Re: SSTC idea - DRSSTC ?

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

Original poster: "jimmy hynes by way of Terry Fritz <teslalist-at-qwest-dot-net>" <chunkyboy86-at-yahoo-dot-com>


Hi Stephen,

In order to use one transformer for the whole bridge, I would have to add 
resistance to damp out the ringing, to prevent the IGBTs from turning on 
early.  I dont know how much resistance would be needed to keep the gate 
from turning on, but it might be reletively big. I would look into it if I 
didnt already have a solution.  The DC blocking capacitor is just one of 
those "good practice" things and not needed if the mean voltage is zero, 
right?

I want to keep with the microcontrollers because it is easier to do PLL. I 
dont want my IGBTs trying to turn off at several hundred amps each cycle. 
The micro also allows me to do cool stuff like sweep the break rate, play 
songs (low fidelity) and do double bursts easily. To do double bursts I 
would have to switch phase right after the first burst, which could be 
challenging w/out a microcontroller. I could also do several bursts in a 
row followed by a break, like staccato SSTCs and VTTCs. Didn't you mention 
that you were thinking about doing that with your cool little OLTC?

  Tesla list <tesla-at-pupman-dot-com> wrote:
Original poster: "Stephen Conner by way of Terry Fritz "

At 18:06 31/03/03 -0700, you wrote:
 >Original poster: "jimmy hynes by way of Terry Fritz "
 >
 >
 >
 >Hello Jan,
 >
 >Thanks for the comments, I've been thinking along the same lines.
 >
 >Earlier, I tried using one driver chip per transformer with a capacitor do
 >remove the DC bias

As far as I know, you only need one gate drive transformer for your entire
H-bridge, even if you're using dead time. If you allow the gates to be
driven with +/- 30V or whatever, then the input waveform to the GDT will be
symmetrical. You use a full-bridge (two driver chips) to drive the GDT, and
during the deadtimes you set both arms of the bridge to the same state,
thus imposing ze! ro voltage across the GDT and turning all the IGBTs off.
You still use a DC blocking capacitor, but the mean voltage across it is
zero so you don't have to worry about transient stuff.

A commercial controller chip like the TL494, or its more popular relative
the 3525 (widely second-sourced, can be UC3525, KA3525, LM3525, SG3525,
etc) would take care of all the deadtime/drive signal generation stuff for
you (See TL494 Feedback SSTC schemos on www.hvguy-dot-com for inspiration) then
you could use a 555 timer to set the burst length, and you wouldn't have to
worry about trashing any more microcontrollers ;)

Steve C.





Jimmy