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Re: Linear power FETs
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What, the 350V one?

The 200V ones have been around a while; I guess they expect you to cascode  
for more.

You never did say what voltage you're targetting. Don't put your foot in too  
deep either :-)

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
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Re: Linear power FETs
snipped-for-privacy@yahoo.com wrote...
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 LMG3410R070, 600V 40A GaN, 100V/ns, integrated driver and protection.


--  
 Thanks,
    - Win

Re: Linear power FETs
On Friday, January 11, 2019 at 2:01:56 PM UTC-5, Winfield Hill wrote:
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That's very interesting for power conversion and solid-state drives.
Sweet.

I have to make accurate fast rectangular pulses with flat tops and
high edge timing accuracy, so for now I'm wary of having that much
complexity between my trigger and the output signal.

Thanks for the heads-up on a nice part.

(I posted the linear-mode FETs partly with you in mind--ISTR you
were interested Once Upon a Time.)

Cheers,
James Arthur

Re: Linear power FETs
snipped-for-privacy@yahoo.com wrote...
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 There's very little in the signal path.  And the 20ns delay to
 *the MOSFET output* is about as fast as you'll find.  My only
 complaint is that the FETs are too big, too much capacitance.
 When switching a 50-ohm cable-matching output resistor, a low
 70-milli-ohm Ron is serious overkill.


--  
 Thanks,
    - Win

Re: Linear power FETs
On Saturday, January 12, 2019 at 12:37:54 PM UTC-5, Winfield Hill wrote:
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When you take tpd as of the driver+FET, 20nS isn't bad. But I
need sub-nS edge-timing accuracy, so 20nS and a resistor-set
slew rate are rather scary to me at a time when I'm worried
about logic threshold drift affecting my timings.

I think I can manage about half that delay using hand-picked
parts, without getting too fancy, and then having the whole
signal path available and under my control.

Also, mine is a totem-pole driver. I'd have to float the high-side
LMG3410, pass its logic commands through an isolator that can handle
insane slew rates, and power it all with a floating supply.

With the signal isolator, my delay would be approaching 30nS. I'd
have to use a similar isolator on the low side to match the high-side
delays.

All of that is do-able, naturally.  But I'm trying to avoid it, here.

And I don't trust most of the digital isolators when it comes to
jitter--who knows how much those modulated transmission schemes
jitter? Excess jitter is something this application can't abide.

I do love the LMG3410 though--it is a very tempting concept, and a
tempting part.

Cheers,
James Arthur

Re: Linear power FETs
On Saturday, January 12, 2019 at 12:37:54 PM UTC-5, Winfield Hill wrote:
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Hey Win, here's a smaller-sized version of the same concept,
driver-plus-GaN on a chip:
  <https://media.digikey.com/pdf/Data%20Sheets/Navitas%20Semi%20PDFs/NV6113%20Datasheet%20(FINAL)%208-28-18.pdf>

600V and 300 milliohms instead of 70 milliohms.

Cheers,
James Arthur

Re: Linear power FETs
snipped-for-privacy@yahoo.com wrote...
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 Wow, Navitas NV6113, GaN, 200V/ns, only $3.38 at Digi-Key.  And
 Octopart doesn't even know about them yet!  It looks hard to get
 heat out of the package, they say limited to 2MHz switching rate.


--  
 Thanks,
    - Win

Re: Linear power FETs
Winfield Hill wrote...
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 Hah, you have to register, complete with password, just to see
 a product list.  Well, at least Digi-Key shows three single-FET
 switches available now.  But their two-FET half-bridge would be
 far more interesting to those of us who like to make HV pulsers.

 BTW, WRT their stated 2MHz operation spec, the Co(er) spec, which
 is 16pF at 400V, that's only P = C V^2 f = 5 watts at 2MHz.  But,
 oops, with Rth-ja = 50C/W on 1-in-sq copper, that's dT = 250C.


--  
 Thanks,
    - Win

Re: Linear power FETs
On Saturday, January 12, 2019 at 3:20:53 PM UTC-5, Winfield Hill wrote:
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I get 16pF x 1 MHz x 400V^2 = 2.56W

But, that's assuming the driver dissipates power in both directions,
which isn't true.  When the FET is off and something else is charging
Co, the driver dissipation is essentially zero.  So, the actual 2MHz /
400V dynamic dissipation, unloaded, should be about 1.3 watts, right?

Cheers,
James Arthur

Re: Linear power FETs
On 13/1/19 6:55 am, Winfield Hill wrote:
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50C/W - ugly. That would practically limit you to about 2 amps average,  
at 300mOhm. That's just not... special.

Re: Linear power FETs
On Sunday, January 13, 2019 at 6:13:19 PM UTC-5, Clifford Heath wrote:
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Au contraire! Two amps is way more than I need, and I much appreciate
the reduced capacitances.  (Not all of us are trying to drive big metal
all the time, or launch EMI out into space. :)

There are lots of big wide-gap devices for big-power stuff. But we
don't have many choices yet when it comes to making a dinky lil'
signal generator.


