Re: phasing GDTs with MOSFETS

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

Original poster: Jan Wagner <jwagner-at-cc.hut.fi> 


On Wed, 28 Apr 2004, Tesla list wrote:
 > Original poster: Fucian-at-aol-dot-com
 > Is there a way to do this with just one channel?I have a 2 channel scope
 > but just one probe...BTW-scope wroks good!
 >
 > Also, did i measure my GDT right?I did this:
 >
 > I connected the primary to the driver and then took the probe ground and
 > clipped it to circuit ground, not the output, then i probed one of the
 > secondary output pins(commercial GDT) I got a decent square wave with a WEE
 > bit of noise on the wave...

For only a few 10-100kHz you can just stick a wire into the BNC
connector, and a second wire to the scope GND connector or BNC outer
jacket.

You could also connect one end of the primary to ground, the other to your
test signal (via a series capacitor). Select one secondary, ground one
end, put your probe ground clip on the other end (and a resistor or small
<5nF capacitor to ground), and place the probe signal tip on the primary
where the test signal goes in.

If the waveform you see is small in amplitude, this secondary has
the same phase as the primary. If the signal is large, pri and this sec
are 180deg shifted - with that _exact_ configuration of the two selected
wires being GND/signal return, and the other two signal input or output.
Which means it's best to stick those descriptive labels on the wires
_before_ you go changing anything :-))

(now, actually, you could figure out the exactly same thing just by
looking at which direction the secondary is wound, vs the winding
direction of the primary, AND, what primary end you select as signal
input and which as signal return. But sometimes it's less confusing to
just go and measure it, instead of breaking your brains on it :o))

cheers,
  - Jan

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