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New ISSTC with discrete GDT driver

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LAN_403

Reaching

Tue Dec 26 2006, 01:58PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

okay, a few days ago i started my newest project which will be a fun project to play around with. long ago i had the wish to build a sstc without using driver ics etc but with no luck. now i experimented a bit and came up with a nice discrete driver.

the driver for this 11x22cm secondary has several features such as a onboard interrupter and a very exact adjustable oscillator. cause i run the bridge with halfwave rectified mains i dont have the possibility of building a functional feedback without using an antenna or something. so i decided to use a normal adjustable oscillator.

it is adjustable from 230 to 500khz and is very sensitive. a trim pot for phase adjustment is also onboard to adjust a 50/50 duty cycle. the interupter enables the oscillator via pin 4 of the 555 timer ic which works really good. a jumper on the driver board can enable or disable the interrupter so you have a wide variety of possibilities. halfwave rectified mains on the bridge in combination with an interrupter causes in a funny variation of sparks and sounds.

the coil is just under development and i finished the driver and tested it with a bridge up to 130volts and everything seems to work very well. you get the right frequency within seconds and the fun can begin.

heres a pic of the finished driver board

the output stage is a simple push pull arrangment of a bd135/36 with a halfbridge of irf9530/irf530 in push pull configration. the output waveform without load is a nearly perfect squarewave. with gdt connected the whole circuit is drawing around 100 to 150mA. the driver mosfets are staying cool.

with 130volts input i get around 15cm streamers, but with mains voltage i hope to get around 30cm with the small coil. more to come soon

Update

The First test on mains was relatively succesful. i burnt up my test secondary, the bridge and the driver are fine. heres a video from the first real test on mains with fun factor

secondary and primary got shorted and tripped the ground safety breaker so the bridge and the other parts survived, only the primary and secondary are baked together

Tom540

Wed Dec 27 2006, 03:12AM

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

That's cool, I like the simplicity. Sometimes it's more fun to have to twiddle knobs n stuff then to have everything automatic. What FET's are you using in the bridge?

Steve Conner

Wed Dec 27 2006, 12:44PM

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

That looks great Reaching! If it can put out enough power to set fire to itself, it's obviously working well

Reaching

Wed Dec 27 2006, 02:38PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

i use normal irfp460s in the halfbridge, so nothing special here, .some zeners, some tvs and a small decoupling capacitor. for the bridge i had to use a 1:2 gdt with 10primary and 22 secondary windings. cause i power my driver with only 15 volts, the gdt primary only see +-7,5volts or so,and that is not enough to drive the bridge on mains voltage.
the circuit is much forgiving , you can adjust the frequency etc within the run and nothin bad happens, even when the oscillator is running 100khz above the secondary frequency, nothing happens, you can adjust the jumper for cw mode within the run and nothing happens, and you can threw all the knobs around and have fun without blowing something up,.
to complete this project, i ordered some parts such as a nice case to make it look professional.

the next thing i have to try out is to use the oscillator for frequenies above 1,5mhz and try to audiomodulate it (okay the 555 put out a crappy squarewave at 1,5mhz but the mosfet driver bridge should do its job, even with a sinusodial input, the bridge put out a relatively good squarewave)

Reaching

Tue Jan 02 2007, 11:42AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

okay, some new infos.

my parts arrived today and i already build a second driver solving some minor layout failures,. within the next few days i can build the electronics in the case etc to make it look like a finished project. cause i thought of selling some prototypes i made 2 longtime testruns with a lenght of 10 minutes and 30minutes, the driver and the bridge seemed to like it, no blown parts and no overheating or so (handwarm nothing more after a 30 minute run)

i tried measuring the current but i cant believe the results. i used a normal multimeter with ac current setting, but its halfwave rectified so i dont know if the readings are true. the coil draws 12A @230V when the positive halfwave is in relation to the on time periode. when the on time starts or stops before the top of the halfwave is reached the coil draws less current (around 4 to 8 A) so i calculated a approximate current draw of around 4,5A, seems very much for a small coil, and the bridge is fused with only 6,3A so im a bit in trouble,

but who cares, everything is woorking and no blown parts after a week of fiddling, playing around etc,

teravolt

Wed Jan 03 2007, 04:56AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I like your stuff, especially your SSTC 2,3. I am trying to figure out why they have the sward like sparks and your DRSSTC has branching sparks. does anybody have any idias.

...

Wed Jan 03 2007, 05:24AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Long live the ISSTC!

Good luck with the high(er) freuiency coil!

@teravolt:
The sstc streamers are sword like because they run off fullwave rectified AC, which is just like a vttc. Most all almost cw coils that have >3" sparks will exhibit this behavior. The DRSSTCs run are interrupted, like a SGTC, so you get the classic branched streamers. Or at least that is how I have thought it was...

Tom540

Wed Jan 03 2007, 08:19PM

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

I was thinkng it might have someting to do with frequency as well. At least on my coils. My higher freq lashup coil (700KHz) had sword streamers even though it was interupted but my lower 200KHz coil also interupted had the branchy type. All my coild run off full wave rectified DC or a full bridge doubler.

Reaching

Sat Jan 06 2007, 09:16PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

finished the whole project today and put it on my site.

okay, its in german but the pictures say everything. click on the pics to view them in full size

Marko

Sat Jan 06 2007, 10:54PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I can't see any pictures neither in IE or firefox

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