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Clamping MOSFET voltage using snubbers (TVS)

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zuq

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Hi guys

In a typical buck/boost converter if you have a free wheeling diode across the MOSFET, can there still be over voltage across the FET? how? would you still need to add a separate clamping diode across it?

Cheers
 

Dear Cheers
Hi
where is your schematic? there are more arrangement of buck boost converter available .
Best Wishes
Goldsmith
 

Hi goldsmith, here is the image. it is actually a DC motor drive, essentially a buck converter. Thanks
drive.png
 

Dear zuq
Hi
Are you sure that this circuit is ok for your aim? i don't think that! a simple H bridge arrangement or a simple Half bridge arrangement can be ok for your aim . meanwhile about the cage motors : the frequency and the voltage should change with together ( for controlling the squirrel cage motors).
Best Wishes
Goldsmith
 

Dear goldsmith;

Sorry about the confusion,
This is a PMG DC motor hence I dont need constant V/F. Back to the topic :D, any ideas?? Thanks
 

so I dont need TVS across MOSFETS since I have free wheeling diodes??

How about the DC bus?? due to lead inductance there will be over voltages on the bus. I can add DC bus caps to reduce that but large dv/dt is not good for caps (high currents).

How do I perform calculations to select the TVS?? based on over voltage?
 

ِDear zuq
You can use a simple snubber network to be ensure that your system is protected!
Best Lucks
Goldsmith
 

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