Re: IGBT Brick hits 1200A

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 13:30 18/05/03 -0600, you wrote:
>Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><dhmccauley-at-spacecatlighting-dot-com>
>
>Sounds like you need a simple snubber (resistor-capacitor) across the diode
>to supress the ringing.
>I have some detailed MathCad/Pspice calculators / simulations for precise
>snubber design if you are interested.

In the last OLTC I built, I used some transzorbs (TVSs) in series to a 
total of 800V. But it functioned fine without them. The drive circuit was 
designed to only turn the IGBTs off at times when the current was reversed. 
In this way the IGBT would actually see soft turn-off on the next 
half-cycle. The snubbers were really just there as a backup if the drive 
circuit malfunctioned.

The circuit I'm working on just now is so big that I doubt any kind of 
snubber could save the IGBTs if they were accidentally turned off during a 
positive current peak. Except possibly for some giant MOVs or transzorbs, 
but I have never seen any big enough. I believe that the ringing I'm seeing 
just now is totally harmless.

Steve C.