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Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
You know I still use good old CAT5 on my GDTs. I have found over the years that nothing really beats it from a leakage inductance stand point. Those pre-twisted pars are great for GDT drive. Usually I will drive all the stripped windings in parallel while using the solids as my secondaries, this gets you a primary that's twisted with each individual secondary.
As other have said stay away from magnet wire with GDTs, remember that your GDT needs to able effectively isolate your bus voltage because when you turn on a high side and low side switch two of your winding will have the full bus voltage between them. Magnet wire is usually only good for a couple hundred volts of isolation and your bridge can be on the order of 350VDC or 650VDC in most cases. Magnet wire also doesn't like making 90* turn as it has to do around the core of a GDT. This can lead to breaking in your insulation and possibly crow-baring your gate with the full buss voltage.
Don't get to tied up in the shape and look of your waveform. What matters at the end of the day is how fast and effectively it turns on the gate.
Here are my suggestions:
1. For starters be sure to test your GDTs while actually connected to a gate. The type of load on the GDT will drastically effect the wave-shape. From your scope shots it doesn't look like your are driving a gate. Overshoot and rise time tend to improve with a load on the output.
2. I would select a different core, although N30 core has an initial permeability of 4300u it's saturating flux density is kinda low (0.38T) Check out T65 (0.46T) or some of the other flavors from TDK.
Registered Member #46164
Joined: Wed May 07 2014, 08:16AM
Location: California, USA
Posts: 89
Surely twisted magnet wire has a lower leakage inductance, than cat5 cable. Magnet wire can have a very high breakdown voltage depending on the grade. I think the mechanical strain failure mode is an issue though.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Halfdead wrote ...
Surely twisted magnet wire has a lower leakage inductance, than cat5 cable. Magnet wire can have a very high breakdown voltage depending on the grade. I think the mechanical strain failure mode is an issue though.
The different in leakage inductance is marginal. Although you may be able to achieve a couple 10's of nH less leakage inductance with magnet wire it's not worth the large increase in probability of failure. This amount of leakage is really not going to show much improvement in the waveshape.
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GDT wire
