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Upgrade of my high power single switch SSTC

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LAN_403

Mates

Sun Jun 08 2008, 08:21AM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

I simplified the design (it is powered straight by non-rectified 220V AC mains) and increased the power of my single switchâ€¦

How it works:
It employs three BUP314

transistors in parallel switched by TL494 followed by UCC37322/1 gate drive and GDT. The resonant frequency of the coil is 380KHz. The coil works in Class E and to achieve Class E at 2.5KW which the coil sucks from the wall needs a special trick. The PW of the switch pulses is very short (only 1us) and the switching frequency is only half the resonant frequency (180KHz). Big advantage of this concept is that through the opened transistor the C1 is discharged into the primary and this discharge has a very short peak (most of the energy goes within first 300ns). Thus, the turn off time of the transistors is not longer an issue and relatively slow IGBT type of transistor can be easily used. Such ultra short pulses are relatively easy to place to the zero voltage transitions of the L1/C2 resonator by simple tuning of the coil (at low input voltage). The huge C3 capacitor works as a non-inductive current limiter with very low resistance. It basically determines the AMP peak of the C1 discharge. The C3 is made of many PP capacitors (used in asynchronous motors) and by connecting and disconnecting some of the caps the power of the coil can be regulated.

Here is the video of the coil in actionâ€¦

Comments welcomed

Red - secondary waves
Black - driving pulses

BTW: Would be great if somebody could help me to solve a feedback for this coil - I'm sure it would increase the spark lenght...

Steve Conner

Sun Jun 08 2008, 10:31AM

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

Looks like you reinvented the OLTC with an extra capacitor.

Mates

Sun Jun 08 2008, 12:21PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

Dr. Conner wrote ...

Looks like you reinvented the OLTC with an extra capacitor.

I donâ€™t understand where you see similarities with an OLTC concept. I checked all the OLTC schemes on the internet and the only similarity I see, is that they are also connected to the wall plug-in.
The OLTC concept as I understand it is a substitution of a spark gap a by a semiconductor. It means that the switch device is in parallel to the L/C. Next, the power source for a common OLTC is rectified mains with some kind of current limiter (a choke or transformer). The driving pulses for the OLTC transistor are completely unrelated to the resonant frequency of the coil, usually kept in low bps rate. None of these features are part of my coil â€“ so why is it OLTC for you?

My coil has a transistor in series with primary and is in parallel with the resonant cap (class E concept). As a power source I use non-rectified mains and the driving pulses are exactly 1/2 of the resonant frequency of the coil (In case Iâ€™m out of tune, no or very little sparks appear).

Arcstarter

Mon Jun 09 2008, 04:45AM

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

Wow, Great coil! I think i will buy some igbts and other junk and make this. Thanks!

GeordieBoy

Mon Jun 09 2008, 12:36PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Just to avoid confusion, this circuit is not operating like a Class-E RF amplifier. If anything it is operating closer to a Class-C frequency doubler.

Class-E operation is characterised by a damped sinusoidal voltage waveform, where the switch turns on at zero-voltage and with zero-current.

Some info including waveshapes here:

-Richie,

uzzors2k

Mon Jun 09 2008, 02:21PM

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

Looking good Mates, and interesting driving scheme.

Mates

Mon Jun 09 2008, 02:42PM

Registered Member #1025 Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566

GeordieBoy wrote ...

Just to avoid confusion, this circuit is not operating like a Class-E RF amplifier. If anything it is operating closer to a Class-C frequency doubler.

Class-E operation is characterised by a damped sinusoidal voltage waveform, where the switch turns on at zero-voltage and with zero-current.

Some info including waveshapes here:

-Richie,

Thanks for the link and the Class comment...
I do not understand the Class C - how it works, whether it has also a resonant cap or not. Still, I believe the signal is actually damped - you can even see it on the osciloscope picture. The only thing which is different from classical classE operation is that I switch every second wave. I also tried to switch every negative wave (this means the full resonant frequency of the coil). It worked very well, but only two seconds - than I destroyed one of the transistors so I went back to the safe waters of the resonant freq/2 (BTW: paralleling of the transistors have the big advantage that you destroy only one, in case you make some mistake. The bridge design is never so generous...).

Any idea about the feedback for this coil?

GeordieBoy

Mon Jun 09 2008, 04:34PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Feedback will be a challenge if you have to drive it at f/2 !

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