question about component stress of 2 switch flyback in SpeedFit

WEN

Dear support team,

Could you help me to confirm that component stress in 2 switch flyback in SpeedFit.
I seem the waveform has 1700V blocking voltage when switch off.(demagnetization and Diode clamp to VBUS.)
Why the SpeedFit show blocking voltage is 850V and recommended component utilize 1200V device in initial configure?

I also attached the Speedfit result, please review it.

SpeedFit Silicon Carbide (SiC) Design Simulator _ Wolfspeed.pdf

Forum_Moderator

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

Mhusain

Hello Wen,

Thank you for your question. During the off period when the MOSFETs are switched off, there’s a moment when current is still flowing in the secondary side. At this time, the output voltage of 48 volts is reflected in the primary of the transformer, resulting in 1440V (48V * 30). The two devices then need to block a total of 3140V (1440V + 1700V), which means each device must handle 1570V. However, once the current in the secondary diminishes, the voltage that these devices need to block reduces to the input voltage of 1700V (850V per device). This is what you observe in the MOSFET voltage waveform.

I hope this answers your question. Please feel free to reach out if you need any further assistance.

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.