Linear power FETs

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
I'm making another fast pulse generator, shopping FETs, and
noticed a few possibly interesting gizmos:

RF MOSFETs. They're built for linear operation. At a glance, they seem
to have fairly beefy SOA curves.  Up to 600V, too.

"N-channel enhancement mode linear RF power MOSFET
Ideal for class AB and C industrial, scientific, medical, and
commercial applications.  
VDSS = 500 V  ID25= 10 A"
  https://media.digikey.com/pdf/Data%20Sheets/IXYS%20PDFs/IXZH10N50L2(A,B).
pdf

More choices:
  https://www.digikey.com/products/en/discrete-semiconductor-products/trans
istors-fets-mosfets-rf/285?FV12%80016%2C1f140000%2Cmu250V%7C2079%2Cmu270V
%7C2079%2Cmu450V%7C2079%2Cmu500V%7C2079%2Cmu600V%7C2079%2Cmu700V%7C2079%2Cf
fe0011d&quantity=0&ColumnSort10%00011&page=1&pageSize25%

This little guy has Rth(jc) = .25K/W--pretty impressive.
  http://ixapps.ixys.com/DataSheet/de275_501n16a.pdf

This EPC GaN is the FET of my dreams, but it only exists in
everyone else's dreams, too. (Spec'd since <2016, they're still
unexistium.)

  http://epc-co.com/epc/Portals/0/epc/documents/datasheets/EPC2050_prelimin
ary.pdf

This 650V part puts an enhancement-mode GaN FET in cascode with a
depletion-mode GaN JFET. It's real, and it's kind of interesting too:
  https://www.transphormusa.com/en/document/650v-cascode-gan-fet-tph3206psb
/

Cheers,
James Arthur

Re: Linear power FETs
On 11/1/19 12:58 pm, snipped-for-privacy@yahoo.com wrote:
Quoted text here. Click to load it

Just 6dB gain at 40MHz - that's almost DC.

Clifford Heath.

Re: Linear power FETs
On Thursday, January 10, 2019 at 11:26:23 PM UTC-5, Clifford Heath wrote:
Quoted text here. Click to load it

I skipped over the s-parameters, I was more interested in the
switching behavior.

It's a 500V FET with tr=3nS and tf=5nS @ Vdss40%0V.  That
was the interesting part.  Plus a decent SOA curve.  

Cheers,
James Arthur

Re: Linear power FETs
On 1/10/19 11:46 PM, snipped-for-privacy@yahoo.com wrote:
Quoted text here. Click to load it

Welcome back!  You've been a bit scarce since last spring, iirc.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
We've slightly trimmed the long signature. Click to see the full one.
Re: Linear power FETs
On Friday, January 11, 2019 at 12:44:48 AM UTC-5, Phil Hobbs wrote:
Quoted text here. Click to load it

Hi Phil!

I've been doing some pretty fun things, but hobby-level
electronics, nothing I thought would be very interesting
for sed.  I do still peek in to see what's happening.

Cheers!
James

Re: Linear power FETs
On Friday, January 11, 2019 at 3:05:14 PM UTC-5, snipped-for-privacy@yahoo.com wrote:
Quoted text here. Click to load it
James!, As a tadpole here on SED I'd love to hear/see any  
of your hobby level 'fun' stuff.  
The fare has been a little thin here.  

I'm doing this high side switch driving a heater to ground.
Looking at the circuit I got to work, I've got low pass filters  
everywhere, with little understanding... which happens sometimes  
when you're just trying to get something working.  

I think my circuit was missing some resistance on the inverting input.
(I tried to do some asci art, but too much of a Friday night buzz. :^)

High side GS resistor (on pfet) that is turned off by  
level sift 'grounded' base npn, with emitter resistor  
driven by opamp.  A resistor divider senses drain/load
voltage-compares that to error (in opamp) which drives  
emitter R.  

George H.  


Quoted text here. Click to load it


Re: Linear power FETs
On Friday, January 11, 2019 at 8:53:41 PM UTC-5, George Herold wrote:
Quoted text here. Click to load it

Like this?

              Q1
 V+ >--+-----+-. .-------+--------.
       |     | ^ |       |        |
      .-.   .- - -       |        |
  Rgs | |   |           .-.       |
      '-'   |           | | Rload |
       |    |           '-'       |
       '----+            |        |
            |            |        |
          |/            ===       |
   +5v >--|   Q2                  |
          |>.                    .-.
            |                    | | R1
           .-.                   '-'
        Re | |       /|           |
           '-'      /+|-----------+
            |      /  |           |
            '-----<   |          .-.
                   \  |          | | R2
                    \-|-- Vref   '-'
                     \|           |
                                 ===

That looks like an oscillator.  :-)

Cheers,
James Arthur

Re: Linear power FETs
On Saturday, January 12, 2019 at 12:58:21 AM UTC-5, snipped-for-privacy@yahoo.com wrote:
Quoted text here. Click to load it

Prezactly!  I killed the oscillation with a nF across R2(10k) and  
100 nF! of feedback C.
Quoted text here. Click to load it

Is there some better way to compensate?  
It's a heater thing so slow is fine.  