Cheers,
James Arthur

Re: Linear power FETs
On Mon, 14 Jan 2019 10:13:11 +1100, Clifford Heath

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It might make sense thermally to parallel a few smaller parts, EPC
GaNs or these things.



--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Linear power FETs
Am 11.01.19 um 02:58 schrieb snipped-for-privacy@yahoo.com:

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That's probably what has become of Directed Energy.
They bought die from APT IIRC and put them into their
freshly developed stripline case.

They were the bee's knees some 15 years ago in ham radio
amplifiers but seem to have faded away, or I did not follow it
since my interest shifted to VHF+.

cheers, Gerhard

Re: Linear power FETs
On Friday, January 11, 2019 at 2:23:15 PM UTC-5, Gerhard Hoffmann wrote:
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Cool.  An internet search for "vhf fet PA power amplifier"
brings up some interesting designs.

Here's one: n77%% @ 2 meters, 500W
  https://www.researchgate.net/publication/309046370_ACKA_500_watt_power_amplifier_for_a_144_MHZ_channel_based_on_a_VHF_push-pull_power_mos_transistor

As expected, RF guys just resonate out bond wire inductances, something
I can't do when making fast pulses.

Cheers,
James Arthur

Cheers,
James Arthur

Re: Linear power FETs
On Fri, 11 Jan 2019 13:40:22 -0800 (PST), snipped-for-privacy@yahoo.com
wrote:

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Right. That's why RF dmos fets aren't good for pulses. Some are
optimized for a specific RF band.

2 GHz is easy. DC to 2 GHz isn't as easy.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: Linear power FETs
On Friday, January 11, 2019 at 6:58:36 PM UTC-5, John Larkin wrote:
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But I called out one, above, that's spec'd to tr=3nS @ 400V.  That
looked promising.

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Cheers,
James

Re: Linear power FETs
On 12/1/19 8:40 am, snipped-for-privacy@yahoo.com wrote:
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That paper, while only 5 years old, is using an LDMOS FET that's more  
than 20 years old. The analog TV transmitters it was made for have been  
retired locally after decades of service. Just sayin', our Indonesian  
fraternity might not be up with the very latest... and they don't show  
their circuits either.

NXP publish a lot of good app notes and reference designs. Some of the  
RF power amps span well over a decade of bandwidth, limited mainly by  
the bandwidth of the baluns they use to transform between 50 ohms and 6  
ohms (input) and 2-3 ohms output impedances. That's not really  
consistent with your claim that the lead inductances are just resonated  
out. If you look closely at the geometry of these transistors and at the  
reference designs themselves, in many cases the inductance starts to  
dominate over the capacitance only at some hundreds of MHz. So I don't  
think your complaint about RF FETs is entirely fair.

Google for "site:nxp.com RF power" to get all the good info.

The parasitics of a package that can produce 1800W CW over 1.8-400MHz  
must surely be rather small?

<https://www.nxp.com/products/rf/rf-power/rf-ism-and-broadcast/1-600-mhz-broadcast-and-ism/1800-w-cw-over-1.8-400-mhz-65-v-wideband-rf-power-ldmos-transistor:MRFX1K80H

Clifford Heath.

Re: Linear power FETs
On Friday, January 11, 2019 at 11:55:01 PM UTC-5, Clifford Heath wrote:
  
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Excellent point. Yes, you'd think their parasitics would have to be
small. "Unmatched" seems a promising magic keyword for pulse applications.

I skimmed through the listings, but I didn't notice any that switch
hundreds of volts, not even the RF Cooking transistors. I need that,
at the moment.
(I've made some of my own R.F. 'cooking transistors,' including my first
and only +23dBm 920MHz p.a.)(Of which about 2e6 were ultimately produced.)

One of my problems, currently, is that most of the high-voltage fancy
FETs are monstrous compared to my needs, so even though their figures-
of-merit Ron vs. Qg are worlds better than the older tech stuff, the
fact that they're 20x over-sized for my application makes them slower
than an appropriately-sized MOSFET.

Even the most nimble GaN garbage truck FET still isn't as gamely as a
silicon itty bitty unicycle FET.

Cheers,
James Arthur

Re: Linear power FETs
Am 12.01.19 um 06:39 schrieb snipped-for-privacy@yahoo.com:

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A bit smaller than the other transistors that were mentioned,
but nevertheless DC to 6 GHz:

<   https://www.mouser.de/datasheet/2/90/ghv27030s-947886.pdf

A nice driver, at least   :-)

Cheers,
Gerhard

Re: Linear power FETs
On Thursday, January 17, 2019 at 4:52:13 PM UTC-5, Gerhard Hoffmann wrote:
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Wow, that's one beast of a driver ;-)

Cheers,
James Arthur

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