domain response -

http://cdn.teledynelecroy.com/files/appnotes/lab748.pdf

Perturb the loop with a load step response -

Regards, Dana.