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Date: Sun, 4 Nov 2007 16:57:28 +0000
From: "Andy Talbot" <andy.g4jnt@googlemail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Re: CLASS D and E
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In my 700 Watt direct-from mains transmitter
http://www.scrbg.org/g4jnt/137tx.pdf
efficiency came out somewhere between 80 to 90%.  As Jim says, its
difficult to measure accurately   At one point, due to measurement
errors, the calculated efficiency ended up at 105%.

Andy  G4JNT



On 04/11/2007, James Moritz <james.moritz@btopenworld.com> wrote:
> Dear Mal, LF Group,
>
>
> > 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
> >
>
> Certainly you should be getting better than 80% for a reasonable class D or
> E design at LF or MF. I find about 90% is typical for a "good" design - it
> is actually quite hard to get an accurate figure due to the small difference
> between DC input and RF output powers.
>
> In my designs I have used silver-mica or polypropylene capacitors, which
> have very low losses at these frequencies. For inductors, I have used
> air-wound coils and Micrometals -2 mix iron-dust toroid cores - the rule
> here is if doesen't get excessively hot with the key down, the power loss is
> probably ok! For most class D and E designs, which have quite low loaded-Q
> tank circuits (<5, say) an inductor Q of 100 or more is probably adequate
> and fairly easy to achieve. If you want to use a high loaded-Q tank circuit,
> it might be another story...
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>