[AMPS] Portable linear using a DAF?

[Tom Rauch]

> >You won't because a switched HV supply will cost more than the 
> >entire PA, and is more difficult to engineer.
> >
> 
>   The engineering is not that hard.  Two chips can take care of most of
> the work.  

The single most difficult aspect of the design is the transformer.
A close second is RFI suppression, and switching devices at the 
two or three kilowatt level.

>    At the 500 watt level you can use the old (i.e. inexpensive)
> International Rectifier, or Motorola (now ON Semiconductor) IRF450 FET
> family or equivalents.

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.

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. 
 
>    If you have some convenient chassis, to heat sink the FET's, then the
> whole rest of the supply will only weigh a couple pounds (1 Kg).

A few kilowatt few kilovolt supply that will handle a couple kilowatts 
or more output only a few pounds? I want one! 
 
>   Diodes are no problem, either.   1N6517 (5000V, 1A, 150nS, in a package
> the size of a 1N5408!)
>   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. 

 
73, Tom W8JI
w8ji@contesting.com

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