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Reducing gate ringing of STD7NM80

Question asked by jansen.ronald on Apr 10, 2013

The image below is a piece of PCB layout of a flyback converter.


As the layout is important I inserted a picture. The red is copper on the top layer. Blue is copper bottom.
Problem I had with this converter is that the gate ringing was not only rather intense, but also every ms or so the ringing was even twice as high. Apparently it remained resonating for longer at those moments.
Now Increased the resistance for 22 to 47Ohms. The occasional very high ringing is now gone and the normal ringing is less intense than before. However, now I have the problem that the ringing remains longer. It now takes longer than the blanking period, and the MOSFET is switched of prematurely.

Question: how do I best solve this? I can make the Rgate even larger, but this will result in more switching losses. Does it also make sense to bypass the sense resistor with a 10nF to prevent the MOSFET source from being lifted up?