How to break circuit and add PAC source to get open loop gain plot in PAC analysis

[walker5678]

I want to plot the open loop gain dB20 and phase curve of a DC/DC converter using PAC analysis, but how to break the circuit and add PAC source?

You cannot insert a L-C filter to isolate AC signal and pass DC signal, because the PSS analysis need to do transient analysis first, if you insert filter the transient analysis is not correct.

How to solve this problem?
Thanks.

 

[FvM]

I'm not familiar with PAC analysis, but a general method is to insert a series voltage source in the feedback path and calculate the loop gain as ratio of voltages at both sides.

 

[shar2013]

It is actually two stage simulation :
1. You add the series current source as mentioned above calculate Tv=-Vy/Vx. Vy ---- (-)||(+) ---- Vx

2.You replace the series voltage source with a shunt current source and calculate Ti=iy/ix

iy --|-- ix
|
^
|
|

The the open loop response is T= (Tv*Ti-1)/(Tv+Ti+2)

it is called Middlebrook method.

Good Luck !

 

[FvM]

It is actually two stage simulation

Not generally. If you have a circuit branch with Zsource << Zload, it's just one step. In most active circuits, this is feasible.

Also Middlebrook is describing the method initially as using either voltage or current injection, with respecitive prerequisites for the circuit topology. **broken link removed**