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40 meter 200W SiC FET RF Deck




 
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Author Topic: 40 meter 200W SiC FET RF Deck  (Read 12980 times)
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VE3ELQ
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« on: April 28, 2015, 10:30:05 AM »

Based on earlier experiments with my 80 meter deck at 8 mhz a 4 FET deck for 40
meters was constructed, optimized and tested. It utilizes 2 C2M0280120D SiC FETs in
parallel with a single IXDD614CI driver per side in push pull. The heat sink measures
3 by 2 3/4 by 1 1/2 inch from a old computer CPU with the fan removed. The RF
transformer was constructed with 2 separate 5 turn primaries on opposite sides of a
single T200-2 core. The 5 turn secondaries are interwound with the primaries and
connected in series to provide the positive and negative waveforms. Many other
transformer configurations were tried, they all worked, some poorly, but this one was the best.
Two O/P filters were tested, a series tuned LC with no loading cap for Class E and a
5 pole low pass Butterworth for Class D. The load was a beat up Cantenna measured at
46 Ohms. The deck was powered from an Variac to an isolating transformer with a full bridge
and 5000 mfd filter. Drive was from my VFO using divide by 2 into a pulse shaper
to 45% duty cycle and buffered with 5V logic level OP.

Drive was applied at 7.35mhz, gate waveforms looked reasonable but with a noticeable
rise and fall to the edges, not as crisp as on 80 meters. The B+ was brought up to
provide 150V peak RF sign wave at the load with the OP tuned for Class E. This
calculates to 240W RF power.  Input was 68.1V at 3.7A for IP power of 252W giving an
efficiency of 95%. The deck runs a bit warm and after about 5 min stabilized at just
able to hold onto it, yea I know not a very scientific measurement. The driver
current was 400ma at 15V so 6W of the heat was from them.  The deck was then
modulated to 100% with a 60V carrier level giving 178W OP with mod peaks hitting 290V
RF.  The peaks were clean, no flat topping as I was a little concerned about possible
core saturation of the RF transformer but none was seen and the core runs dead cold.
To stay within the combined current SOA of 20A with some headroom I think this deck
should be run at about 200W carrier level which requires about 3.2A, so with 45% drive
duty factor about 7A peak at the FETs and when modulated about double that to 14A.
The drain pulses are under 400V at full mod so lots of headroom within the 1200V
rating and that's with no drain caps. The class D filter worked well also with
efficiency down a little to 92% and the deck too hot to hold but the little CPU fan
back on the heat sink would cure that easily.

There is more to say if anyone has questions or wants scope traces or a schematic.
These FETs are winners on 40M as is this little deck. 200W on 40 meters will do quite
well. Once again I thank Cree for an excellent product. Now working on the next one, an identical deck only
with four 19A FETs and a T200-1 core for 80M. I really love these FETs. Pic attached.
73s  Nigel


* 40meterRFDeck.jpg (656.77 KB, 2048x1536 - viewed 1016 times.)
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« Reply #1 on: April 28, 2015, 11:43:26 AM »

Looks good!

I'm glad to see the efficiency was still good on 40, as I am starting a replacement RF amplifier for my current 16 MOSFET deck (40 meters).

Will be building one for Rattlesnake Island as well - same power level.

I like it !!

May have some questions in the near future.  Maybe we can hook up on the air sometime during the evening or possibly over the weekend.

40 has been very good lately.

Regards,  Steve
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K4RT
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« Reply #2 on: April 28, 2015, 02:02:11 PM »

Nigel,

Thank you for posting the info & photo, and I hope you will keep us updated. I would like to see the schematic.

73,
Brad
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« Reply #3 on: April 28, 2015, 02:29:59 PM »

Nigel,

Schematics would be gladly appreciated.

Thanks,

Phil - AC0OB
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ka1tdq
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« Reply #4 on: April 28, 2015, 04:54:56 PM »

Steve

If/whenever you want to get rid of your 16 FET rig, let me know.

Jon
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« Reply #5 on: April 28, 2015, 09:43:44 PM »

Steve

If/whenever you want to get rid of your 16 FET rig, let me know.

Jon


Well I was kind of thinking of rebuilding the 40 meter RF deck into a digital drive amplifier and use SiC MOSFETs.  Because I am so bad at metalwork, I re-use chassis and front panels over and over again.  I bet there have been 10 RF amplifiers built using the foundation that now houses the 40 meter RF deck  Smiley  I've had the metal components for more than 40 years.  I guess that's pretty bad, isn't it.  Should probably try to get better at metal fabrication.
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« Reply #6 on: April 28, 2015, 10:32:48 PM »

Metal fabrication, either you have it or you don't.  If you haven't mastered it by this time you should quit while you can before you hurt yourself.  Steve you should stick with what you're best known for, being a clip lead wizard Grin
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« Reply #7 on: April 28, 2015, 10:40:18 PM »

Metal fabrication, either you have it or you don't.
K1KBW's metal fabrication is what first attracted me to Class-E back in 2007.   Steve's "clip leads"?   Roll Eyes
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« Reply #8 on: April 29, 2015, 08:49:19 AM »

40 years and 10 RF decks!  That's cool... frugal too!  Well, you won't know if you don't ask.

