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Author Topic: New Power FET -- 1250 Watts at 65:1 VSWR  (Read 6084 times)
K6OK
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Posts: 62




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« on: June 13, 2011, 08:22:15 PM »

Was just poking around... noticed that amazing strides being made in the power FET industry.

Freescale Semiconductor: "The MRFE6VP61K25H/HS delivers 1250 W CW output power at 50V, after surviving a 65:1 VSWR, and is operable from 1.8 MHz up to 600 MHz."

Supply Voltage - Typ (V)   50
P1dB - Typ (W)   1250
Output Power - Typ (W) @ Intermodulation Level at Test Signal   1250 @ CW
Test Signal   1-Tone
Power Gain - Typ (dB) @ f(MHz) 22.9 @ 230
Efficiency - Typ (%)   74.6

With 22.9 dB gain, it only takes 1 watt to drive to almost 200 watts.  No tuner needed if it can take 65 to 1.  $270 ea. retail.  There's also a 600 watt model for $187.

Who's going to homebrew a linear with one of these?  Smiley
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KD8MJR
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« Reply #1 on: June 13, 2011, 10:04:30 PM »

Oh Crap is that Sweeet  Grin
The writing may be on the wall for tube Amps.
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G3RZP
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« Reply #2 on: June 13, 2011, 10:47:04 PM »

No mention of linearity. Providing the 1 ohm load impedance will be fun, too. Efficiency will be less in class AB, and how do you get the heat away?
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W9PMZ
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« Reply #3 on: June 14, 2011, 02:01:51 AM »

If these are the LDMOS transistors we use them for cellular amplifiers, only ones suitable the frequency of interest.

For heat...  The transistors are directly soldered to the heat sink during SMT.  Problems include voids in the solder area that is monitored by x-ray.  Need to keep voiding to less than 10%.

Generally when voids exceed 25% IMD issues start to appear due to excessive heating.

Regarding SWR, output circulators are used.

73,

Carl - W9PMZ
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TANAKASAN
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Posts: 933




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« Reply #4 on: June 14, 2011, 08:26:51 AM »

Some time ago QEX had an article from a group of Japanese radio amateurs who used a similar device for an HF linear. Does anyone remember it? The biggest problem here are the power supply and heatsink requirements, assuming 50% efficiency you will need 50v at 50A and you will be generating 1.25 Kw in heat. That's a single bar electric heater worth of heat to dissipate, no shack heater needed in Winter.

Tanakasan
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KF7CG
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« Reply #5 on: June 14, 2011, 09:30:01 AM »

The power supply and heat problems are similar to the power supply and heat problems for a tube amp. With filament heat included a 1.25 KW tube amp will have about 1 KW worth of heat to dissipate also. The tube supply will have about 3KV at approximate 1/2 amp to supply so it will have healthy insulation requirements. The 50V supply won't have near the insulation requirements, but IR drop and safety current limiting will be issues.

Either way the problems are there, which set do you want?

KF7CG
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K6OK
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« Reply #6 on: June 14, 2011, 11:56:35 AM »

I'm behind the times... someone has already homebrewed a linear for 2 meters:

http://www.qsl.net/f1jrd/MRFE6VP61K25H.html

This video is impressive ... watch the FET take really high SWR:

http://www.youtube.com/watch?v=02v58cnb41o

73 Jim K6VAR
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W8JI
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« Reply #7 on: June 14, 2011, 03:16:54 PM »

I'm behind the times... someone has already homebrewed a linear for 2 meters:

http://www.qsl.net/f1jrd/MRFE6VP61K25H.html

This video is impressive ... watch the FET take really high SWR:

http://www.youtube.com/watch?v=02v58cnb41o

73 Jim K6VAR

Don't get overly warm and fuzzy about things like SWR.

Because it something take really high SWR under some conditions does not mean it can work at high SWR, and it does not mean it won't pop out of the PC board with a whole lot less SWR.

One of the most worthless ratings on a power device is output SWR limit. It is almost laughable.

For example, if the drain to gate breakdown voltage is 150 volts and the device is rated at 65:1 SWR it can easily blow up with as little as 2:1 SWR. A 50 volt device in push-pull linear service will have a peak drain to gate voltage of about 100 volts or so when everything is running perfect. As little as 2:1 SWR with an angle that causes excessive voltage can pop the FET even though it is "rated" at 65:1 SWR.

