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DRSSTCã€€waveform. GDT,feedback,and more

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naok

Wed May 11 2011, 01:31PM

Registered Member #3128 Joined: Thu Aug 19 2010, 12:23PM
Location: Tokyo,Japan
Posts: 17

Hey all,it's been a long time.I'm fine with radioactivity,haha.
Thanks to your help, I could have 37inch long spark when it input 90VAC(voltage doubler).
But,my IGBT is very easily broken.and I want to have 40inch spark.

Today,I want you to see some picture about waveform.
If it's too bad waveform,Teach me how to change for the better.

I think it's bad waveform about "Q1-C","Q2-C","feedback-D",and "befor MMC-after Primary coil-B".
But I Can't judge it "no better waveform" or "too bad waveform".

Richie Burnett's web site was a good guide about GDT waveform.

Electronics H-bridge of 40N60 mini-brick IGBTs.
Tank Cap 7 parallel strings of 2 series .15uF 2kV caps (942C series by CDE).
Primary 7.5 turns of .25" cu tube. 11" diameter form, .2" spacing between turns, tapped at 4 turns.
Secondary 6.5"x23" winding of 30awg magnet wire. Single coat of epoxy for protection.
Toroids 24"x6".
Filter capacitance 2 series 10,000uF 250VDC electrolytics for 5,000uF at 500VDC.
Best Spark 37" point to point. input 90VAC.
110bps
ontime : 135us
variac : max130VAC 10A

driver and bridge

waveform

naok

Fri May 20 2011, 03:19AM

Registered Member #3128 Joined: Thu Aug 19 2010, 12:23PM
Location: Tokyo,Japan
Posts: 17

Oh? I haven't received any responses yet.
Does that mean there's nothing wrong with the waveforms in the photo?

MRacerxdl

Sun May 22 2011, 01:03AM

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

I think the waveforms are OK, The only strange thing is that waveform that you writed "Too long delay".

I got even worsed waveforms at primary, but my coil was working perfect with 1m sparks, see at this post:

naok

Sun May 22 2011, 05:46PM

Registered Member #3128 Joined: Thu Aug 19 2010, 12:23PM
Location: Tokyo,Japan
Posts: 17

Uh,I see.

I suppose,"Too long delay" waveform may be caused by too raise up secoundary.
but,if lower secoundary,I see frequency splitting.

I know,if DRSSTC size is large,frequency splitting is bad waveform.

mmh...It's difficult problem.

sorry,my very broken English.
I pray to solve your problem, too.

thanks!

MRacerxdl

Sun May 22 2011, 09:21PM

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

The frequency splitting is normal, you need to detune the primary circuit until the second frequency gets off.

My Coil runs with the secondary at 110kHz, but the primary is only at 100khz. That gaves me about no upper pole frequency, and all circuit runs about 100khz.

Goodchild

Mon May 23 2011, 07:00AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Just out of curiosity why did you add the 2.2 ohm resistors in series with the GDT primarys?

Also you are going to want to put your driver onto a perf board or PCB and also into a metal case before running any kinda output. If you don't it will interferer with your driver sometimes creating a nasty positive feedback loop pushing your DR into CW. I have bad this happen before with this driver when not put into a grounded case. Think of a SSTC and how it get it's feedback (antenna), your bread board is basically a bunch of antennas

MRacerxdl

Mon May 23 2011, 03:58PM

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

LOL, I didnt see the breadboard below.

Goodchild is right, you can test it with breadboard, but it wont work at higher powers, and even at lower you will get much loise.

You need to mount it at a PCB, you can make at a universal board, but make a shield to prevent more noises.

naok

Mon May 23 2011, 06:38PM

Registered Member #3128 Joined: Thu Aug 19 2010, 12:23PM
Location: Tokyo,Japan
Posts: 17

Hi, MRacerxdl and Goodchild.
>>why did you add the 2.2 ohm resistors in series with the GDT primarys?

because it's simple reason that is very easy methd to stop overshoots with the GDT secoundary.
It's no soldering,and easy repair.
At first,I changed resistors value with the GDT secoundary.
but,I couldn't stop overshoot even if I changed value over 25 ohm.
And gate couldn't open.
because I add the 2.2 ohm resistors in series with the GDT primary.

I understand my bread board is basically a bunch of antennas.
because,my aluminium case guard my driver board against EMC ï¼š-ï¼‰
(The case cover is removed temporary in my up-loaded pic. ).
but,Goodchild and MRacerxdl said about same problem.
OK! I understand, I need to mount it at a PCB board and I will make a shield with aluminium case.

Thanks a lot for your advise!

MRacerxdl

Mon May 23 2011, 07:48PM

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

It wont stop the overshot, only reduce them. And putting it at the GDT primary wont change it (I think). Also, all current is gonna flow with these resistors and the charge can be unbalanced with all igbt's (and one can switch before another).
So the best is to have one resistor per IGBT gate. And also zeners the zeners to clamp it. I think 5 or 10R per gate is good (that is what I use)...

Arcstarter

Tue May 24 2011, 03:44AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

It would be a good idea to reduce the length of the wire connecting the buss capacitor. Your long wires will introduce a lot of inductance too.

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