how to measure bode plot of Buck converter

[integ52002]

buck bode plot

Can someone please advice me how to measure the bode plot of the Closed LOOP Buck Converter. The loop consists of Error amplifier, the buck LC circuit and the comparator which sawtooth waveform is applied.
I am using HSPICE to measure it... But I dont know how.

I know how to get the bode plot for the Open Loop Buck converter, but when the error amplifier(compensation) is placed, I dont know how to do it this time.

Where should I apply the ac signal and where to measure?

 

[eem2am]

bode plot

if you try to acheeve stability then its ok...you dont need closed loop tx func.

you just need the open loop one...ie the combination of error amp and "control_to_output" tx funcs

then check the gain and phase margin there.

you can go on and plot the closed loop one, but it is of no use to you......you only need open loop one....and check gain and phase margs to see if its ok for you to close the loop.

you can calculate open loop one from the closed loop one

 

[Dmitron]

how to measure a buck

give it maximum load. than disconnect the load quickly and get oscillogram of SMPS output. Look at it form (you can translate it to frequency plot- bode plot that you needed).