I am working on a 400V step down LLC half bridge converter for a project. I am currently trying to simulate the circuit in LTSPICE and when I probe between the Gate and Source of the MOSFETs I see a lot of noise and ringing.





How do I deal with this?

 

There is no good to discharge gates directly thru D5,D6 without resistors.

Also Spice does’t like “floated” point like Vc. Tie the Vc thru 1Mohm to Gnd. (Maybe it helps with solving, maybe not. I am not sure).

You can’t connect Gnd of secondary winding with Gnd after rectifier.

 

C-5 and C-6 are guaranteed to aggravate Ringing problems, especially when turning-Off.

Why are they used in this Circuit ?
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C-5 and C-6 are guaranteed to aggravate Ringing problems, especially when turning-Off.

Why are they used in this Circuit ?
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A friend of mine said to add them to filter the input signal to the gate but I was sceptical about them..

 

Remove them immediately, they serve no purpose.

Doing this will also sharpen-up your Switching-Waveforms.

Your friend is clueless.
The reasons for adding Capacitance to a FET-Gate are close to zero,
except in very specialized Circuits where the Switching-Speed must be
slowed-down for a very specific reason.

R-8 ad R-9 are used to control Ringing in the Circuit,
the FET-Gate has it's own built-in Capacitance.
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