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GaN FETS




 
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VE3ELQ
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« on: November 10, 2016, 08:56:50 AM »

Gallium Nitride FETs are a rapidly emerging technology which may soon replace Silicon Carbide.
Transphorm have recently introduced their TPH3212PS in a TO220 package with a common source (finally someone did this) eliminating the thermal pad requirement for better cooling and greatly reducing Drain capacitance. Note that I measured a TO247 FET common Drain to heat sink capacitance at 55PF with a standard thermal pad.
These look promising for lower voltage high power RF decks at about 50V.  Have not yet been able to find a supplier.
If anyone finds a source or tries these out please post your results.
Specs here:   http://www.transphormusa.com/wp-content/uploads/2016/02/TPH3212PS_v1b.pdf

73s  Nigel
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« Reply #1 on: November 18, 2016, 04:57:44 PM »

The SOA curve is pretty good - actually, quite good.  The input C is fairly significant - a little over 1000pF as I recall from the spec sheet.  The gate internal resistance is not specified.

It looks as if one could run 30VDC at carrier - 90VDC total power supply voltage for 200% positive capability and there would be sufficient headroom (I like to go for 100% headroom).

The R D-S on is good - 85 milliohms.  You could probably run about 4A per device at 30V at carrier, all assuming 200% positive peaks, which is not too shabby.

It'll be interesting to see what the cost is  Wink
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« Reply #2 on: November 18, 2016, 05:15:19 PM »

I found a British site that has these for around $10.00 each (US).
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VE3ELQ
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« Reply #3 on: November 19, 2016, 08:04:45 AM »

Looks like ON Semiconductor have teamed up with Transphorm for this FET, and other GaNs, as the NTP8G206N.
DK has them here:   http://www.digikey.com/product-search/en?keywords=NTP8G206N%20
They also have this one which looks interesting:  
http://www.transphormusa.com/wp-content/uploads/2016/02/TPH3207WS_v4.pdf
Very high Gate C, good luck driving that.

Considering the price and marginal specs think I will pass for now.
The Cree C3M0280090D FETs at $4.00 are working super well for me on 40M and below.

73s  Nigel

Edit:  On further searching DK now stocks a variety of Transphorm GaN FETs, some look pretty attractive.
http://www.digikey.com/products/en/discrete-semiconductor-products/transistors-fets-mosfets-single/278?k=fet&k=&pkeyword=fet&v=1707&FV=fff40015%2Cfff8007d&mnonly=0&newproducts=0&ColumnSort=0&page=1&quantity=0&ptm=0&fid=0&pageSize=25
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« Reply #4 on: November 21, 2016, 12:06:43 AM »

Yeah,  I did a search a week ago,  after your first post.  Octopart (search engine of part suppliers)  had nobody but DK come up.  One part, listed as in stock, AND as factory special order, but with no price...

Calling them, they were confused too,  eventually turned out they JUST had got the shipment, and pricing wasn't processed yet.  Was a busy week or two, and I hadn't checked back.

$10 is a bit pricey, but not terrible.  At
least it's not in the dedicated RF transistor price range...
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« Reply #5 on: November 21, 2016, 07:24:02 AM »

Looks like ON Semiconductor have teamed up with Transphorm for this FET, and other GaNs, as the NTP8G206N.

Earlier this year, On Semi acquired Fairchild Semi. A lot of consolidation in this industry making RF capable transistors. Also Freescale and NXP merged, each having an RF transistor line. I forget which, but one of them had to spin off their RF line. Now the combined company is being bought by Qualcom.

Jim
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« Reply #6 on: November 21, 2016, 10:50:08 PM »

4 of the 50A devices *should* be able to run a kW.  30V @ 8.5A each, configured in 4, single device modules.  90V total power supply volts.

My main concern is the speed.  The gate resistance is not published, and the construction is actually 2 devices (more or less) in one package.

It may be the big devices won't function at 4 mHz.
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VE3ELQ
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« Reply #7 on: November 22, 2016, 12:01:35 PM »

The Tr Tf specs look pretty good at 12 and 9 nsec, should do 4 mhz no sweat.  The high gate C is offset by the low turn on of 6V (fig 3) for full saturation so gate charge is not that bad.
You could just test just one in half phase into a load and see what it does, save some $ in case its a slug.

73s  Nigel
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« Reply #8 on: November 22, 2016, 04:55:44 PM »

Yes the rise and fall times do look good.  It's the turn off delay in particular that has me concerned.  We'll see !  My intent is to get some devices and play around.  I have a heat sink all ready to go, with drivers, bypass caps and RF output transformers.  I can swap in whatever FETs I want.
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« Reply #9 on: January 30, 2017, 01:24:39 PM »

I bought some to try in my single ended (74HC240 osc/drv) 40m Class E TX so see how much better they faired than the ubiquitous IRF510 and yep they good!

Improved efficiency and more power, 16 times the price however so I'm not surprised!

Just hoping the price will come down.....
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VE3ELQ
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« Reply #10 on: January 30, 2017, 03:01:55 PM »

Which one did you use??  Any pictures of your project?
I tested a pair of TPH3206PS GaNs with NCP81074 drivers at 8V in single ended push pull at 14.35 mhz and found them to be excellent performers with extremely high efficiency.  They should work really well at 7.4 mhz.
73s  Nigel
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« Reply #11 on: January 31, 2017, 02:04:08 AM »

Hi Nigel, I used the 3206's, driven with approx 7V from the 74HC240.

Yes, VERY pleased with the performance increase.

Thanks for the recommendation!

Must take some pics and make an 'instructional video' too!

PCB attached. source and drain need to be swapped if 3206 is used...........

I either use 'Conventional' modulation and a modulation transformer or a small PWM using the UCC series, still mean to try the LTC6992 to replace it!

I've only ever run this to around 10MHz but will try at 14MHz and above when time permits.

Makes for a very simple 1-20W carrier TX depending on Voltage.

EDIT>>>>>>>

OK had a play around last weekend and have a 40W carrier and approx. 150W peaks. I've had to put larger ferrites on the PCB as the T68-2's were beginning to darken! The T80-2's run somewhat cooler. The GaN device seems to handle this effortlessly. The whole PCB is about the same size as an adult thumb.

So for Freq's below 60m (or so) I usually use an IRF640 and that's fine but for 40m and up these look the business

Regards from th' UK!


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