Re: Solid-State Marx (fwd)

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Original poster: <sroys@xxxxxxxxxxxxxxxxx>



---------- Forwarded message ----------
Date: Mon, 18 Jul 2005 01:54:47 +0800
From: Peter Terren <pterren@xxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Solid-State Marx (fwd)

I recently made a solid state Marx out of 3 x 250V SIDAC's, 4 photoflash 
caps and 12k resistors run from 300VDC.

It wasn't that successful.  At this low voltage of about 1kV, I was not 
after sparks but preferred to charge a capacitor to give a more constant DC 
output. Normally the load is a spark gap which fires then disconnects itself 
and presents no load until the voltage rises high enough again. 
Unfortunately, using a simple resistor load to discharge the Marx capacitors 
fully and rapidly and yet still present a high enough off-state resistance, 
seemed incompatible.  I also need the resistive load to limit the peak SIDAC 
current to 1A RMS or 100A for very brief peaks.
It did fire as expected but to turn off the SIDAC's I had to cut the input 
supply briefly.

You may want to think about what you will do with the output before you 
spend a lot of time designing the supply.

Peter

----- Original Message ----- 
From: "High Voltage list" <hvlist@xxxxxxxxxx>
To: "hvlist" <hvlist@xxxxxxxxxxxxxxxxx>
Sent: Friday, July 15, 2005 10:55 PM
Subject: Solid-State Marx (fwd)


> Original poster: <sroys@xxxxxxxxxxxxxxxxx>
>
>
>
> ---------- Forwarded message ----------
> Date: Fri, 15 Jul 2005 13:17:13 +0930
> From: Matthew Smith <matt@xxxxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: Solid-State Marx
>
> Hi All
>
> This idea started off as something driven by the flash unit from a
> disposable camera until I realised that I'd forgotten about driving the
> MOSFET gates!
>
> Here's the schematic:
> <http://www.mss.cx/img/ssmarx1_sch.png>  (image 917x348px, 5.8kbytes)
>
> I have a rail of spare MOSFETs that can be used in this design:
> PHP6N60E; Vdss=600V, Id=5.4A, Rds[on] < 1.8 Ohms
>
> Capacitors are photoflash types from disposable cameras.
>
> Assume that the input voltage to the circuit is about 250V.
>
> What would be the best way to achieve switching of the charging
> transistors?  Put gate windings on the step-up transformer for
> synchronous rectification (lose the diode)?
>
> (I'm going to worry about the discharge part once I've got the charging
> sorted.)
>
> Cheers
>
> M
>
> -- 
> Matthew Smith
> South Australia
> http://www.kbc.net.au
>
>
>
>