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Batch of TO- device bridge PCBs made (and new coil photos)

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Dylan

Sun Sept 07 2008, 12:52AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Hi all,
I just went a bit silly and had a large batch of bridge PCBs made up, below are some photos , but in sumary there are two different boards for either opposing or matching device layout.
I designed the matching layout one so as to fit the whole bridge onto an intel socket 478 heatsink.
The opposing layout one for seperate or larger heatsinks, and easier device replacement.
There are plenty of holes ( all a little oversized again for easy desoldering) for mounting various configurations of bridge components.
They are also good for half bridges as you simply replace the output devices on one side with your half bridge caps.
I will be listing these on ebay shortly, once I get my act together and stop playing with them myself

.
Anyway the photos:

Opposing layout type on two intel cpu heatsinks.
This is for my new experiment in seeing how far I can push a batch of TO247 devices I just got (HGTG12N60A4D).
So everything is designed to come apart easily for device replacement

Ive got the power connections on one side and the gate drive on the other:
All unused holes are plugged, I figured it would help with current carrying capacity.
2832041618 B44e51e15e

Turns out the heatsink clip is a perfect fit to hold the GDT

, it just clips on the corners of the board.
2832299820 538e0f69a6

Fuzzy cam view closeup :
2833250938 Ab489b2f15

Overview of whole driver ready for first light:
Case and varoius bits are from an old PABX from the tip

.
Driver is my own wierdo ,overcompilcated design, but hey it works great so far!
Primary feedback.
2832412317 12da8e86a5

25v first tentative test and it works first go, a rare pleasure (if you look close you will see the teeny 5cm streamers, ok for 25v I reckon):

Secondary with obligatory scale lighter:
2833252018 Db057aa941

Anyway , now I'm just waiting for sundown so I can ramp it up and see what happens !

Oh , almost forgot the other board type :
As you can see one pair of output devices mounts under the board, the whole lot fits onto one of the heatsinks shown in the other photos.
I figured these would be great for compact SSTC's, yet to build one up myself but rest assured I will!
2832036746 247f615030

Dr. SSTC

Sun Sept 07 2008, 12:57AM

Registered Member #1407 Joined: Fri Mar 21 2008, 07:09AM
Location:
Posts: 222

WoW great work dylan

i cant wait to see a full power test

anyways in that mean time you maywant to ask a mod to move this thread into the projects section

good luck

Dylan

Sun Sept 07 2008, 01:19AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Thanks Dr Arc

Don't know if I can wait for dark, its only 11Am here

, I might just ramp it up now and add a pic

.

Yeah , and moderators out there, please do move this, now that I've got my camera happening I'm going to cram this thread full of pics as things develop.
=== update :) ====

Couldn't wait, ready for full power test:
2835033508 20a54f574e

Lets try 80v :
2834197471 Df0bb49e2a

And slowly increasing burst width:
As I'm sure you all know the photos just dont do it justice

Then something let go in my feedback filter

, burst width became very unstable, mmm, I did forget suppression on the GDT, and was using only 100ma clamping diodes on the feedback, oh well, back to the bench

Mates

Sun Sept 07 2008, 07:30AM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

Hi, there is a serious flaw in your design - the filter cap should be connected with much stronger and shorter wires (ideally Cu-bars) because of inductance problems. Otherwise nice work man...

Dylan

Sun Sept 07 2008, 02:09PM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Mates wrote ...

Hi, there is a serious flaw in your design - the filter cap should be connected with much stronger and shorter wires (ideally Cu-bars) because of inductance problems. Otherwise nice work man...

Yeah, I need to cut and bend some new bus bars for this bridge,and rearrange the layout in the case a bit, I was just a bit impatient to fire it up!
I normally use aluminium bus bars,but was using the twisted pair for testing,I just couldn't resist turning it up. Turns out I blew one very underrated clamping diode in the feedback filter, and one of the gate driver chips.
Oh well, doesn't pay to cut corners with HV!

Tom540

Mon Sept 08 2008, 05:58PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

Thats not entirely true. If you put a film cap right across the bridge as close as you can then you can have your lytic farther away. I made two coils that had doublers that were about that same distance away from the bridge without problems.

Steve Conner

Tue Sept 09 2008, 10:00AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

That's not entirely true either. Film caps have lower ESR than electrolytics, so if placed at the end of long busbars, they can cause resonances that just make your life even worse.

The thickness of the bus wires probably doesn't really matter as much as the loop area enclosed by them. I've seen lots of hobbyist designs that used massive busbars and then shot themselves in the foot by leaving 2 inches of air between them. A pair of tightly twisted 12AWG wires would probably have worked better.

I'd still have stuck that capacitor right in between the heatsinks to get the wire length down.

PS, another solution is to never run your DC bus voltage above half the rating of your devices. Since the circuit strays are parallel resonant, they can't ring up to more than twice the DC bus voltage, so the result is that stray inductance just hurts your performance instead of blowing your devices to heck. Richie Burnett told me about this one.

MRacerxdl

Tue Sept 09 2008, 11:17PM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Film caps cause ressonance? I think that is because my DRSSTC wont work with some Poly Film Caps (Siemens 1uF 400V) in parallel of the primary bus. (It works but very poor)

Dylan

Fri Sept 12 2008, 02:54AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Ok,
If you look closely you will notice the two (black and red) Poly caps mounted directly on the bridge board, then the twisted pair (about 15cm of it) to the main bus cap. It should be fine as is I reckon, as I have used similar setups at much higher powers without any problems. This is however my test rig , and once I have things tuned and set up right I will be re-casing this coil and using short Ally busbars to the filter cap as well.

Anyway , I got the ebay ad up if anyone wants to grab a few of these boards:
Blatant ebay add, hope thats ok?

Steve Conner

Fri Sept 12 2008, 09:39AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

You'd probably have more luck advertising them in our Sale & Trade board if you haven't already.

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