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Do all 2 transistor / 24V SSTC's have to use flyback transformers?

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Steve Hobley

Thu Oct 21 2010, 02:40PM

Registered Member #1731 Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52

I've been reading up on simple 2 transistor Tesla coils - like the one here:

What is the reason for using a Flyback transformer for the primary/secondary? Is it not possible to push enough current through the transistors to run a more traditional air cored design (albeit very small).

Steve

Steve Conner

Thu Oct 21 2010, 02:58PM

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

Google the "Skori tesla coil", an air-cored design that runs entirely off 24V. Unfortunately the planz are all in Hungarian.

Planz

dingo27

Thu Oct 21 2010, 03:35PM

Registered Member #890 Joined: Tue Jul 10 2007, 10:06PM
Location: Slovakia
Posts: 180

I think that what you posted is not sstc schematic, but flyback driver.

Sam Barros on powerlabs.org has a useful circuit with just one 2n3055

Ken M.

Thu Oct 21 2010, 06:11PM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

It is a SSTC schematic I have made one and it worked until I realized I made some bad design choices especially the ground wire for the secondary being a jumper wire. Managed to get it to run for about 10mins then spark length decreased dramatically and something started to burn, noticed the ground wire s insulation was discolored and slightly bubbling, pulled off the insulation and ran the coil, about 30sec I saw the ground wire glow red hot.

Steve Hobley

Thu Oct 21 2010, 06:39PM

Registered Member #1731 Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52

I checked out the Skori design - a little more complex, but the parts look quite easy to get:

Does anyone know what the function of C4/L4 in version 3? They are missing from his assembly photo - it looks like a simple LC network 50mH + 3.3nF - but I'm unclear as to its function.

Thanks,
Steve

Arcstarter

Fri Oct 22 2010, 01:45AM

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

Steve Hobley wrote ...

I checked out the Skori design - a little more complex, but the parts look quite easy to get:

I don't understand that schematic :P. I mean, what is with all the series diodes? I guess it is to clamp the bridge rectifier to ground when the diodes are forward biased, using the forward voltage drop to allow bias? And the GDT goes to the gates then through a bridge rectifier O_O. I guess those two things have something to do with some very off interrupt scheme. And how about this transistor on the primary. What purpose does it serve? And apparently the L-C you are talking about has to resonate at the freq of the secondary... WHAT?!

BTW, this is the schematic i am going by:

From this page:

Update:

About the transistor on the primary: TranyÃ³t PNP used to protect the surge re-changed, so the collector to GND is therefore not be subject to isolation, the hÃ¼tÃ¶felÃ¼letet connect the grounding (of course you can combine with another is not already installed)

As for the L-C circuit: C4 L4 and only later to be incorporated in the previous versions have already put it as a way to more stable the frequency (the Tesla coil can have more resonance) and much less prone to sparking the primary to the secondary (ie, it may be closer - closer to the coupling ).

MOAR UPDATE: This is what he stated about the string of diodes.

The voltage capacitor C4 D8 ... D12 -3 ...- limit at around 4V (a 3.6 V zener is more powerful it would be nice here, but it seemed like a better solution)
D1, D2, D4, D5 diÃ³dÃ¡knak fontos szerepe van abban is, hogy a fetek megfelelÃ¶ munkapontban mÃ¼kÃ¶djenek. A fetek gate feszÃ¼ltsÃ©gÃ©t kb. D1, D2, D4, D5 diodes have an important role also in the corresponding point-fets work. Fets the gate voltage of approx. +15V Ã©s -4V Ã©rtÃ©kek kÃ¶zÃ¶tt tartjÃ¡k. R1 Ã©s R2 csak addig hatÃ¡rozza meg a munkapontot amÃg a (TR1-en) visszacsatolt feszÃ¼lsÃ©g alacsonyabb a diÃ³dÃ¡k nyitÃ¡sÃ¡hoz szÃ¼ksÃ©ges feszÃ¼ltsÃ©gnÃ©l. +15 V and-4V values are held. R1 and R2 only be determined by the set point until the (en-TR1) feszÃ¼lsÃ©g feedback diodes are required to open the lower voltage. Ezzel elÃ©rhetÃ¶ hogy a 2 fet lÃ©nyegÃ©ben felvÃ¡lva fog kinyitni, illetve lezÃ¡rni. This way that the 2 fet felvÃ¡lva will essentially open or closed

This is giving me a raging brainor.

Ken M.

Fri Oct 22 2010, 05:06AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Him using various parts which could be implemented with better parts is probably due to him being in Hungarian, and having a limited budget.

ManiaC

Fri Oct 22 2010, 05:57AM

Registered Member #2763 Joined: Sat Mar 27 2010, 11:48AM
Location:
Posts: 14

it is possible to do one transistor (NPN) Tesla coil
below the pictures of my Tesla

schematic & PCB

uzzors2k

Fri Oct 22 2010, 10:06AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Alas, had he only been in English so better parts were available.

Steve explains how the circuit functions further up in the thread Ken linked to.

Steve Hobley

Fri Oct 22 2010, 02:42PM

Registered Member #1731 Joined: Thu Oct 02 2008, 02:22PM
Location: Indiana
Posts: 52

Yeah it's confusing me too...

Regarding the SF18 diodes, the key attribute seems to be the 35ns switching time - I don't seem to be able to find much info in datasheetland regarding timing. Is 35ns something special, how fast does a "regular" diode switch?

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