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# How do I determine the primary turns needed for this PLL solid state Tesla coil? Answered

I have nearly completed my SSTC but I am unsure how many primary turns are needed, is it just an educated guess, or is it calculated?
There are no specifics on this on the website http://uzzors2k.4hv.org/index.php?page=pllsstc1.

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## 32 Replies

This site gives turn info for primary = 20 and secondary = 1500...
And I fixed his pin 7 to pin 8 for you. . . . . . . . .  A

The primary turns seem to vary between different coils but I can't figure out exactly why.

iceng (author)2011-08-19

Steve C is a knock out designer always adjusting his Tesla.

May I suggest you wind the most primary turns you know of,
because it's a lot easier to unwind a few turns then to add Some !

A

What would happen if I cut the MOSFET drivers out of the circuit?

iceng (author)2011-08-24

The mosfets wouldn't turn on either circuit
The 1:1:1 are gate drive isolating pulse coils ( Xfmrs )

Would I be able to power the circuit off 5A?

(I blow up one of the MOSFET drivers due to a circuit error)

iceng (author)2011-08-25

Make sure you vid it for us.

A

One last thing could you drive the GDT with Darlington transistors? (a circuit of mine I'm thinking of building, different SSTC)

Thanks.

iceng (author)2011-08-26

Sorry you can not.
A darlington is a current driven base-emitter ( mili watt ) to turn on main current.
As opposed to a MOSFET which is a small voltage driven gate-source
( micro watt ) to turn on main current.
The pulse xfmr and circuit is sized for driving voltage gstes only.

A

Then would it be possible to make up a circuit that will discharge a capacitor into the GDT to drive it?

iceng (author)2011-08-27

The 470 nF capacitor in series with 5 ohm resistor in your example and
the o.33 cap in my example are both circuits that discharge a capacitor
into the GDT to drive it !

A

So would this circuit work?

The transistors are driven off a 250kHz alternating signal (I know I wrote 150kHz) while the capacitors are being charged by a 12V source.

Dual primary GDT 1:1:1:1.

iceng (author)2011-08-27

Some problems with both sides

I'm going to be at Burning Man all week, no web no phone :-D

Sorry for the silly mistakes.

iceng (author)2011-08-27

Why turn on mosfets in series first One Then the other. . . . . . A

That part of the circuit would be the same as the PLL SSTC circuit.

iceng (author)2011-08-28

OK the primary should work. The secondary outputs need that 15VZ
for limiting the V-gate and shunting as a diode to near zero volts
negative to gate While the other gate is turned on..
The common core actively fires one gate while reverse bias the other.
The diode gives -0.5 volt instead of -12 Volts.

A

So you're suggesting that I shouldn't have the reversed polarity on the MOSFET gate while the other MOSFET is turned on?

iceng (author)2011-08-28

Yes use the Zener as I show to protect the Gate from over voltage and under
voltage.. Negative drive guaranteed zero is enough and -o.5V is enough is fine..

A

I will be using IRFP460's they have a gate to source voltage of 20V max, will the zeners be necessary?

iceng (author)2011-08-26

The 1:1:1 gate drive transformer.

Grengate (author)2011-08-27

Those are available . 199 or 300 turns.

A

GDT's generally only have about 10-12 turns.

iceng (author)2011-08-27

Silly me, GDT <==> Gate Drive Transformer LoL.

Probably works ( 12T ) for MOSFET gates.
Long ago, in SCR and Triac applications we used more turns
because these devices fire on a current pulse with some duration
in case the pulse occurs at AC line zero crossing.

A

iceng (author)2011-08-27

100 or 200 turnss

GDT's generally only have about 10-12 turns.

I've built a coil with 26 turns I'll play with that and hope the MOSFET's don't blow.

Thanks!

steveastrouk (author)2011-08-17

It can be calculated, but its usually made then measured. Measuring in the position you have it is very difficult. You need to watch the coil current waveform.

Steve