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  1. #1
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    Serious IGBT overshoot

    Hi Everybody!

    I'm working on a power-supply but have run into some serious overshoot problems. As you can see I tried with a RCD snubber, but that didn't change anything, do you perhaps have any suggestions how to deal with this?

    Click image for larger version. 

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    Click image for larger version. 

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    Regards Svend.

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    Re: Serious IGBT overshoot

    Where are your decoupling caps?

    Where is your waveform from?

    Where is your PCB layout?

    Where is your overshoot?

    What are your driving signals?



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    Re: Serious IGBT overshoot

    Your circuit and scope trace is not understand able as presented. Please add details to better explain the problem, the investigations done, and the results obtained so far - with proper cross reference to your diagrams.



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  4. #4
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    Re: Serious IGBT overshoot

    Hi barry

    Quote Originally Posted by barry View Post
    Where are your decoupling caps?
    I don't have any yet

    Quote Originally Posted by barry View Post
    Where is your waveform from?
    It's generated by a microcontroller, then entering a driver that is connected to the on/off resistors R3-6

    Quote Originally Posted by barry View Post
    Where is your PCB layout?
    I don't have any, it's a bird nest, no breadboard, only soldering.

    Quote Originally Posted by barry View Post
    Where is your overshoot?
    I don't know if I used the correct technical term, so I have marked it in red.

    [QUOTE=barry;1649665] What are your driving signals?

    I'm using 1EDC20I12AHXUMA1 as driver with single supply +15V, and the outputs are connected to the on/off resistors R3-6

    Since my last post I removed the RCD snubber and changed values of R3-6, then I got rid of the turn-on "overshoot", but I still have a problem with turn-off.

    Click image for larger version. 

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    The yellow trace is "OUT" and I'm using a 1000x probe, so you have to multiply by 1000

    Click image for larger version. 

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    Re: Serious IGBT overshoot

    Quote Originally Posted by kripacharya View Post
    Your circuit and scope trace is not understand able as presented. Please add details to better explain the problem, the investigations done, and the results obtained so far - with proper cross reference to your diagrams.
    Hi kripacharya, please see my reply to barry



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  6. #6
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    Re: Serious IGBT overshoot

    No decoupling caps and no PCB, and you're wondering why your circuit works like crap???

    You probably have a LOT of stray inductance, not to mention inductance from the ground probe of your oscilloscope.


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    Re: Serious IGBT overshoot

    I see you are switching on & off quite slowly with those high-ish gate resistors - but you still need 1uF 630V say across the pair of IGBT's from top collector to bottom emitter to soak up the turn off wiring inductance energy - without seeing the entire schematic and a picture of the hardware - it is hard to make positive suggestions ...

    - - - Updated - - -

    zoom right in on those over shoots for a good look ( 500nS/div & 100nS/div ) it may be just CM pickup ... how many amps are you trying to switch ?


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  8. #8
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    Re: Serious IGBT overshoot

    Hi Easy peasy!

    Quote Originally Posted by Easy peasy View Post
    I see you are switching on & off quite slowly with those high-ish gate resistors
    Yes, this is the gate signal

    Click image for larger version. 

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    The plateaus disappear if I turn off V1 and V2, what could cause that?

    Quote Originally Posted by Easy peasy View Post
    I - but you still need 1uF 630V say across the pair of IGBT's from top collector to bottom emitter to soak up the turn off wiring inductance energy
    I tried with a 0.1uF (didn't have 1uF) and the only thing it seems to do is to distort the positive cycle.

    Click image for larger version. 

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    Note: 1000x probe


    Quote Originally Posted by Easy peasy View Post
    I zoom right in on those over shoots for a good look ( 500nS/div & 100nS/div ) it may be just CM pickup ... how many amps are you trying to switch ?
    Like this?
    Click image for larger version. 

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    Note: 1000x probe

    Quote Originally Posted by Easy peasy View Post
    how many amps are you trying to switch ?
    At the moment around 3-400mA

    Quote Originally Posted by Easy peasy View Post
    I - without seeing the entire schematic and a picture of the hardware - it is hard to make positive suggestions ...
    I know, but it's too ugly to show to other people. And I'm not asking for miracles, just a few hints and pointers from experienced people would be appreciated.

    - - - Updated - - -

    Quote Originally Posted by barry View Post
    No decoupling caps and no PCB, and you're wondering why your circuit works like crap???
    I'm sorry about that, but it's my first attempt at an IGBT application, and I didn't have anyone else to ask before posting.

    Quote Originally Posted by barry View Post
    You probably have a LOT of stray inductance, not to mention inductance from the ground probe of your oscilloscope.
    You are probably right about that.



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    Re: Serious IGBT overshoot

    Hi,

    The plateaus disappear if I turn off V1 and V2, what could cause that?
    I recommend to read some MOSFET or IGBT driving tutorials.

    The plateau should be well explained in every good tutorial.

    Klaus
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    Re: Serious IGBT overshoot

    Quote Originally Posted by KlausST View Post
    Hi,


    I recommend to read some MOSFET or IGBT driving tutorials.

    The plateau should be well explained in every good tutorial.

    Klaus
    Hi Klaus.

    Yes good idea, I read this one from Infenion which is quite comprehensive, but no discussion about the plateaus though.



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  11. #11
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    Re: Serious IGBT overshoot

    Hi,

    Your document is about snubbers, whuch ar connected at the output of a Mosfet / IGBT.
    But I recommended a "driving" tutorial, which is at the input, the gate.

    The plateau is called "miller plateau". Do an internet search, you will find a lot of informations.

    Klaus
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  12. #12
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    Re: Serious IGBT overshoot

    Your gate drive is possibly too soft, the overshoot is well reduced with the 100nF 630V cap across the supply right by the IGBT's the distortion tells me your 200V supplies are very soft ( the top one any way ) - at least you won't cook your devices at 400mA ( unless they have no heatsinking )

    try 1uF 630 V and all your overshoot may disappear ... ( 2 x 2u2 400V in series or similar ... )



  13. #13
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    Re: Serious IGBT overshoot

    you haven't zoomed in on the overshoot at turn off - what you have captured is a blip ... please try again ...



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