C3M0075120J behavior in LTspice .AC analysis

Jinyuan

I'm new in Power Electronics. When I was simulating the Class Phi2 converter and plotting the impedance plot, I encountered the issue mentioned in the title: Unsupported mixture of time-dependent and arbitrary behavior in .AC analysis. However, I did not encounter this issue when using other MOSFETs, such as C3M0065090J.

In the circuit, I have already removed the pulse power source, and the only difference is that I replaced C3M0065090J with C3M0075120J. Could there be some code in the library that does not allow AC analysis? How should I fix this issue?

Forum_Moderator

Thank you for your post, it has been approved and we will respond as soon as possible.

Mhusain

Hello,

I have modified the model (C3M0075120J_ConstantCgd.lib) to work in .AC analysis. The issue was caused by the nonlinear model of Cgd and to resolve this, it was replaced with a constant capacitor model. I have also attached the simulation results with the .AC analysis.

C3M0075120J_ConstantCgd.lib

For transient analysis, please use the device model with nonlinear Cgd model (C3M0075120J.lib) provided below.

C3M0075120J.lib

Let us know if you need further assistance.

Regards

Jinyuan

Hi,

Thank you for the modified libary! I can do the AC analysis now. But there's also another question I found in the simulation. Like in the screenshot, It seems like the parameters are suitable for ZVS condition, but in transient analysis, the Vds waveform doesn't go smoothly. Does this happen because of the Rgs or Coss or anything else?

Jinyuan

Hi,

Also I found it won't work (stop at around 85ns) if I turn the Rgs to 0ohm-5ohm when I doing the transient analysis. Is that because of the limit current of Ig in the device?

Mhusain

Hello,
Thanks for checking out the model. I have made some updates to improve its convergence under the given conditions. The revised version should now simulate correctly for transient analysis. I have attached the updated model along with the simulation results for reference. You can also use the model available in the native library under Component(P)-> [Contrib]->[Wolfspeed]->[Discrete] for transient analysis. Let us know if you run into any further issues or if there is anything else that could be improved.

C3M0075120J.lib

Regards

TBhatia

Hi, I hope that this answered your question. I will close this discussion for now but if you have a follow up question, please "Start a New Discussion" and we would be glad to support you further.