# Pspice giving wrong results

I have a ZCS buck circuit which I simulated on PSIM first, and wanted to simulate it in Pspice now with the real components. However, I am getting wrong results in Pspice, and I can't figure out why. Here's the Pspice circuit followed by PSIM,

Here are the same quantities (VGS and switch current) plotted in PSIM(correct) & PSpice(Wrong!).

Although my sawtooth voltage source output is correct (200 kHz, 3V peak) here is the way I defined it in Pspice:-

What's going wrong in my Pspice simulation?

EDIT 1: I did not correctly add the gate drive isolation!! Problem solved.

• How do you know which of the simulations is "correct"? Feb 22 at 15:54
• @sm32 define 'correct results' Feb 22 at 16:17
• @ElliotAlderson I reckoned PSIM results to be correct because it worked according to my calculations and it is indeed giving the ZCS actions, while in my Pspice circuit it didn't.
– SM32
Feb 22 at 18:46

It's never a bad idea to avoid blaming a tool that's widely used in the world by engineers all over and, instead, to doubt your actions. In this case you used an opamp instead of a comparator, while in PSIM you used a buffer to condition the signal. That can result in widely changing output. Be sure to use a comparator, and also that it uses the correct output levels to drive your switch. In other words, make sure the two schematics are the same, if you want similar results.

And if the sawtooth is not working, try using a PULSE source with V1=0, V2=3, Ton=4.99u, and T=5u. Not lastly, are you sure you want those values for the loop filter: 10 Ω, 24 Ω, 6 μF, 20 μF?

• I see, I'll keep that in mind. However, I did get my Pspice circuit also working by adding the isolation to the gate drive. The sawtooth worked fine, I was wondering if anyone would tell me how to do it differently.
– SM32
Feb 22 at 18:51