If the device has an SWR rating of 65:1 and you run it in an amp where it is dissipating 80% of rated dissipation in normal operation, and if we change the SWR to 2:1 with the right phase angle range, you can blow the device right up. It will not exceed the SWR limit, it will exceed the thermal limit.

Devices fail from exceeding any parameter. SWR does not trump voltage breakdown limit, dissipation limit, peak current limit, or anything else.  It is the lowest parameter that is exceeded determines failure, not the highest one.

I ignore things like SWR and look at current, voltage, and heat. One of those three will always be much lower than SWR.
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M0HCN
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« Reply #8 on: June 14, 2011, 03:30:04 PM »

The usual limit on the current generation of power MOSFETs seems to be thermal when used in linear service.

Several of the manufacturers have the bad habit of quoting dissipation at 25 degrees case temp, and in some cases when you derate for something you might actually manage to maintain, 75% of the rating goes away!

I would note that the test in that video has a rather short length of line shorting, so it may have been placed at a 'favorable' phase angle, but for all that, more robust parts even if you have to take the robustness with a pinch of salt is something to be welcomed.

I wonder if that VHF device would turn out to be acceptably stable (and reasonably linear) in a broadband HF rig? I am thinking maybe 4-500W output from a 1100W theoretical device would be a more reasonable target from a thermal management perspective.

As to power supplies, EBay, HP server DC supplies, 48V 3000W, probably get one for $50 or so.

Regards, Dan.
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W6RMK
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« Reply #9 on: June 14, 2011, 09:14:06 PM »

The usual limit on the current generation of power MOSFETs seems to be thermal when used in linear service.

Several of the manufacturers have the bad habit of quoting dissipation at 25 degrees case temp, and in some cases when you derate for something you might actually manage to maintain, 75% of the rating goes away!

Oh yes.. we were working with some of those cool Ixys devices.. Given the Theta jc, you'd have to have the CASE at -30C to keep the junction temp reasonable at rated dissipation.  And then you have to get the heat away from the case. Liquid cooling ...

And, as W8JI pointed out, a moment's inattention, and you just blew up a device from overvoltage or over current.  The guys developing the early high power Solid State Tesla Coils (which are basically a several kilowatt RF PA) described it well.  You start with a big box of FETs or IGBTs, and after you've filled a bucket or two with blown up devices, you'll have a decent design.  Push pull/H bridge designs look attractive, but shoot through will kill it quick.

However, I'm sure the same sort of thing was the case 100 years ago with tubes... so we'll find solutions.
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N3OX
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« Reply #10 on: June 14, 2011, 09:46:59 PM »

Given the Theta jc, you'd have to have the CASE at -30C to keep the junction temp reasonable at rated dissipation.  And then you have to get the heat away from the case. Liquid [nitrogen] cooling ...

There, I fixed it for you.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K6OK
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Posts: 62




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« Reply #11 on: June 14, 2011, 10:48:08 PM »

Thanks W8JI, M6ATV, and W6RMK for the interesting and informative comments.  The stated frequency limits (1.8 MHz to 600 MHz). The 1.8 MHz obviously coincides with 160 meters. Is the 1.8 MHz number a marketing strategy aimed at the ham market or is it coincidental?
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KA1MDA
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Posts: 543




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« Reply #12 on: June 16, 2011, 05:57:03 AM »

This looks interesting...

http://www.youtube.com/watch?v=8ziYqjMQGEQ

Tom, KA1MDA
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W6RMK
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Posts: 651




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« Reply #13 on: June 16, 2011, 07:39:15 AM »

Given the Theta jc, you'd have to have the CASE at -30C to keep the junction temp reasonable at rated dissipation.  And then you have to get the heat away from the case. Liquid [nitrogen] cooling ...

There, I fixed it for you.

Glycol  (and a chiller) is your friend

(LN2 is a bit too cool.. CTE issues and materials getting brittle)
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KD8MJR
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Posts: 2362




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« Reply #14 on: June 19, 2011, 07:54:25 PM »

The video with the end cap put on, and the FET powering a dead short kind of indicates to me that some sort of internal protection circuit is built into the FET, I bet the FET shuts down on very low impedance's! If it had not, that end cap could not have been screwed off with bare hands, it would have been red hot!
In any case that makes the design even more appealing to me Smiley

Best part is that Amps using these FETS should be a lot cheaper, since the FET is cheap and the protection circuitry needed is a lot less.
« Last Edit: June 19, 2011, 07:59:33 PM by KD8MJR » Logged
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