Jon
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VE3ELQ
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« Reply #9 on: April 29, 2015, 09:17:32 AM »

As requested a hand drawn schematic attached.  One day will get a CAD app, any suggestions???

This is a simple amp based on QIX Steves excellent work with my own spin on it.
Drain caps are not needed for 40M with this transformer design. Transorbs are optional but there is lots of voltage headroom so probably not needed, I don't plan to use any.

Forgot to add that for the CW guys without mod peaks to contend with this deck would run well at the 400 to 500 watt level and be well within the FET specs. You could key the Enable lines on the drivers. It is perfectly stable with full B+ applied with no drive.
73s  Nigel

* 40MRFdeck.pdf (230.76 KB - downloaded 439 times.)
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VE3ELQ
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« Reply #10 on: April 29, 2015, 09:25:36 AM »

Looks good!

I'm glad to see the efficiency was still good on 40, as I am starting a replacement RF amplifier for my current 16 MOSFET deck (40 meters).

Will be building one for Rattlesnake Island as well - same power level.

I like it !!

May have some questions in the near future.  Maybe we can hook up on the air sometime during the evening or possibly over the weekend.

40 has been very good lately.

Regards,  Steve


Steve looking FW to another "Clip Lead Special" in 40m caliber 1KW meter bending hifi.

Love to chat on 40 or 80 anytime.  Hear you on at 30 over on 3873 but it gets pretty crowded in there so dont often break in. Figured this WE you would be testing your ethanol tolerance at Deerfield :-)  Will drop and Email and we can set up a sched on 40 AM and talk techie stuff.
Best 73s Nigel

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« Reply #11 on: April 29, 2015, 12:53:43 PM »

As requested a hand drawn schematic attached.  One day will get a CAD app, any suggestions???


73s  Nigel

Thanks Nigel.

I use LTSpice. It is FREE, downloadable, easy to learn, and lots of options.

Phil - AC0OB
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VE3ELQ
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« Reply #12 on: April 29, 2015, 06:11:26 PM »


[/quote]

I use LTSpice. It is FREE, downloadable, easy to learn, and lots of options.

Phil - AC0OB
[/quote]

Thanks Phil.  Got it loaded and played with it a little.  Looks good. For my learning curve I will re-draw the amp schematic. Its hard to break away from the old pencil and paper and many erasers.
73s  Nigel
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« Reply #13 on: April 29, 2015, 07:27:14 PM »

LTSpice is not a CAD program but rather a simulation software.  It is a great product and you cannot beat the price!  For CAD operations it has limited functionality.  There are numerous CAD products available, some can import LTspice files.  I have used Eagle with some success.  But I also use Autocad especially if I want to design the cabinet/chassis too.

Congrats on the 40 meter design.  I like these newish fets.  I think they will change how we look at class D/E. 

Question on your design:  did you omit drain shunt caps in your schematic for a reason?  Not needed on 40?

TNX

Peter
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« Reply #14 on: April 29, 2015, 08:48:50 PM »

He said earlier the drain shunt caps weren't needed for 40m Pete.


I use Eagle for schematic and board layout.
It exports board info in a format that most PCB manufacturers can use directly


http://www.cadsoftusa.com/download-eagle/
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VE3ELQ
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« Reply #15 on: April 29, 2015, 10:59:49 PM »



Question on your design:  did you omit drain shunt caps in your schematic for a reason?  Not needed on 40?

TNX

Peter

Peter this all started as a proof of concept design just to see how these SiC FETS would work on 40m, but turned out to be a nice little amp. I experimented a lot with the transformer and noticed the drain pulses changed with primary inductance.  Too little L they get very peaky high voltage, too much and they get fat low voltage and start to overlap between the opposite phase.  .3 uhy was just right providing a near 1/2 sign wave drain pulse and when combined with the opposite phase at the secondary the output is nearly a sign wave with a tad of cross over distortion.  Also the drain tabs on the back of the FETs are only .006 inch from the heat sink with a dielectric pad which forms a pretty good capacitor.  And thats all they need on 40m.
73s Nigel
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« Reply #16 on: May 03, 2015, 01:39:33 PM »

Nice work Nigel.  After talking with Steve at NEARfest this weekend, I'm going to experiment with a 4-FET deck using the $16 C2M0080120D FETs fed with two IXDD-614's.  We figure it should do 400 to 450W.  I'm going to start with 80M and then build a 40M deck.
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« Reply #17 on: May 03, 2015, 04:14:33 PM »

Nice work Nigel.  After talking with Steve at NEARfest this weekend, I'm going to experiment with a 4-FET deck using the $16 C2M0080120D FETs fed with two IXDD-614's.  We figure it should do 400 to 450W.  I'm going to start with 80M and then build a 40M deck.


