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Wow, check this: 1200V, 33A, 100mOhm 90nC gate charge MOSFET !




 
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Author Topic: Wow, check this: 1200V, 33A, 100mOhm 90nC gate charge MOSFET !  (Read 14451 times)
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steve_qix
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« on: April 06, 2011, 07:32:38 AM »

The new CMF20120D silicon-carbide MOSFET looks like an amazing device.  1200V, 33A continuous, 90nC of gate charge.  It has 1/10th the R-DS on of the FQA11N90, will handle 3 times the current and will switch much faster.

These types of devices will definitely be in the future of class E and other solid state equipment.

Unfortunately, at about $94 EACH DEVICE (price from Digikey), the MOSFETs for a 24 device transmitter usually costing around $84 would cost $2256.

But, the device capabilities are certainly impressive.  I wonder when/if the price is going to drop to something reasonable (like under $10/device)?

Has anyone here worked with any of these or similar devices yet?
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« Reply #1 on: April 06, 2011, 10:15:45 AM »

Steve,
I've been watching them for a while now. Reminds me of my first class D with 4 IRF250 on 75M back in the early 80s. I think it took me 3 days to blow the finals. Back then the FETs ran about $80. I cobbled 4 from an old breadboard at work. I knew they would work at RF because I saw them oscillate at close to 100MHz with a poor layout. We've come a long way baby.
BTW, I'm still running the same TO3 Totem pole drivers from that first rig in the 160 meter rig as predrivers. They have been in service for 25 years.
Maybe I'll change over to IXDD414s someday but the square wave drive to the finals looks good.
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W2PFY
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« Reply #2 on: April 06, 2011, 10:32:16 AM »

Hi Steve, if each one of those devices can handle about 40KW, why would you need 24 pills? There must be an answer out there? I am not a transistor guy at this point Grin Grin I'm not against them, I just have not worked with them in over 20 years.
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« Reply #3 on: April 06, 2011, 11:32:12 AM »

Yes, The concrete floor at work is very uneven and I believe it was one of those I used under the desk leg to eliminate the wobble.
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k4kyv
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« Reply #4 on: April 06, 2011, 12:25:33 PM »

Hi Steve, if each one of those devices can handle about 40KW, why would you need 24 pills? There must be an answer out there? I am not a transistor guy at this point Grin Grin I'm not against them, I just have not worked with them in over 20 years.

I haven't used one of those devices, but I would say it's just like vacuum tube ratings, 1200V, 33A continuous means that each device could withstand a drain voltage of up to 1200 V and would handle 33A continuously, but not simultaneously.  You would never run a vacuum tube at maximum plate voltage and maximum continuous plate current at the same time. There is a limit to the amount of power that can safely be dissipated, depending on what heat sink and other cooling is used. In switching mode, dissipation would be relatively low, but still not zero. In class H service there would be substantially more heat generated.

Wonder if anyone has tried water cooling, with coolant flowing through the heat sink as in a water cooled automobile engine. That should be much easier to accomplish than cooling vacuum tubes with water, as they did years ago in 50 KW+ broadcast transmitters.

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« Reply #5 on: April 06, 2011, 12:27:10 PM »

Hi Steve, if each one of those devices can handle about 40KW, why would you need 24 pills? There must be an answer out there? I am not a transistor guy at this point Grin Grin I'm not against them, I just have not worked with them in over 20 years.

Well, that's not an unreasonable question.  If you take what we're actually using now - the FQA11N90 - that device is a 900 volt, 11 amp (DC continuous) device.  Ok, that's around 9900 watts, right?  Well, not exactly.

With practical design criteria, you want 100% headroom with respect to voltage and current.  If you do this, you will have a pretty much bullet proof transmitter.

Ok, so we cannot exceed 450 volts peak and cannot exceed about 5 or 6 amps.  Now, sort of "back in" to the operating values values.

A properly designed class E RF amplifier, correctly tuned up, will exhibit peaks of approximately 3.5 times the applied DC voltage.  So, take 450 (this is the max voltage that will be seen across the MOSFET, leaving a 100% safety factor with a 900 volt device) and divide by 3.5 (the class E peak to DC voltage ratio) and that gives 128.5 volts.  So the maximum DC (under modulation) voltage we're ever going to want to put into the amplifier is, say, 130VDC using round numbers.  That will be the DC power supply voltage when using a series modulator.  Divide this number by approximately 2.8-something (to leave enough headroom for almost 200% positive modulation), and that's where I came up with the 45 volt carrier DC voltage figure that we're pretty much using for most class E rigs that are using the FQA11N90.

