The hunt for 10 MHz / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

The hunt for 10 MHz

previous 1 2 3 4 next

Move Thread

LAN_403

Marko

Sat Mar 04 2006, 09:58PM

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

Mosfets with low gate capacitances and high speed usually have high ON resistance, like this one.
1,5ohm is too much for such current, transistent dissipation is now smaller but we have huge ohmic losses.

And IRFZ24 is actually close to this mosfet regarding speed:

STP5NK50Z

15 10 32 15

IRFZ24

4,9 34 19 27

Driving in class E minimizes switching losses but it cannot lower ON resistance.

And it has incredibly small ON resistance, its relatively cheap and acessable so I think its very best choice for such small coils, i had two and cooked them

hvguy

Mon Mar 06 2006, 10:52AM

Registered Member #289 Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154

How about the MRF series of power MOSFETS? Perhaps the MRF151G? I have used these in HF amps before with great results.

Steve Conner

Mon Mar 06 2006, 11:33AM

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

The MRF MOSFETs are great, they are proper metal-gate RF devices that work efficiently up to 100MHz, but they were very expensive (like $120/piece) last time I looked

Dr. Shark

Mon Mar 06 2006, 12:23PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

There is a wealth of information about Class-E amps right here:

For example

discusses how to get 200W at 10MHz from a single IRFP440, which was $1 or so last time I checked. The key really lies within clever circuit design, not buying expensive semis.

Dr. Shark

Fri Mar 10 2006, 01:01PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I am now starting to get some promising results with my tiny SSTC with about 350 turns on a Vitamin C former and an f_res of about 4MHz.
I cannot drive it at resonance because my CD4046 PLL driver wimps out at about 3MHz, but even this far off res I just get breakout and some really painful sparks to my fingers. I am driving it with a circuit that is "kind of Class-E", but not tuned at all, so judging by how hot the FET gets (it sits on a fan-cooled heatsink), I think I am burning at least 100W for a few W of output power.
I got a kit for an LC meter that will allow me to tune the inductors to get into the right ballpark for correct class E operation once I get it working. Then I will just need an oscillator that goes fast enough for my secondary, or I could use feedback.

Marko

Fri Mar 10 2006, 02:15PM

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

For only 4Mhz royer is I think best idea.
Only wondered if someone could push it to more power without overvolting gates.

For your PLL coil you could use 74HC4046, it works up to 20Mhz,
or use gate driver IC + antena or feedback winding..?

ragnar

Sat Mar 11 2006, 12:11AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

joe doh wrote ...

I just get breakout and some really painful sparks to my fingers.

I sincerely recommend you in future draw 'really painful sparks' to a screwdriver or something, mate... Ground it =)

Plasmaniac

Tue Mar 14 2006, 01:16PM

Registered Member #206 Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72

I've tested my 1,5MHz coil yesterday. At 24V, just some 100mA went trough the primary and I had 1cm discharges... until the voltage regulators died and blew the driving circruit apart. I have no drivers left and the 1MHz oszillator I used to protect the bridge is dead also, but I've ordered driver and PLLs. I hope they arrive tomorrow. The new version will be completely in SMD and with audiomodulation (2PLLs).

Marko

Tue Mar 14 2006, 01:50PM

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

Nice, it would be great if you have some photos

And what did you actually use to drive it, you are talking about PLL and sme 1mhz oscillator..

Plasmaniac

Tue Mar 14 2006, 02:33PM

Registered Member #206 Joined: Sat Feb 18 2006, 03:17PM
Location:
Posts: 72

This is my setup:

I ground the coil directly into the driver for my feedback (yes, I know this is stupid, but it worked

and it is the perfect way to get your feedback. Diodes protect the driver's input from overvoltage). The oszillator generates the input signal if no feedback is available (e.g. when the primary is connected incorrectly) so the MOSFETs are still "ballasted" by the primary's inductivity(if f=0 the coil wouldn't have enough resistance to protect the MOSFETs from too much current). I've made the first test with just 1 MOSFET instead of a half-bridge due to lack of inverting driver...

I'll use a normal PLL driver first, if it works, I'll add an other PLL's VCO and drive it from the voltage created by the first PLL + my mp3 players output, so I have a FM modulation, don't I?

previous 1 2 3 4 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob