[AMPS] Portable linear using a DAF?

[Radio WC6W]

On Mon, 30 Oct 2000 13:44:18 -0500 "Tom Rauch" <w8ji@contesting.com>
writes:
>

Hi Tom,

>The single most difficult aspect of the design is the transformer.

   The transformers are not that hard, unless you are realllllllly trying
to optimize them.  

   A large cup core should be just fine for the 500W level switching at
around 100KHz.

   And of course, it helps to be familiar with a some of the advanced
design techniques, such as splitting the secondary into two sections
wound inside & outside the primary, to reduce stray coupling &
capacitance.

>A close second is RFI suppression, and switching devices at the 
>two or three kilowatt level.

  How'd we get from 500W to 3KW?

  If the transmitter cabinet is good enough to keep all the ham freqs in
check, then it should easily handle the radiated RFI from the switcher at
any power level.


>I don't think a 250 watt output PA using a few kilovolts with a 
>switching supply would be a good idea, but then people like the 
>DAF circuit and I think that is a bad idea also.

  That's a different subject.  

  A small switcher is not that out of the question, though the effort
involved is almost the same as building a large one.
  
  And it would be kind of ironic to power a questionable 40 year old
concept with a state of the art SPS.  Why does my spell checker
consistently try to replace DAF with DAFT??? :-)
 
>
>IMO, I'd just use a few FETS at the 250 watt level running off low 
>voltages and be done with it with less money, more reliability and 
>less weight. 

   I've looked at this problem at length and by the time you get through
adding all the requisite output filtering on a transistor amp, tubes look
damn good by comparison (parts count)!
 
>
>A few kilowatt few kilovolt supply that will handle a couple kilowatts 
>or more output only a few pounds? I want one! 

  Yep.  4 lbs. per KW is a reasonable factor.

  You'll need larger (circa 50A) FET's, either IXYS or APT are good
sources, and larger magnetics which will actually be easier to wind --
fewer turns, larger diameter!

  And a fan...  even though this supply is about 90% efficient that
leaves 300W worth of heat to remove.
 
>>   And if you keep the cross sections small (B*dL), RFI is not that
hard to
>> control.
>
>I don't think so. 
>
>The main problem is filtering the lines so the supply does not affect 
>the receiver. That's a real chore even with 200 watt 13.8v supplies, 
>let alone the supply described. 

   That's because they are trying to meet a consumer price point.

   There are some really great brick wall filters which can stop any
conducted RFI. 

    And the PFC input switchers are somewhat friendlier in this respect
having a rather large L in series with the input rather than just
switching straight off the rails.

73,
  Marv  WC6W









*


________________________________________________________________
YOU'RE PAYING TOO MUCH FOR THE INTERNET!
Juno now offers FREE Internet Access!
Try it today - there's no risk!  For your FREE software, visit:
http://dl.www.juno.com/get/tagj.

--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com