Now on the current side - 11 amperes DC - leave 100% headroom, so that's  5.5 amperes DC - and I leave some more headroom because the device actually conducting for less than 1/2 of the cycle (but MOSFETs have a high peak current rating, so we don't have to derate completely by less than 1/2) - so that's about 3.5 amperes or thereabouts.  There are other reasons for this value as well, including the R D-S on, which is a bit less than 1 ohm.  Divide that by 2.8 (remember, our almost but not quite 200% positive peak headroom), which gives about 1.25 amperes.

Now we have our DC operating values - 45V @ 1.25 amperes per device - about 56 watts carrier input, and at 90% efficiency, about 50 watts output per device.  All of these numbers are based on about 200% positive modulation and 100% headroom for voltage and current.  I usually run about 1 amp per device.

Anyway, there you have it.  Yes, in absolute theory one could run a WHOLE lot more power per device, but what would be sacrificed is the reliability.  That's not a sacrifice that's worth making under any conditions, unless you are the manufacturer and want to sell a lot of devices - and I see app notes all the time with no headroom, and that show an unreasonable power output for the devices in question.

So, in theory, one of these new devices I talked about in the first post of this thread will run about 3 times the current as the FQA11N90, and at a little more voltage - so, maybe 55 volts at carrier at 3.75 amps - or about 200 watts input per device, probably 180 watts output per device.

Regards,

Steve

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« Reply #6 on: April 06, 2011, 12:42:19 PM »

I'm thinking full wave rectifier off the 240 volt line making about 170 VDC as the positive peak.
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« Reply #7 on: April 06, 2011, 12:56:34 PM »

So, maybe a pair would be an economical way to get a 350W (carrier) class E rig up on 20M-6M?  Or is that axing too much of them?

T
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« Reply #8 on: April 06, 2011, 02:30:37 PM »

Might be better off with an IXYS FET. Cost still an issue.
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« Reply #9 on: April 06, 2011, 03:36:55 PM »

So, maybe a pair would be an economical way to get a 350W (carrier) class E rig up on 20M-6M?  Or is that axing too much of them?

T

Hi Tom,

It is highly unlikely that device could be driven much above 20 meters - even then, it would be a stretch.  The package and gate capacitance will eventually self-resonate - I'm guessing at around 20mHz or thereabouts.

10 meters calls for a device with much lower gate capacitance for class E.  My initial design for a 10 meter RF amplifier used IXYS *metal* gate MOSFETs - small MOSFETs running at around 200 watts totally.  I forget how many devices I spec'ed out.  But, that design will be surfacing, as 10 meters is OPEN!!

Regards,

Steve
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« Reply #10 on: April 06, 2011, 05:04:43 PM »

I looked up the specs on the MRF150 and agree 20MHz would be a crap shoot.
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« Reply #11 on: April 06, 2011, 06:41:28 PM »

10 meters calls for a device with much lower gate capacitance for class E.  My initial design for a 10 meter RF amplifier used IXYS *metal* gate MOSFETs - small MOSFETs running at around 200 watts totally.  I forget how many devices I spec'ed out.  But, that design will be surfacing, as 10 meters is OPEN!!

Regards,

Steve


Only been wanting that design to be shared for 4 or 5 years   :-)

Be great to see it!

http://classe.monkeypuppet.com/viewtopic.php?f=1&t=619
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« Reply #12 on: April 06, 2011, 08:40:12 PM »

10 meters calls for a device with much lower gate capacitance for class E.  My initial design for a 10 meter RF amplifier used IXYS *metal* gate MOSFETs - small MOSFETs running at around 200 watts totally.  I forget how many devices I spec'ed out.  But, that design will be surfacing, as 10 meters is OPEN!!

Regards,

Steve


Only been wanting that design to be shared for 4 or 5 years   :-)

Be great to see it!

http://classe.monkeypuppet.com/viewtopic.php?f=1&t=619

Right - now that there's a reason  Grin  With the band being useful, and all that!!!!
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« Reply #13 on: April 06, 2011, 10:44:25 PM »

Instead of water for coolant, use liquid nitrogen(LN2) for cooling a bank of those pills.
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« Reply #14 on: April 07, 2011, 12:16:40 AM »



Steve, what's the power rating given by the factory? (watts)

I know there are Phillips devices that run many hundred watts that are used in FM broadcast transmitters... I seem to recall that they are Mosfets, but that is a weak recollection. They are pricey... but.

Seems like the SiC devices are a tough fab, slow, low yields etc... as far as I can tell. There are audio devices (like this one) that are very promising, but no one has really tried to bring out a commercial unit using them so far... also iirc some small signal devices.

