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Re: LF: W1VD amp help - MY FINAL POST

from [Andy Talbot] [Permanent Link][Original]
To: LineOne <[email protected]>
Subject: Re: LF: W1VD amp help - MY FINAL POST
From: Andy Talbot <[email protected]>
Date: Mon, 23 Apr 2018 08:24:13 +0100
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The irony here is that class-E does not mandate a short sharp gate drive.  As it is tuned and adjusted for zero Drain volts at the transition, the shape of the drive is less critical.

So says Fred Raab, the guru of using low cost mosfets at HF.   It may not be quite so true for LF, but I went to a talk given by Fred many years ago on this subject, and have seen several papers by him.

However, my 400 Watt 475kHz amp does have a nice meaty driver chip.   http://www.g4jnt.com/QRO_500kHz_PA_Breadboard.pdf

(Yes I know it's the 500kHz version - somehow never got round to updating the write up after retuning for 475kHz)

Andy  G4JNT 

On 22 April 2018 at 18:23, N1BUG <[email protected]> wrote:
Since I am considering an upscaled version of my current class E
amplifier, I put that back on the bench and was taking some
measurements. It uses a single 34N20 FET. In particular I looked at
the gate waveform with the same scope, probes, and settings I've
been using with the W1VD deck. I was shocked at how steep the rise
and fall times are and how it seems to 'power through' the FET
turn-on anomaly. This stands in stark contrast to the W1VD deck with
its slow gate rise/fall and long hiccup at FET turn on. At least I
know the scope is capable of displaying a 'crisp' gate waveform. ;-)

Paul N1BUG





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