Re: Recent s.s.t.c work

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Ken,

At 04:34 PM 10/15/2005, you wrote:
> Take a look at
> http://www.hot-streamer.com/temp/KCH_TCH5.jpg
>  and
> http://www.hot-streamer.com/temp/KCH_TCH5A.jpg
> "5" is a new photo like the "4" I previously posted while "5A" is 
> waveforms from a simulation I just ran of a basic IGBT H-bridge 
> driving the 15 uH/400 nF load that I have in the hardware.  In 5, 
> the top waveform represents primary current in my hardware & the 
> bottom represents the H-bridge's power-supply current.  In 5A, the 
> green waveform represents the load (i.e. primary) current & the blue 
> waveform represents the supply current.
>
> Hardware & simulation show essentially the same waveforms

Always a "good" thing :-)))

> , except, in the hardware, for a) the fuzz at switching-times,

Probably due to "tiny" inductances ringing up with capacitances.  Not 
a big deal unless they get really big.  Many bypass caps and even 
ferrites can fix it if needed.  Over time, with big "short" busses 
and many big low-Z bypass caps, mine have sort of vanished.  But you 
can still see ringing for sure!!

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-15-002.gif

If your scope or probe has a bandwidth limit button on it, just push 
it, and be happy :o))

> b) an offset from the zero line

You should track that one down for sure!  Could be a bad FET or 
something.  Could be just a scope probe offset too...  But IMHO DC 
offsets need to be figured out for sure!!  If your scope is on AC 
coupling, it might be the coupling cap in the scope charging...  It 
is probably a silly thing like that.

However, I did have a big DC offset on a number of occasions in life 
and when the circuit was put under full power it blew the crap out of 
everything!!

>  and c) the "squiggle" in the power-supply current about 1 us after 
> the switching times.
>
> Interesting...what's the squiggle, I wonder?

Could it be not enough super low resistance bypass caps.  Here is my 
circuit when I took out the poly bypass caps but had 20 x 22uF HF 
electrolytics in line (ignore the white in the background):

http://hot-streamer.com/temp/OL-DRSSTC-2005-10-14-002.gif

The blue line is the buss voltage...  =:O    Now THAT is a squiggle!!!

Cheers,

        Terry


> KCH