RE: DRSSTC -- EMI scope problems

["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>

I need help with a solder joint now... ;-)

The Voltage on the IGBTs was from the collector of the
top IGBT to the emitter of the lower one. It was the +
and - supply voltage. I think it is fake too. I put a
20 volt zener in there to clamp it, but it didn't
clamp the ringing, so it must not be real.

At this point I think I am going to get ready to add
the secondary, and start turning the variac knob.
Maybe I will prepare some more graves in the silicon
graveyard ;-)

--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "Stephen Conner by way of Terry
 > Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>
 >
 > OK... First of all, I ought to say, this is becoming
 > more of an electonic
 > debugging session than a discussion on Tesla coils.
 > Maybe Terry would
 > prefer if we carried this on by email off-list?*
 >
 > *<if it may be a future interest or something to
 > those that follow your
 > efforts it is fine.  If it gets into like a solder
 > joint or something
 > really basic, then maybe direct e-mails to solve the
 > specific issue would
 > be best - T>
 >
 >
 >   I now get to look at the microprocessor level. It
 > has
 > >absolutely no 60khz on it, but has high frequency
 > >"chirps" at every half cycle, adding a choke had
 > >absolutly no effect on it.
 >
 > I would suspect either feedthrough of the micro's
 > clock frequency (probably
 > OK)... or your gate driver chips have parasitic
 > oscillations... prepare
 > another plot in the Silicon Cemetery 8--at-
 >
 >
 > >The voltage across the IGBT brick may be a problem
 > >though. It looks like a 60 khz sinewave that goes
 > from
 > >0 to twice the normal voltage.
 >
 > Do you mean the gate voltage or the collector
 > voltage? I would expect to
 > see 60kHz _square_ waves in both of those places.
 > And why twice the
 > voltage? The co-pack diode of the upper IGBT (I
 > assume you're running a
 > half or full bridge) should clamp it at the rail.
 >
 >
 > >it takes a three foot diameter turn to get
 > >enough inductance. There is no way I have that much
 > >area
 >
 > One possibility is that the leakage inductance of
 > your gate drive
 > transformer could be resonating with, or forming a
 > low-pass filter with,
 > the gate capacitance of the IGBTs. This would tend
 > to turn the square wave
 > drive into a sine wave. Hence the collector voltage
 > might end up kind of
 > sine wavey too. The gate capacitance is big, and
 > Miller effect makes it
 > look even bigger, so the GDT design is a pretty
 > tough challenge... one that
 > I went to great lengths to avoid :)
 >
 > Or of course it could be interference caused by a
 > ground loop picking up
 > the primary current. The actual voltages on the coil
 > might be clean. THe
 > way to test this is to remove the probe tip from the
 > circuit and touch it
 > to the probe's ground lead (which you leave
 > connected to circuit ground)
 > Any signal that you can still see is ground loop
 > interference.
 >
 > Steve C.
 >
 >
 >
 >


=====
Jimmy