Re: Long Pulse IGBT GDT design / HV-OLTC

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

Original poster: sparktron01-at-comcast-dot-net 

Hi Jim

Optocouplers are available to 3.75kV isolation (Toshiba TLP250 / TLP351 
family).
However to make work on a series switch requires an isolated current loop drive
for each level of the switch for isolated +/- DC power for the optocoupler 
driver.  Then you still need a fiber-optic link bewteen your  main pulse 
generator and each level of the switch.  I've seriously looked at the 
Toshiba OC approach, and the part count, isolated DC power supply 
availability (and cost) and circuit synchronization issues make that 
approach quite unreasonable, at least for "us guys"...  :^D

The AN950 International Rectifier approach as mentioned by Jan appears to 
be, at least on the surface, a much more reasonable and maybe reliable 
alternative.

I'm feasibility testing at this point, but at least I see a vision where I 
want to go...
the HV-OLTC based on a series stack IGBT switch.  2.4kV PT powered by an 
IGBT AC chopper (pulse by pulse current limiting) into a resonant charging 
stage as previously used by other experimenters (notably Steve Conner among 
others).  8 series switch sections with Vbalancing circuit and TVS 
protection using 1.2kV IGBT's
powered at a peak charging voltage of 6.8kV; shooting for a HONEST 1.0MW 
ring wave power (4.0MW peak [6.8kV * Ipeak ring wave] ). He.., I'm using 
samples at this point, and have 20 more coming, might as well enjoy the 
sparks (and IGBT detonations)...   :^)

But first steps will involve building a prototype pulse generator 
controller and SSVariac, and 1.2kV level switch running at 1.0kV, and take 
it to detonation to determine maximum Ipk my devices can tolerate, what 
drive levels are needed for optimal performance, and GDT / gate drive 
design.  I have some new IXYS gate drivers that can sink or source up to 
30A pulse (8A DC continuous) that will be used for switch triggering 
loop.  The point is the hardware and published technology (circuits and 
validation of dynamic balancing) has recently become available; so there is 
at least a glimmer of hope of making this concept work...

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA
-------------- Original message --------------

 > Original poster: "Jim Mitchell"
 >
 > Perhaps some optocouplers?
 >
 >
 >
 > On Sat, 09 Oct 2004 11:39:06 -0600, Tesla list wrote:
 > > Original poster: sparktron01-at-comcast-dot-net
 > >
 > > All
 > >
 > > Need some design guidance for a GDT for an IGBT power switch. Need to 
turn
 > > on for ~300usecs, off time of 1.5millisecs (PRF = 400Hz). If drive 
voltage
 > > is 30Vpk to pk, results in a V*t product of 9000V-usecs (typical GDT
 > > product is in
 > > 200-500V-usecs).
 > >
 > > Transformer may saturate, but will DC restore during off time so not
 > > particularly
 > > a big deal. Any design guidance out there for DC restoration using
 > > standard toroids for long pulse IGBT gate drive?
 > >
 > > Thanks!
 > >
 > > Best Regards
 > > Dave Sharpe, TCBOR/HEAS
 > > Chesterfield, VA. USA
 > >
 > >
 >
 >
 > --
 > Regards - Jim Mitchell
 >
 >