Re: [TCML] SISG Technology

[Bert Hickman <bert.hickman@xxxxxxxxxx>]

Hi Jim,

Commonly available thyristors would perform poorly as the high current 
switching elements in a TC primary circuit. Unless specially fabricated 
for pulsed power use, they'll turn on too slowly (i.e., specifically the 
di/dt spec). This may progressively or immediately destroy the thyristor 
as excessive current flows through a small conducting region before the 
rest of the device can turn on. This problem occurs via normal gate 
triggering, by forced turn-on through device overvolting, or via rapid 
voltage changes (dv/dt) across an "off" device. All can occur within a 
Tesla Coil primary circuit. Using small HV thyristors (i.e., SIDAC's) to 
trigger readily available IGBT's is a more cost-effective approach, and 
is scalable to a wide variety of high current IGBT's. Indirect optical 
trigger control through fiber is already used on many DRSTTC's.

Bert

Jim Mora wrote:
> Hello Bert, et al,
>
> I wonder if anyone on the list has experimented with this approach. My first
> impression is that component costs would be higher? Triggering with fiber is
> interesting...Thoughts?
>
> Jim Mora
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of Bert Hickman
> Sent: Thursday, February 05, 2009 6:54 AM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] SISG Technology
>
> Hi Bart,
>
> Nope - this guy didn't abscond with Terry's SISG design...
>
> This particular patent (dated 2002) predates Terry's SISG work by about 
> 4 years and, unlike Terry's approach it uses stacked high speed 
> thyristors as the main current carrying element, with optical 
> sensor/IGBT or pulse transformer triggering for each stage. The SISG is 
> kind of the reverse of this - it uses a thyristor to trigger IGBT power 
> switches. This proposal appears to be a pulsed power adaption of similar 
> optically or transformer isolated stacked thyristor circuits used for 
> the inverters in HVDC electrical power transmission systems. Specially 
> fabricated high di/dt thyristors were employed in this application for 
> faster turn on time. As with the SISG, diodes are used to conduct 
> reverse pulse current. You can see the full disclosure of the approach, 
> schematics, and test results here:
>
> http://www.wipo.int/pctdb/images4/PATENTSCOPE/17/70/e9/0070e9.pdf
>
> HOWEVER: I see no reason why stacked SISG-like circuits could not be 
> used for certain pulsed power applications, and it would not surprise me 
> to see SISG-like circuits applied to this arena...
>
> Bert




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