Message-ID: <000801c44d59$ede5b960$bc0c97d4@oemcomputer>
From: "Johan Bodin" <jbodin@tele2.se>
To: rsgb_lf_group@blacksheep.org
References: <6.1.0.6.2.20040608100555.02801340@POP3.freeler.nl>
Date: Tue, 8 Jun 2004 13:09:32 -0000
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Subject: LF: Re: Effect of LP-filter om efficiency (shorter...)
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Dick,

just a few more comments,

you wrote:

> So it seems to me that class D and E amplifiers should preferably be 
> followed by a low pass filter with a series inductor at the transmitter side.

In the case of voltage switching class D and class E, I prefer to view
the series resonant tank as an integral part of the amplifier.
With such a tank in place, the output signal is already sinusoidal, with
just a litlle bit of harmonics, and you can put any kind of lowpass filter
after the tank without problems.


Another thought on the small coil in the middle of the totem-poles in
the Decca design:

In addition to Andy's explanation that the coil will limit shoot-through spikes,
I believe it also helps to reduce loss, when driving reactive loads, by throwing
the external (and fast) catch diodes into conduction before the internal (and
slow) MOSFET diodes and keep it that way until the other MOSFET turns on.
The small "kickback" from the coil will put higher voltage across the external
diode and the MOSFET diode will hopefully never start conducting.
As soon as the other MOSFET turns on, it will shunt the diode(s) anyway
since MOSFETs conduct almost equally well in both directions.


73
Johan SM6LKM