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Class E Circuit

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Dr. Shark

Sun Apr 09 2006, 12:42PM

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

Hehe, I am also kind of cheating on the PCB part, this is what I am using:

It does what it should, but it is getting really croweded since I am adding components all the time. Also the layout is done by hand, not ideal for opertation at 4MHz...

BTW, how do you mangage to keep your semiconductors cool at 12V in? I was able to get a fan cooled heatsink cooking in seconds at that voltage, before the zero switching started to work

ragnar

Tue Apr 11 2006, 06:05PM

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

It is done.

I regret I don't have any impedance matching between driver/primary. He runs very nicely with a 4.75nF shunt capacitor and some tweaking.

The turn-on/turn-off times for the MOSFET are unideal (IRFP460 has too large an input capacitance, I feel), and the UCCs are struggling, but thats OK for now - I have found some power supply MOSFETs to salvage for later

I'll now say I'm officially addicted to the class-E amplifier. =)
It's a nice feeling to know that I have to get it wrong four times to blow up a fullbridge' worth of MOSFETs... hehe

1144778723 63 FT6870 Classe8criticallydamped

Dr. Shark

Wed Apr 12 2006, 11:25AM

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

Nice! You won the contest, the price for the first working Class E TC on 4HV is yours! I am falling back more and more, I have massive trouble with my osscilator section, and it does not help that I need to get lots of work done before I ...[go off topic too much?]
Now, what I'd like to know is, are you sure you are in ZCS? It is not visible from the scope shots, in fact the ringing on the drain suggestst that you are not. What you want the drain to do is to return smoothly to zero, not shoot down abruptly.

ragnar

Wed Apr 12 2006, 11:34AM

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

lol, cheers... there was a contest?
Waverider won it first, and he actually knows what he's doing. I'm no RF engineer.

I'm probably not even ZVSing or ZCSing, I don't have the best selection of potential shunt capacitors to use, so I'm mixing and matching with old messes desoldered from the dead circuit boards under my bed.

I did just spot a 2SK539 from a dead power supply board, which I'm dying to try out... Unless I'm reading my scope wrong (likely), the spikes are 7 x Vin... so this will give me some headroom, and I'd better get my 10:1 probes working, hehehe

2SK539 is 900V, 3A, 1.4-1.9nF input capacitance. I'll keep you posted on the results.

Thanks for the feedback Joe, with the exception of you and the two doctors (Steve and Waverider), everyone seems to just lurk atm..

Steve Conner

Wed Apr 12 2006, 12:03PM

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

Hi Joe,

Yes, I think BP has gone off tune in the opposite direction to you, his circuit has too high a resonant frequency and not enough damping, so the voltage returns to zero too early and comes slamming down instead of landing gently. I would try cranking the power to get a bigger spark that loads the circuit more heavily. Or tightening the coupling and increasing the shunt cap somewhat.

It's still pretty good though as he is actually soft switching

Desmogod

Wed Apr 12 2006, 12:35PM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

When it is actually stable and running correctly, are you going to audio modulate it and tie it in with your previous experiments with plasma speakers?

ragnar

Wed Apr 12 2006, 04:01PM

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

No audio modulation with this baby until I can get the discharge totally silent to begin with. Nobody likes a speaker that hisses

And with class E... errr, I think frequency shifting is my only choice... even then it might be nasty. Linear- and pulse-width- modulation seem out of the question.. unless I can desolder and resolder my shunt capacitors as fast as the audio. :P

Desmogod

Thu Apr 13 2006, 09:20AM

Registered Member #139 Joined: Sat Feb 11 2006, 11:01AM
Location: Perth, Western Australia
Posts: 358

If you scope out richies site (Which I'm sure you have) He achieves it by modulating the voltage into the final stage of the amp. Apparently, it's a bit of an iffy proposition to actually modulate the frequency because class E is such a narrow band.
His words not mine :P
Just an idea though.

ragnar

Fri Apr 14 2006, 02:20AM

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

By pulse-width modulation, yes, he affects the RF output by giving the gatedrivers/mosfets shorter pulses for less output, however with class-E, the shunt capacitor is critical at a certain value, which is why if you increase the input power or affect the loading you need to retune.

I put it to the test at 60V, smoothed with 10,000uF... beautiful results! 3" brushy discharge... but it exploded sometime afterwards; I was too much of a wuss to put my scope across the D/S, but I calculate it would be ringing up to 400V. What was tuned nicely at 36V will be horribly tuned at 60V.

The great thing was the MOSFET just went "Pffft." - none of this spattering and carbon blasting whilst I struggle with foot-on-wall to remove the plug. So I can destroy four class-E output stages as compared with blasting four MOSFETs to hell in a fullbridge simultaneously.

I consider this a 75% saving in silicon. =)

I'm wary of increasing the coupling too much more; I need to lasercut that former to separate primary from secondary.

5.75MHz, here we come =)

Marko

Mon Jul 03 2006, 01:06AM

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

Something to revive an old thread (rather than opening new one) =)

I just recently played with a mini class E coil.
I used PLL (firstly it was direct feedback to UCC, but I didn't want to push the button. Instead of adding NE555 I just added an 4046 wich gives much more possibilities)

Circuit works either from an antenna or base current feedback.
At first it was nothing impressive, some 1cm streamer forom 16V input.
Frequency is 1,4Mhz,

When I added an resonant capacitor and better decoupling to the power supply, the coil went nuts.

Operating at 16V I could draw an 3,5cm long arc from the topload, even without best ZCS tune. I have only cheap digital meters and I couldn't measure current reliably. It looked like it was about 1A.

I can use VCO pot to finetune ZCS if necessary. I got it almost perfect but mosfet still heats up a small heatsink to 50-60 degrees (and stays about there) after about a minute :/ (but without good ZCS it would boil water at that point).

Mosfet is IRFP450, a 1337 one (been in many SSTC's already and never died).

One important thing with such designs is to put an additional big filter cap physically close to primary LC.

This eliminates power supply inductance (behaves as a voltage source) and only inductance of primary and it's leads 'matters'.
Adding this cap really pumped the output, especially since I was using aligator clips on power supply

Unfortunately my camera's battery charger died and I have o recent pics of sparks

But here is an old one, while coil was jet simple direct-feedback single mosfet SSTC.

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