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Re: LF: RE: 73kHz tests tonight

To: [email protected]
Subject: Re: LF: RE: 73kHz tests tonight
From: "James Moritz" <[email protected]>
Date: Tue, 12 Jun 2001 16:44:07 +0000
In-reply-to: <[email protected]>
Organization: University of Hertfordshire
Reply-to: [email protected]
Sender: <[email protected]>
Dear Andy, LF group,

What sort of TX is it?
It uses the Decca circuit configuration, together with my existing
60V PSU and modulator. It uses a single PA rather than 3 in
parallel, so the circuit is re-designed for about 2.5 times as much
current. It has 4 x STW34NB20 MOSFETs.

Only real problem so far was getting the gate driver to work - even
with both sections of a TC4427 driver IC in parallel, the drive
waveform had rather slow edges when feeding the 4 large-
geometry FETs in parallel, so I ended up adding a "booster" with a
complementary pair of discrete MOSFETs in a circuit adapted from
one of IR's application notes. The driver transformer now seems to
be the limiting factor, but is OK for the time being.
Efficiency seems to be around 90%, as we have come to expect.
The "guard" circuit seems to do it's job. Once I am sure the circuit
has a reasonable life expectancy I will post some more details.
Cheers, Jim Moritz
73 de M0BMU

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