(sorry I am too lazy to go through the digikey site and look for myself)

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« Reply #15 on: April 07, 2011, 12:55:43 AM »

Yes, The concrete floor at work is very uneven and I believe it was one of those I used under the desk leg to eliminate the wobble.

I pulled the die out of one of them and used it as a preionizer electrode in a laser but of course it wasn't good enough so I had it made into a dental filling.
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« Reply #16 on: April 07, 2011, 06:37:12 AM »

Instead of water for coolant, use liquid nitrogen(LN2) for cooling a bank of those pills.

Liquid cooling saves space, but doesn't really cool the devices any better.  The thermal resistance between the die and the package is the limiting factor, once you can actually remove the heat from the heat sink.

Bear, the devices are around 150 watt dissipation devices, as I recall (I don't have the ratings right in front of me!).
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« Reply #17 on: April 07, 2011, 09:56:27 AM »

Switching losses dominate performance then RDS on second. Dropping 2700pf of the 11N90 to 1700pf of the Cree will help. Then the RDS on of the Cree will really help at .08ohms compared to 1 ohm of the 11N90. P= C*V*V*F. 150 watts dissipation is lower than the 11N90 but I don't think this will be an issue since we are more concerned with voltage rating.  
When you look at the saturation voltage of the 11N90 at 1 amp that is about a volt. At 50 volts VCC that is 2% loss
Now if you are running a 12 volt pulse on the gates that comes out to about 1.5 watts at 4MHz. That is another 3% loss
So right out of the gate with the 11N90 you lose 5% at carrier level.
The cree part is 10 times better RDS on and about 60% gate switching losses.
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« Reply #18 on: April 07, 2011, 09:51:59 PM »



Cree, eh? Those American native aboriginals have really moved into the 21st century with these SiC devices!  Roll Eyes

I dunno, it just popped into my head.
Blame the radiation/fallout.

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« Reply #19 on: April 09, 2011, 04:45:06 PM »

Here are some newer FETs of the last 2 1/2 years that may be appealing also.  I try to keep an eye on these. 

They are normal price range and all three of these are 600 V N-channel power FETs, TO-247 style of package, and have “good drive efficiency”/low gate charge for their size:

ST STY60NM60 RDSon 0.065 Ohm,  Id 60 Amps, Qg = 178 nC.

Fairchild FCH35N60 RDSon 0.079 Ohm,  Id 35 Amps, Qg = 139 nC.

ST STW20NM60FD RDSon 0.26 Ohm,  Id 20 Amps, Qg = 37 nC.
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« Reply #20 on: April 10, 2011, 10:38:54 AM »


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« Reply #21 on: April 10, 2011, 03:04:35 PM »

In 1995 coworker and I built a water-cooled 2 kW amplifier at 805 MHz at work. It used a bunch (64 I think) of MRF899 bipolars, in class AB1. We bored water passages through the block, then cross drilled crossovers, and tapped and plugged them on the sides, so that there was serpentine water passage directly under each transistor on each side of the cooling pallet. It worked extremely well, those amplifiers are still in service. I think we ran each transistor backed off, they were 150 W PEP rated parts at the time.

Water-cooled transistor amplifiers are in television broadcasting these days, and are 'the cat's meow' in for some new particle accelerator RF systems. In Europe they are working up to 200-300 kW output, big things, not cheap.

I'm still favoring tubes for power in excess of 50 kW or so.
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« Reply #22 on: April 11, 2011, 08:16:39 AM »




The ARF1500 is only a 500 volt (Max D-S voltage).  These sort of devices are very good for linear amplifier service - not so good for class E, where a higher voltage is better.  In class E service, you could run about 20VDC at carrier at - maybe 5 amperes.  They also cost over $200 EACH!  Tongue

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« Reply #23 on: April 21, 2011, 05:49:45 PM »

I have updated a list of FETs I tested 4 years ago with the 3 newer ones I mentioned above.  The list ranked the power FETs according to ease-of-drive; the higher the Rule of Thumb number, the easier the FET is to drive.

Go to this AM Forum topic to see the updated list :

http://amfone.net/Amforum/index.php?topic=10754.msg209862;topicseen#msg209862

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« Reply #24 on: March 13, 2013, 08:09:49 PM »

Stardate March 2013, 2 years later : (These are SiC TO-247 FETs.)

The Cree CMF20120D is now down to $33 at Digikey and Mouser.

The CMF10120D (160 mOhm RDSon, 47 nC gate charge) is ~ $17 at Digikey and Mouser.  This is twice the RDSon of the 20120D and 24 A Ic versus 33A Ic for the 201220D.  
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