[TCML] Spark gap / SCR simulation problem

["Chris Swinson" <list@xxxxxxxxxxxxxxxxxxxxxxxxx>]

Hi all,

After running some spark gap simulations ( just pondering with peak currents 
more than anything) , for my spark gap simulation (a switch with 1mR losses) 
I get around 300 peak amps... now with the exact circuit but with a SCR I 
only get 6 amps peak current...

Now with the SCR being only a single diode, I expected it not to work as the 
voltage could only ring in one direct, however, the simulation actually 
works twice as good with only the SCR in place (no anti-parallel diode)

Now, should the primary ring with only the SCR in place  and no 
anti-parallel diode, or is my simulation broke ?

and second, why such a drop from 300amps to 6amps ?... I can only assume the 
SCR DV/DIDT ratings are letting it down ?

If anyone has a spice model for a good SCR can someone send me one off 
list... The one I am using I just used the best SCR I could find and just 
altered the voltage rating to 20KV... though I have no idea about all the 
other figures in the file...

The SCR data I have is..

**********
*SYM=SCR
*SRC=SCR_CHRIS;SCR_CHRIS;SCRs;TECCOR; 200000V 50000A
.SUBCKT SCR_CHRIS   1 2 3
*    TERMINALS:  A G K
QP  6 4 1  POUT OFF
QN  4 6 5  NOUT OFF
RF  6 4    80MEG
RR  1 4    53.3MEG
RGK 6 5    14.1
RG  2 6    1.85
RK  3 5    1.5M
DF  6 4    ZF
DR  1 4    ZR
DGK 6 5    ZGK
.MODEL ZF   D (IS=28F IBV=2U BV=200000)
.MODEL ZR   D (IS=28F IBV=2U BV=200000)
.MODEL ZGK  D (IS=28F IBV=2U BV=5)
.MODEL POUT PNP (IS=28P BF=1 CJE=143P TF=59.5U)
.MODEL NOUT NPN (IS=28P BF=100 RC=6M CJE=715P CJC=143P TF=4.25U)
.ENDS
**********


I am pretty sure it is the SCR ratings to blame... I also invented a "Chris 
diode" and used 2 anti-parallel in series with my spark gap switch and that 
works fine... with a single diode I only get a single pulse and no ring 
down.. so again looks like there is something odd with my SCR simulation... 
this must be the same reason why a anti-parallel diode upsets it further...

Another interesting thing, the diodes in series with the spark gap rings 
down in 600uS, the spark gap on its own takes 10mS with 1mR loss.  with 20mR 
loss it equals my diode, so it would appear the diodes are acting as a 20mR 
resistance for some reason also.

Chris

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