Mosfet turning off resonance?

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MacIntoshCZ

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Hello,
I am curious what can be behind it? When turning mosfet off there is delay caused probably by oscilating gate capcitence with parasitic inductance. It oscilates at 8.7Mhz. Mosfet is close to driver few cm. Conected via 1r5. inductance is aprox 100nH. How it could be treated? Thanks a lot and sorry for hurting yours eyes when reading this horribly writed topic . 
 

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why did you blot out the RC network between drain and source? is it actually not in circuit? the RC network is a "snubber" and is intended to damp out oscillations
 
unclejed613 said:
why did you blot out the RC network between drain and source? is it actually not in circuit? the RC network is a "snubber" and is intended to damp out oscillations
Click to expand...
Energy from coil is recupereted back to vcc. Do not want to waste it... Its not in circuit.
 
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I placed 1n4148 across gate - ground U2,
DS3 with diode; DS4 without diode
yellow - U2 mosfet GS
blue - U2 DS
pink - transfomer pins 7-8
 

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What do you get if you substitute capacitors on the output of the gate drivers, rather than the actual FETs?

With caps of similar value to the gate-source capacitance of your FETs, you should be able to see how the drivers respond on their own, with no complications from FET drain (load) coupling.

If the waveforms are still messed up, it's some resonance in your circuit; if not, it's likely an effect caused by the FET drain-source capacitance, which opposes the gate drive as the FET switches fast.
 
Just assembled second board,
both traces are u2 DS
I would like to get to Mhz range,
Turn on time is 120ns, turn off 160ns
Do exist mosfet driver without current sink ? As i said energy is recuperated so push pull would not work. Using extra diode is waste of time.

 
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