Mosfet turning off resonance?

Status
Not open for further replies.

MacIntoshCZ

Active Member
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 . 
 

Attachments

  • IMG_20210129_175536.jpg
    4.4 MB · Views: 200
Last edited:
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.
 
Last edited:
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
 

Attachments

  • RigolDS3.png
    78.9 KB · Views: 177
  • RigolDS4.png
    81.3 KB · Views: 177
Last edited:
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.

 
Last edited:
Status
Not open for further replies.

Similar threads

P
  • Locked
  • Question
Modify circuit to power on/off Attiny85 by remote
Replies
16
Views
2K
Nigel Goodwin
A
  • Question
Turning Nokia hhd into precision motors for micro camera gimbal
Replies
5
Views
1K
avbs18289
A
  • Question
OFF-the-wall idea for momentary ON switch
6 7 8
Replies
148
Views
16K
JimB
S
  • Question
isolated DC-DC convertor and mosfet driver
2
Replies
28
Views
4K
shortbus=
S
F
  • Question
Making a timer on delay and off delay without microcontroller
2 3
Replies
43
Views
5K
Tony Stewart
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…