Class E ( and I think also probably Class D but I am not sure about that
one) will only give maximum efficiency at the design power loading. You
cannot tune for max smoke (well you can if you have dissipation capability
in hand but you will not get the 90% levels) My test 150watt 137kHz PA
achieved 93% on the bench, but it has to be tuned with a scope for the
correct drain waveforms. ( the stage is perversely tuned about 10% below the
operating frequency) This is best described in Prof. Nathan Sokal's article
in QST (or was it QEX).....Nat invented the mode in the 1970s. The lost
efficiency is due to switching the FET on and off at slightly the wrong
times. Best efficiency is also at the higher voltages. At 12 V the Ron*Idss
product is a substantial portion of the 12 volts available. A higher voltage
also increases the output impedance and leads to lower peak currents and
less loss in the caps and inductor and the leads. It is a fiddly narrow band
PA.
Cheers de Alan G3NYK
----- Original Message -----
From: "John Pumford-Green GM4SLV" <[email protected]>
To: <[email protected]>
Sent: Sunday, November 04, 2007 1:24 PM
Subject: Re: LF: CLASS D and E
> On Sun, 4 Nov 2007 12:28:05 -0000
> "hamilton mal" <[email protected]> wrote:
>
> > Hi all
> > Class D and E amplifiers are supposed to give around 80/90 %
> > efficiency. Has anyone actually achieved these figures. It seems
> > anything above 60% is hard to arrive at using normal coils/capacitors.
> >
> > 73 de Mal/G3KEV
> >
> >
> Just checked my Class-E IRF150 amp into load.
>
> At 50W output :-
>
> Dc supply = 18.7v at 3.4A
>
> Efficiency = 78%
>
> John
>
> --
> John GM4SLV
> IP90gg
> Clousta, Shetland
>
>
|