Good stuff John.  I think 2 of those 37A FETs would do 450W so it should be bullet proof.  Was thinking of you guys at Nearfest, would love to have been there but its 12hrs in a car from here.  Glad you met Steve, he da man.  Please post a report when your project is up and running.
73s  Nigel
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« Reply #18 on: November 10, 2015, 05:43:33 AM »

Topic maybe a tad old but still looks like the best design for simplicity and efficiency to date.

Cree have further improved their range with a 3rd Gen device C3M0065090D, 900V, 36A, 65mR.

I'm hoping to try these in various configurations but as VE3ELQ seems to have a decent implementation already will start with that.

I'm only looking for 100W carrier so am sure 2 devices will be more than enough!

Regards to ALL from the U.K.

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VE3ELQ
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« Reply #19 on: November 10, 2015, 09:43:56 AM »

Topic maybe a tad old but still looks like the best design for simplicity and efficiency to date.

Cree have further improved their range with a 3rd Gen device C3M0065090D, 900V, 36A, 65mR.

I'm hoping to try these in various configurations but as VE3ELQ seems to have a decent implementation already will start with that.

I'm only looking for 100W carrier so am sure 2 devices will be more than enough!

Regards to ALL from the U.K.



John sounds like a great project. 
I have some reservations however about those 36a FETs for 40m.  Though I've never tried them other builders report they take a lot of gate drive V to fully saturate and are too slow for 40m.  The 10A  C2M0280120D FETs are very fast and drive easily at 7.4 mhz, they are much cheaper and have a 1200V rating providing plenty of headroom for higher voltage operation up to 70 or even 80V carrier level. This opens the door for direct rectification of 120V line power into the modulator to eliminate that big expensive power transformer.  Two of them in PP would easily give you 100W (400 PEP).  You will have to adjust (reduce) the secondary turns to give 100V peak RF for 100W into 50 ohms.  A toroid OP xformer allows for any ratio even partial turns and they run cold. If you want more power add some FEts in parallel and change the transformer secondary ratio.

I would also recommend a 3 pole low pass filter of two series inductors with a shunt cap between them in the OP for class D. This will give very low 3rd harmonics yet provide full band coverage with no tuning and a considerable reduction in size and cost over a tuneable class E configuration with only a small drop in efficiency because the 10A FETs switch so fast. The OP waveform at the transformer is nearly a perfect sign wave so requires only modest filtering. I found class E really messes up the waveform and I could not achieve a low enough 3rd harmonic to meet regulations but I probably didn't do it correctly.
Good luck with it and please report on your results.
73s  Nigel
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« Reply #20 on: November 11, 2015, 09:45:12 AM »

OK, just want to make sure we're talking about the same FETs here, these are 3rd Gen and the Gate C is 660pF, rise / fall times are fast @ 25/36nS compared to 11N90's they look somewhat leagues ahead and they've been proved to work well on 40m.

Could you please confirm that these FETs are unsuitable (on 40m) before a make a sizeable investment (Mistake!)

I'll put together a platform on a milled single sided PCB so I can test pairs of FETs but was really thinking the 3rd Gen ones were the best available.

Regards

JohnB
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« Reply #21 on: November 11, 2015, 10:34:34 AM »

OK, just want to make sure we're talking about the same FETs here, these are 3rd Gen and the Gate C is 660pF, rise / fall times are fast @ 25/36nS compared to 11N90's they look somewhat leagues ahead and they've been proved to work well on 40m.

Could you please confirm that these FETs are unsuitable (on 40m) before a make a sizeable investment (Mistake!)


The C3M0065090D FETs have been available for a while now.  When I checked the specs I remember that I had bought two back in June to experiment with.  Checked my design notes and yes I had tried them on 80 and 160m.  They performed OK on 160 but poorly on 80 getting very hot but I was driving the gates with 15V, never tried higher so they probably we not achieving full saturation.  Never even considered them for 40M. They got relegated to my parts bin where they still reside. I believe other builders have them working OK on high power 80M amps using a much higher gate drive voltage.  If you already have some by all means give them a try, drive them hard and see what you get.  Be very interested in your data.  Good luck,  Nigel
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« Reply #22 on: November 11, 2015, 11:48:58 PM »

I have used those FETs on 40 meters.  I have an experimental 800 watt (carrier power input) transmitter running on 40 using 8 of the 900V devices.  I run 15V of drive from IXDD414s - one per device.  15V is Cree's recommendation for driving voltage for these devices.

I have found with all of the SiC MOSFETs that the peak current rating may not be all that the spec sheet says it is, at least at RF frequencies. 

One of the problems is the duty cycle, and related to this, the period of time when current is actually flowing through the device.  With SiC devices, you need to run the duty cycle as close to 50% as you can get before there is overlap.  Even with a 50% voltage waveform, the current does not flow for the entire period (at least with class E).  The current flow is more like 30%.

This means that for a given power (current), the peak current flowing through the devices is somewhere around 3x the DC.

For reliable operation, I have been operating STRICTLY within the "DC Current Rating at 100 degrees C" of the device and NEVER in the peak region.

Anyway, some suggestions.  If you only want 100 watts, and you use two devices, you'll probably be just fine if you run enough voltage (I run 45VDC at carrier).

Regards,  Steve


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