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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.



Best Answer 6 years ago

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.

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 !


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

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)

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


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.


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

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 !


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.

Circuit GDT.jpg

Some problems with both sides

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

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.

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.


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

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..


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

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.


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


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.


Will it still work if you don't do this and just have maximum amount of turns before over coupling?