Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
hen918, Mon Jul 13 2015, 05:14PM

You couldn't get us a circuit diagram could you? I'm struggling to see where everything goes. :)

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Tue Jul 14 2015, 05:44AM

Sorry! :( I forgot!

Here it is. The 100R and 2pF at the secondary side simulate the intrinsic resistance and parasitic capacitance of the secondary in the simulator (these values are guesswork, I don't know the parasitics of the real coil.)

Edit: Picture removed. Reason: First post now has all the circuits.

In place of IRFP460A and MUR160 I am using IRFP240 and UF3003.

cheers
shaan

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
hen918, Tue Jul 14 2015, 06:39PM

ahhh, so is the R1 side of the secondary the output end of the coil, with no top-load?

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Wed Jul 15 2015, 04:51AM

Yes.

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
jdub1581hv, Wed Jul 22 2015, 01:45AM

I tried to build this with 20v zener and an SD20n60 mfet.. I cant get it to oscillate though...

All items I'm using:
20v zener
FXMG16 ultrafast diode
SD20n60 MFET (20A, 600V)
d882 NPN transistor
5w 0.22ohm
3w 15k ohm

with interrupter to base... any suggestions?

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Fri Aug 14 2015, 03:13AM

hi jdub.

Try reversing the primary connection.
If that doesn't work then increase the 15K resistor to 100K.
Also try to use duty cycle of 10% or lower with interrupter. Lower D/C increases spark length and keeps MOSFET cool.
What is your power supply voltage and how many turns are the primary and the secondary have?

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Fri Aug 14 2015, 03:18AM

I have updated the setup. Spark length increased to 3" with 40VAC quadrupled to 160VDC supply. MOSFET is still cool but the sparks are now even hotter!

Check it out here-> Single MOSFET SSTC Update - Tripled Spark Length

Cheers!

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
jdub1581hv, Sat Aug 15 2015, 01:54AM



Turned out to be a bad diode.. I have it working now.. I blew a couple of the smaller gate transistors so upgraded to a TIP29, but overall it's working well.
On your interrupter, are you toggling the 90v via mosfet?
I haven't been able to get that part working, so I run continuous at the moment.

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
jdub1581hv, Sat Aug 15 2015, 02:09AM

As far as my coil, it is tiny, 1 1/2"dia, 680 turns, using a flat coaxial cable spiral primary 8 turns.
My supply is a 75va 22v xfmr from a tankless waterheater with a full wave quadrupler for 70vdc.

Though I'm tempted to hook up some rectified mains for 160vdc and see how it goes..
All my parts were free so no "loss" there really..

Just trying to get the circuitry down before I build a "real" coil.. I'm thinking 6" x 20" #28/30

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Sat Aug 15 2015, 08:13AM

Hi jdub. Good to hear that ^^

I am using separate 12v supply for the interrupter, the mosfet takes 160V. The interrupter circuit is below.

NE555+IRF540N Interrupter

shaan

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
jdub1581hv, Fri Aug 28 2015, 12:08AM

Alright.. I just got my MOT rewire done 56v ac out after bridge rect about 100v, and a new coil built ...
4"dia 1400 turns of #28..

Thanks for the interrupter schematic also, was different than mine.
I was trying to follow the wiring in your vids for the int.

Is it sinking the current from base or supplying it?

I think this is how you have it, is that correct? (see img)

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Fri Aug 28 2015, 06:00AM

Hi jdub.

Looks like you've done it right.

In on state the mosfet in the interrupter shorts the voltage at the switch mosfet's gate pin to ground resulting in no net current flow and in off state should let the gate turn on and the oscillation take place for very short periods of time. Even 5% off-time of the interrupter is more than enough for good break-up. Higher off-time (i.e. higher on-time for the switch mosfet) will do nothing more than overheat the switch mosfet.

Keep it going.
Awaiting your sparks. ^^
shaan

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Perezx, Sat Aug 29 2015, 05:18AM

What is the reason of using D1+Q3? You can use something like 1.5KE15 to protect FET's gate.
And I suggest adding a HF capacitor ro the source-drain of FET. Something lke 1-10nf, if you find right capacitance, you'll get close to E-class and bigger sparks.

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Sat Aug 29 2015, 08:41AM

I am no expert but I guess D1 clamps the gate-source voltage to its zener voltage and Q3 in off state simulates another fast diode besides MUR160 clamping the source-gate voltage to -0.7V, and in on state "tries" to limit mosfet drain current to (0.7 divided by the source resistance) amperes. So a 0.1R instead of a 1R is better if interrupter is actively limiting on time to less than 5% of total pulse length and we want long interrupted sparks.

