Re: [TCML] IGBT paralleling

[DC Cox <resonance@xxxxxxxxxxxx>]

There still seems to be confusion here.

In summary, I'm saying that operating a 1200 or 2400 Volt IGBT on say a line
doubled 635 VDC is a waste of money and "headroom"  --- the differential
between 2400 VDC and 635 VDC.

I trust this will clear the qir.

Dr. Resonance





On Mon, Jul 12, 2010 at 4:28 PM, Brian <brianv@xxxxxxxx> wrote:

>  Dave,
>  That is what I meant, and did say stay under the spec max ratings and it
> should work. Even running them over the max spec on short duty cycles can
> be
> ok. I am not sure where this Headroom thing came from and how it got
> decided
> that needs to be filled because it don't. But Like I said I might have
> missed something somewhere. The Handling voltage I was talking about was
> nothing more than Max rated voltage of the device and nothing more, what
> ever the absolute MAX is on the spec that is what I was talking about.
> Sorry
> for the confusion.
>
> Brian
>
> I'mve no idea what a 'handling voltage' spec is.
> In my training there is max voltage, or standoff voltage.
> or withstand voltage spec.  This is the voltage the
> device is specced to NOT breakdown under, when 'off',
> (The actual voltage for any given specimen will be higher,
>  a bit, but don't plan on it....).  This means that same
>  spec is more or less the max the device will 'handle' in
>  ESD as it is 'handled' during assembly, etc.
>
> I can think of no reason why the applied voltage
> 'needs' to 'fill' this rating: the device should be
> quite happy anywhere under the rating.  BUT: Higher
> ratings cost more dollars (euro's, whatever...).  In that
> sense of the full voltage rating is not being 'used'
> then money is being wasted.  Or.  The resulting design
> is more rugged/reliable.  Its a design tradeoff...
>
> One thing I've not seen mentioned (did I miss it?):
>
> Paralleling 'things', especially active devices, can be
>  tricky.  Most notably, the devices may not QUITE match:
>   'identical parts aren't': Frumps law of design...
>
> Paralleling power devices can result in Not Equal 'sharing'
> of currents.  Either forced sharing, or conscious
> allowance is in order...
>  best
> New dwp:     dave_p@xxxxxxxxxxx
>
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