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Serious IGBT overshoot

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Swend

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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?

schemeit-project(1).png

SDS00035.PNG

Regards Svend.
 

Where are your decoupling caps?

Where is your waveform from?

Where is your PCB layout?

Where is your overshoot?

What are your driving signals?
 

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 barry

Where are your decoupling caps?

I don't have any yet

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

Where is your PCB layout?

I don't have any, it's a bird nest, no breadboard, only soldering.

Where is your overshoot?

I don't know if I used the correct technical term, so I have marked it in red.

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.

schemeit-project(2).png

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

SDS00036.PNG
 

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
 

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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    Swend

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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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    Swend

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Hi Easy peasy!

I see you are switching on & off quite slowly with those high-ish gate resistors

Yes, this is the gate signal

SDS00040.PNG

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

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.

SDS00038.PNG
Note: 1000x probe


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?
SDS00037.PNG
Note: 1000x probe

how many amps are you trying to switch ?

At the moment around 3-400mA

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 - - -

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.

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.
 

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
 

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
 

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 ... )
 

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

Where are your decoupling caps?

I've been searching for decoupling caps for IGBT like 1 hour a day like 2-3 days. I checked many tutorials, datasheets and application notes. I haven't seen any decoupling capacitors.

What is the "decoupling capacitor" in IGBT commutating / driving ? Do you mean to putting a capacitor between collector and base ? Collector and Emitter ? Base and Emitter ? For what purpose ?

I'm on designing switching layer and I need urgent reply.
 

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
That's basically putting a capacitor at source.
soak up the turn off wiring inductance energy
Do you mean there will be an energy stored in PCB because of an stray inductance and bypass it via that capacitor ? What if the input is AC not DC ?

- - - Updated - - -

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

I searched many manufacturer IGBT tutorials, application notes, datasheets, datasheet tutorials, miller plateau voltage papers and now I'm confused like a cat watching pinball game. Could you please point out a spesific tutorial so I can print out and read line by line.

Thanks..
 

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