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Small Class E PLL Coil

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uzzors2k

Mon Jan 28 2008, 07:43PM

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

When I started this project I was going to use a half-bridge, but I ruled it out in favour for class E, which I have never tried before. The relatively high frequency of the coil make class E a natural choice, since it will save otherwise huge switching losses and make gate drive easier since only one small gate has to be driven.

The secondary coil itself is 7 cm tall of 0.15mm? windings and 5 cm in diameter. This makes for a self-fres of ~1.35 MHz. For the PLL I used Steve's DWSSTC driver and for power amplification a single BD139/40 gate driver and single IRF630 mosfet was used. I tuned the coil for class E operation yesterday, and during the next few days I will implement audio modulation and an interrupter. Tuning for class E wasn't too difficult, the only problem was the compromise between coupling and proper class E operation. I had to use very low coupling (compared to offline half-bridge SSTCs) in-order not to overdamp the primary LC waveform. Some proof of class E switching is needed of course. Drain and gate voltage are scoped, ignore the ringing, I think my scope is picking up interference from the coil.

1201548870 95 FT0 Perfect Class E Switching

Class E really rocks, I can run the coil CW for long periods of time with just a small passive heatsink on the IRF630. Cooling will now be needed for the secondary instead. Some pics of the discharge with 50V supply voltage.

ShawnLG

Mon Jan 28 2008, 11:27PM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

I love it. Is your scope display showing two traces? Have you tried secondary current feedback instead of an antenna?

In my attempt to break the smallest SSTC record. I went with class E because of it's simplicity and its ability to work with high frequencies. Getting breakout with only a 2N7000 is difficult.

Spedy

Tue Jan 29 2008, 12:05AM

Registered Member #964 Joined: Wed Aug 22 2007, 12:39AM
Location: Stockton, CA
Posts: 134

Wow, that's really cool. Is class E really that easy for the power output? It looks fantastic. Good job.

flannelhead

Tue Jan 29 2008, 01:22PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

That's a real beauty!!
I'm also going to make something similar. It's gonna be powered from 12v lead acid battery. The secondary is wound on a film canister (3.1 cm diameter, winding length 4.5 cm) with 0.1mm wire. I'll be most likely using PLL. Let's see what can I get out of that!!

BTW, would a IRFP240 or IRF540 be fine with that kind of a circuit?

uzzors2k

Tue Jan 29 2008, 02:40PM

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

Thanks. The oscilliogram is dual trace, with both drain and gate voltage shown simultaneously. It was taken with 12V test voltage, but the waveforms don't differ much at 50V. I haven't tried base current feedback yet, but I plan to do so soon. Antenna are just trouble when boxing up SSTCs. I can't recall your class E coil, did you make a thread about it or is it "unofficial"?

Class E requires very few parts, and is quite elegant. Tuning for proper class E switching is the only critical portion, and even that is easy. (A scope is required though) With a film can secondary the fres will be pretty high, so mosfets with small delays and capacitances are needed. Those mosfets should be fast enough Spark, and their gate charge isn't very large either. Try them and see! If you need IRF630s I've found piles of them in monitors.

ragnar

Tue Jan 29 2008, 03:26PM

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

**shameless hijack, because my thread of the same topic was ignored months ago**

Tom540

Tue Jan 29 2008, 08:30PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
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Posts: 617

Matt Bingham wrote ...

**shameless hijack, because my thread of the same topic was ignored months ago**

thats because hijackers are ignored, lol.

flannelhead

Wed Jan 30 2008, 01:39PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

Uzzors wrote ...

Class E requires very few parts, and is quite elegant. Tuning for proper class E switching is the only critical portion, and even that is easy. (A scope is required though) With a film can secondary the fres will be pretty high, so mosfets with small delays and capacitances are needed. Those mosfets should be fast enough Spark, and their gate charge isn't very large either. Try them and see! If you need IRF630s I've found piles of them in monitors.

Yep, the frequency will be high (calculated with javatc ~2.5 MHz). And that's why I'm gonna use 74HC4046 instead of the normal CD4046. Its output current/pin is 25mA, so I'll need a 220 ohm resistor from the VCO out to the BD139/40 bases, right? (I'm going to drive the circuitry with 5V, except 12V to the BD139 collector). Or could the VCO output (pin 4) be connected straight to the bases?

EDIT: One more question, what is thet 10R resistor on top of the dwsstc II schematic for? I can't see any reason for that. I suppose it can be left out if I use 74HC4046?

uzzors2k

Thu Jan 31 2008, 05:58PM

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

You had your thread, Matt

, but if your self esteem needs a boost be my guest... Beautiful coil Matt!

I think the 10 ohm resistor might be there to improve voltage regulation for the 4046. Being a VCO the frequency will be sensitive to supply fluctuations. Other than that I'm not sure what it's for, and I don't use one myself. 25mA isn't enough to drive the BD's hard enough to drive the main mosfet with good rise/fall times. I would use a 4049 buffer chip to take the strain off the PLL and supply enough current to the BDs. At 2.5MHz I don't know how well the BDs will hold up, even with a minuscule capacitance like the IRF630 has. You might want to use a gate drive chip, a really small, fast mosfet, or some better gate drive transistors.

Steve Conner

Thu Jan 31 2008, 06:48PM

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

I put the 10 ohm resistor there, together with a capacitor to ground, to try and keep noise out of the 4046. I don't know whether it's needed or not. I read that the 4046 is sensitive to supply voltage variations, so I took that to mean dynamically as well as statically.

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