Message-ID: <18596.200012191800@gemini>
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Organization: University of Hertfordshire
To: rsgb_lf_group@blacksheep.org
Date: Tue, 19 Dec 2000 18:03:36 +0000
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Subject: LF: Guard circuit
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Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

Dear Andy, LF group,

To a reasonable approximation, the voltages in the tank circuit, and 
the guard circuit, will vary in direct proportion to the supply volts for 
a given value of load impedance. This should hold provided the 
forward voltage drop of the guard circuit diodes, and the voltage 
drop across the "on" Mosfets is much smaller than the supply 
voltage. So the guard circuit will operate at a particular impedance 
level, rather than a particular power/current/voltage level as with 
most overload protection.

So one way to experiment with this type of circuit whilst minimising 
explosions would be to run the amp at a much lower supply voltage, 
say 34V - reducing the energy and power dissipation everywhere 
by a couple of orders of magnitude. Of course, in a circuit full of 
non-linear components, waveforms (eg. gate drive) will change a 
bit, and adjustments are bound to be needed when the full supply is 
restored, but it should be a good starting point. You could use 
cheaper low voltage components for the initial experiments, too.

Cheers, Jim Moritz
73 de M0BMU