Thanks for the nice pic, I certainly miss your presence.  

George H.  

Re: Linear power FETs
On Saturday, January 12, 2019 at 11:00:55 AM UTC-5, George Herold wrote:
Quoted text here. Click to load it

C2 across R2 is anti-helpful.  The problem, in lay terms,
is that your op-amp is reacting very quickly, but to old news.

That is, it's over-reacting to feedback that is delayed in
time.  So you're creating a situation where you are already
driving Q2 appropriately, but Q1's output hasn't moved yet,
and your op-amp then tries to drive Q2 even harder even though
its existing drive level was already perfect (if it had only
waited long enough to see). C2 makes that worse.

The easy solution is to eliminate C2 and add in Rcomp. Rcomp,
sufficiently large, slows the op-amp response until the
feedback delay is inconsequential in comparison to the op-amp's
now-gradual corrections.  In that way, the op-amp is reacting
to a realistic representation of the results of that op-amp's
last output, and can make appropriate new adjustments.

Another way is to accelerate the feedback to the op-amp
so that the op-amp's information isn't so stale, such
as with feed-forward compensation. Here, that would mean
putting C2 across R1.  But if you don't need the maximum
speed possible, just slow down the op-amp. It's less ticklish.

Slowed down, the op-amp will make corrections gradually, then
have plenty of time to see the effects of those corrections,
then make even more corrections. Tada! that's also known as
'closed-loop feedback'. :-)

Did that make sense?

Cheers,
James Arthur

Re: Linear power FETs
On Saturday, January 12, 2019 at 12:42:03 PM UTC-5, snipped-for-privacy@yahoo.com wrote:
Quoted text here. Click to load it
Yeah thanks James.  I thought I needed some inverting R.  
I need something for the feedback cap to 'work' against.

George H.  
Quoted text here. Click to load it


Re: Linear power FETs
On Fri, 11 Jan 2019 21:58:18 -0800 (PST), snipped-for-privacy@yahoo.com
wrote:

Quoted text here. Click to load it

Is that a linear voltage regulator? There was mention of a highside
switch.




--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Linear power FETs
On Saturday, January 12, 2019 at 11:57:16 AM UTC-5, John Larkin wrote:
Quoted text here. Click to load it

I took it as a linear system but you're right, George said "switch."

If he literally meant hard-switching Q1, that's a different kettle
of fish. A PWM scheme with a slow feedback loop might make more
sense for that.

Cheers,
James

Re: Linear power FETs
On Sat, 12 Jan 2019 10:17:47 -0800 (PST), snipped-for-privacy@yahoo.com
wrote:

Quoted text here. Click to load it

Driving heaters from linear amps is messy. There's the square-law
linearity issue, and general inefficiency.

PWM is better for heater control.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Linear power FETs
On Saturday, January 12, 2019 at 1:38:33 PM UTC-5, John Larkin wrote:
Quoted text here. Click to load it
Right, this is going to run at a constant temp  
against a mostly constant background... So only some limited power  
range.  (at least that's my hope. :^)

George H.  
Quoted text here. Click to load it


Re: Linear power FETs
snipped-for-privacy@yahoo.com wrote...
Quoted text here. Click to load it

 Nightmare, 2x2mm passivated die with solder bumps.


--  
 Thanks,
    - Win

Re: Linear power FETs
On 1/11/19 1:33 PM, Winfield Hill wrote:
Quoted text here. Click to load it

Sure works though.  Everybody uses them in incoherent lidars--iirc the  
Osram triple-stack laser datasheet shows them.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
We've slightly trimmed the long signature. Click to see the full one.
Re: Linear power FETs
On 11 Jan 2019 10:33:08 -0800, Winfield Hill

Quoted text here. Click to load it

We use them. They're really no worse than any other BGA chip. EPC
should offer little eval boards but for some reason don't. We made our
own.

Cooling can be a problem, getting heat out those tiny pads. Topside
cooling is a nuisance.  




--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

We've slightly trimmed the long signature. Click to see the full one.
Re: Linear power FETs
On Friday, January 11, 2019 at 1:33:33 PM UTC-5, Winfield Hill wrote:
Quoted text here. Click to load it

Since I'm wrestling wire-bond parasitics trying to get my
FETs /moving/, passivated die with solder bumps sounds fantastic.
I just wish they'd start delivering them!

Cheers,
James Arthur

Re: Linear power FETs
Quoted text here. Click to load it

??? EPC eGaN FETs have been around Digikey for half a decade IIRC!

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
We've slightly trimmed the long signature. Click to see the full one.
Re: Linear power FETs
On Friday, January 11, 2019 at 5:37:21 PM UTC-5, Tim Williams wrote:
Quoted text here. Click to load it

You didn't read the OP, did you?

That's okay, we all put our foot in it sometimes. :-)

Cheers,
James Arthur

Site Timeline