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Bridge design?

Thread starter #1
So I have a fairly decent understanding of how my UD2.7 driver works but what I'm struggling with is bridge design.
I have a CM200DU-24F on the way as well as a couple of TO-247 full bridge boards that I need to populate but as far as the actually nitty gritty of these go, I'm totally in the dark.
Ideally, my coil will be running the CM200 and I'll probably end up using the full bridge boards for other projects but can anyone help me out with schematics, tips, advice and information on how to turn my CM200 into something usable for my coil?
I'm in the dark as to where to go once the signal leaves my controller.
I'm on 240V mains here so there's no need for any voltage doublers, I just need a basic, strong and reliable power delivery system.
Thanks in advance.
 

DerStrom8

Super Moderator
Most Helpful Member
#2
Hi there,

Perhaps this document will help. It is basically a translation of my blog posts on my coil here at ETO to a PDF:

https://teslaunderground.com/Matt/VermonsterMiniBuild.pdf

Pages 17 and 26-28 explain the operation of the H-bridge, as well as showing a generic schematic diagram. Feel free to ask if you have specific questions about the document - I'd be happy to answer them :)

Regards,
Matt
 
Thread starter #3
So I'll be working off this for my brick bridge and I have a few questions.
C4 and C7 - What voltage rating am I looking at for these caps?
C1 and C2 - I have a pair of 450V, 2400 uF caps, are these overkill?
With R1 and R2, am I best off scoping the output of my GDT and see which resistor gives me minimal ringing?
C6 - I have a CD 940C 20w1k PP cap (1uF 2000VDC). Is this suitable?

http://kaizerpowerelectronics.dk/wp..._-_kaizer_drsstc_ii/kaizer_drsstc2_bridge.jpg
 

DerStrom8

Super Moderator
Most Helpful Member
#4
C4 and C7 - What voltage rating am I looking at for these caps?
Since you'll be powering your coil from 240VAC, your bus voltage will be around 340VDC. I wouldn't trust caps with ratings lower than 400VDC, and I would personally shoot for at least 450 or 500 VDC.
C1 and C2 - I have a pair of 450V, 2400 uF caps, are these overkill?
There's not really an "overkill" for DRSSTC bus capacitors. Larger caps will give you better smoothing of the rectified AC input, and will be able to supply significantly more current to the resonant circuit. You may not need both for a coil your size, but it certainly couldn't hurt.
With R1 and R2, am I best off scoping the output of my GDT and see which resistor gives me minimal ringing?
That is exactly how you do it. In fact, Richie Burnett has a webpage explaining how to adjust the GDTs and gate resistors based on different waveforms you get. This page was immensely helpful to me:

http://www.richieburnett.co.uk/temp/gdt/gdt2.html

Obviously don't do your probing while the high voltage DC bus is powered, but do make sure your IGBTs are connected (of course).
C6 - I have a CD 940C 20w1k PP cap (1uF 2000VDC). Is this suitable?
That will probably work ok.
 

DerStrom8

Super Moderator
Most Helpful Member
#6
Which cores did you end up buying?
 

DerStrom8

Super Moderator
Most Helpful Member
#8
Oh boy, I hate to break it to you but those may not work very well for you. The N30 material has a permeance (Al) of around 5700nH. For gate drive transformers you really need to be around 10,000nH or higher. Instead I'd recommend the T38 material (Al ~ 13,500nH). The corresponding part number from EPCOS is B64290L0674X038, which happens to be the exact core I used for my GDTs on my DRSSTC.

The problem with a low permeance in gate drive transformers is that it is more difficult for the primary coil to generate a magnetic field in the core. This leads to signal degradation on the secondary coils. In order for strong, precise translation of drive signal to IGBT gate signals your permeance needs to be quite high.

Is it too late to swap out your order?
 

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