#### dracarys99

##### Newbie level 5

Input voltage 400 V, Output voltage 200 V, Output power = 100 W, L = 100 uH, C = 4.4 uH, switching frequency = 300 kHz.

I need the open loop transfer function of this, and it should be similar to the one I plotted on MATLAB using the transfer function I derived. However, there is something going wrong in my Pspice simulation. The bode plots aren't matching at all, and even the bias points are wrong! The circuit is not wrong I think, because this works with any other buck circuit values giving the correct bias points and bode plots also. Here is the circuit (which works correctly for this one here Duty cycle = 0.5):-

But when I change the values to my synchronous buck circuit:-

Since it works on all the other circuits (literally any), I'm not sure if it has something to do with the U3 definition. Here it is:-

According to my calculated control-to-ouptut transfer function, there should be a 32dB overshoot at 7.57 kHz, I don't get that either in the bode plot from this AC analysis.

Here is the Pspice one:-

And here is the MATLAB one using the derived hand-calculated transfer function:-

What am I doing wrong?