Also, I have tried adding many different value capacitors between drain and source. Something strange happened (I don't know what exactly), and as a result about a dozen of the expensive HV mosfets are dead. Hence the D-S cap-omission. ^^

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
jdub1581hv, Sat Aug 29 2015, 05:26PM


I have also had issues trying to add a "tank" cap .. That's really the only thing I don't like about this circuit..
I've tried both serial and parallel with pulse rated caps and the circuit just fails to oscillate. Though perhaps adding another UF diode from source to drain might help?

Aside from that I got the interrupter going with results very similar to your 1st vid, about 1 1/2 inch streamers. I have do shorten all my leads and redesign my primary and topload.
I didn't get enough 1/4" copper tubing to make a primary for my big coil, was short by 5 turns or so :/..

I used some older parts I was willing to destroy:
IRF740 mfet
2sc3598 npn bjt
39k 3w resistor
5w 15v zener
0.22 2w resistor

Going to replace the IRF740 with a SD20n60 now that I have the rest working well. :)

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Sun Aug 30 2015, 08:18AM

Nice to hear that!

Show us some porn of your setup if possible. :)

Regarding the cap: I think the primary is resonating with the parasitic capacitor(s) inside the MOSFET, which is variable and nonlinear. But, when we run this circuit freely then the system automatically chooses its resonant frequency depending on the combination of the parasitic capacitance, the primary inductance and the secondary feedback.

Although in this mode the operation is far from optimum and probably much inefficient, it seems "guarranteed" to work to some extent with almost any configuration, with high initial pulses and then coming down to its normal and inefficient state, generating huge waste heat. Much like a typical "slayer exciter".

The addition of an interrupter will let the first few high-current pulses go through the system and then shut it down for some time for the PS cap to recharge. The average power drain and waste heat will be minuscule but apparently the spark length will be double or more than without and interrupter. In my case I got it tripled. ^^

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
jdub1581hv, Sun Aug 30 2015, 01:05PM

Well it's no Sasha Gray, but here's the setup with the SD20n60 ...

Diode is a FMLG13 (from Projection TV) Ultra fast 300v 5a.
Other diode(base 39K) is there for adding straight ac for 1/2 wave if I wanted to..
Been trying different caps, this setup seems to work best for me (so far)..
Coil is a fresh wound 700t * 3 1/2" with #28 and HDD platter for top load.
Primary is 12t 14awg speaker wire using only one strand.

Still need to get rid of my long leads, but it's working well.
I also went back to a standard 555 oscillator with duty adj (had a hard time with freq on the one you provided).

I'll try and make a vid once I get things cleaned up a bit.. Maybe a family photo as well (10+ coils now from 2" tall to 2' tall)...

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Mon Aug 31 2015, 06:12AM

Hey! that looks good!

please post the interrupter schematic you are going to use.

thanks.

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Perezx, Mon Aug 31 2015, 08:59AM


This is not the best way.

Working frequency depends on secondary (+ topload + ambience) frequency. Primary circuit has to follow in order to form a resonant overall circuit. The most efficient primary also has to switch on/off at Zero Voltage and Current (thus called ZVCS) and put maximum amount of energy during single pulse. This ideal circuit is said to be working in E-class.
You can read Stewe Ward's "Class E SSTC" article on this site: stevehv.4hv.org, he shows the way how to check your setup.
Of course, all research about DS capacitor should be done with a lower voltage. I use 24V DC, which is enough to get small streamer.

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
jdub1581hv, Mon Aug 31 2015, 02:57PM


This is what I am currently using for my interrupter.
The chip in the pic is a sm 556 dual timer. I was going to use the other side to feed audio and see how that goes.

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Mon Aug 31 2015, 05:05PM

Hi Perezx. You are right this is definitely not the best way. But hey, with just an interrupter and higher PS voltage this thing can produce streamers that are anything but small, and the MOSFET doesn't get hot even after a 1-hour long session!

I dropped the idea of using a D-S cap for the reason that it instantly and silently killed a dozen of my MOSFETs. Obviously there are some mistakes I made that I am unaware of, but I think I don't need to remember them anymore. ^^

Personally I just want to see how far we can go without driver chips and resonant capacitors.

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Mon Aug 31 2015, 05:06PM

Hi jdub.

Thanks for the schema.

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
jdub1581hv, Sat Sept 12 2015, 09:12PM

Soooo .... I just built my "large" coil primary and thought I'd share since I mentioned it coming up short before...

I'll put a vid together this eve once i get it tuned ;)

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Shaan, Sun Sept 13 2015, 06:45PM

zOMG what!?

thaz way too cool man!!!!

p.s. i hope the huge air-gap between the primary and secondary won't cause any problem. i have noticed this circuit having a fondness towards higher coupling co-eff.

Re: My One MOSFET Driverless Tesla Coil with 555 Interrupter
Patric, Sun Sept 20 2015, 04:42PM

Beautiful Tesla! I think I will make my first semiconductor Tesla thanks to you!