OLTC (was Fwd: Hmmm...)

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

Original poster: "mrpaslow by way of Terry Fritz <twftesla-at-qwest-dot-net>" <misterpaslow-at-yahoo-dot-com>

Hi Terry,
Here's more from Brian.
Dan Kline

> Subject: Geez...
> Date: Sat, 17 Aug 2002 01:47:16 -0400
> 
> Hey,
> 
> I am a dope. Since it was 3AM I neglected to do any
> math on Terry's power supply. I was only referring
> to the first stage of the setup, where he charges up
> the 47uF cap. Even though he may not get 1300V on
> the 47uF cap, If he opens the IGBT while the 150mH
> coil is charging, the inductor becomes the source,
> and its polarity reverses. This will place a greatly
> negative potential on the end of the coil connected
> to the IGBT, so that the total voltage across the
> IGBT consists of DCin - Vc + V(150mH). It is the
> voltage kick from interrupting the coil that is the
> problem, which works out to overvoltage the IGBT
> unless you provide an alternate current path for the
> kick pulse. Hence the afforementioned diode of my
> last post...
> 
> Depending on the type of IGBT you have, it may have
> some built in body diodes which will clamp a few
> millijoules of inductive energy before overheating
> the die. It's OK for an occasional surge, but not
> for repetitive abuse.
> 
> For some reason I cannot get a clear pic of the
> schematic, so I am working a bit in the dark. Is the
> IGBT in the first section ONLY used to turn on the
> supply, then stays on until the ozone fills the room
> and it is time to go out for a cig? If it is only an
> on switch, then why not just use a triac on the AC
> input side of the bridge? Is is a lot less to worry
> about just to turn the thing on (but it must stay on
> until the 60HZ half cycle is complete). There are
> also optoisolators with small triacs that can be
> used to trigger the larger power triac (the ON
> switch).
> 
> Or, is the supply turned on just long enough to
> charge the 47uF cap, then the supply is turned off,
> then the 47uF cap is discharged into the primary of
> the output coil, then the cycle repeats again by
> turning on the supply to again charge the 47uF cap?
> If this is the duty, I can see why you would want an
> IGBT for the power switch.
> 
> This is a very novel idea which I would like to
> learn more about. Has someone posted an article on
> the operational theory behind this setup? I am
> throwing out a lot of guesses and think it's time
> for me to hush until I learn more. :)
> 
> -Brian
> 
>