RE: Triggering Stacked IGBTs

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "S&JY" <youngs@xxxxxxxxx>

Sorry - I just assumed that since this is a TC list, all would assume the
load would be a TC primary.  The idea is to substitute a triggered IGBT
stack for an ARSG in a standard resonant DC supply TC topology.  In my case,
a primary MMC of 50 nF and resonant frequency of around 85 kHz.

Yes, the idea of having a string of SIDACs to independently fire the stack
of IGBTs in case the supply voltage is cranked up too high is a great idea -
sort of a high voltage crowbar.

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: Saturday, February 17, 2007 5:27 PM
To: tesla@xxxxxxxxxx
Subject: Re: Triggering Stacked IGBTs

Original poster: "Steve Ward" <steve.ward@xxxxxxxxx>

Steve,

What is the nature of the load?  I was recently thinking of such an
IGBT array, but the load was a parallel tuned LC (like a VTTC primary
circuit, replace the tube with IGBT array).  In this case, the dv/dt
upon turn off is relatively small, because you basically have to
charge up the cap across the primary.  This of course allows much more
slack in the IGBT drive timing.

It may be possible to simply use a SISG array along with pulse
transformers (which are easy to isolate to many kV).  This would
normally use the pulse transformer to turn on the switch, but if
something went wrong, the sidacs should kick the IGBTs on.

Anyway, the design constraints are gonna depend a lot on what your
load is going to be.  Unfortunately, i dont yet have experience in the
"seriesed switch arrays" yet.  Havent really needed them.  Though i
did build a marx-like inverter that produced around 1600V from a
400VDC input at 150khz (not sure if this is of any use to you).

Steve Ward

On 2/16/07, Tesla list <tesla@xxxxxxxxxx> wrote:
>Original poster: "S&JY" <youngs@xxxxxxxxx>
>
>
>I am looking for ideas on practical and not overly expensive ways to
>trigger a stack of IGBTs.  For example 10 1,200 volt IGBTs in series
>to take the place of a spark gap.
>
>The SISG (SIDACs) scheme is good, but I want more control.  I would
>like to be able to externally vary pulse rep rate, pulse width and
>the DC voltage to the stack independently.  I suppose I am after a
>poor-man's variant of a klystron modulator such as used in particle
>accelerators.
>
>One method is to use fiber optic coupling to photo detectors
>controlling each IGBT.  I have read these are susceptible to
>electrical noise.  Other methods use pulse transformers, e.g.
>modulated several mHz inputs and rectify the outputs to control the
>gate.  Or use pairs of pulse transformers to trigger a flip flop on
>and off to control the IGBT gate.  Of course, whatever scheme is used
>must trigger all the gates simultaneously.  And the trigger circuits
>on the IGBT side must derive their power from the main DC power to
>the IGBT stack (to avoid the need for isolated power supplies).
>
>Can some of you steer me to a source of ideas?  Better yet, can any
>of you report your practical experience triggering series connected IGBTs?
>
>Thanks,
>
>--Steve Y.
>
>
>
>
>






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