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Re: LF: Class E PA

To: LineOne <rsgb_lf_gr[email protected]>
Subject: Re: LF: Class E PA
From: Andy Talbot <[email protected]>
Date: Mon, 8 Oct 2018 22:23:05 +0100
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That's a very good point for all Class-E designs, at any frequency.  They only work because the drain voltage / current is so carefully tuned and setup when operational generatign RF.   Upsetting that state by turning the drive off and on is not going to be good.

Time to revisit that big 50V PWM arrangement



On Mon, 8 Oct 2018 at 22:19, David Bowman <[email protected]> wrote:
Hi Tom.

If it helps, I believe nearly all broadcast transmitters keep the drive running and then key the supply to the many paralleled FETs in the PA.
Of course, that also is a neat way of applying AM as pulse width modulation......but I'm sure it will be fine for your system of modulation too.

73

David

On Sun, Oct 7, 2018 at 5:52 PM DK1IS <[email protected]> wrote:

Hello Group,

Planning a new single-ended Class E PA for my activities on the Dreamers Band (8.27 kHz) two questions came up - perhaps someone can help me:

-  Being interested only in on-off-keying I´m concerned about the capacitor in parallel to the power FET which in my case on VLF will be in the uF range. If the DC supply is on and without gate drive this capacitor is charged to the DC supply voltage. At the first positive gate pulse it discharges via the drain-source-path, the current being  limited only by parasitc impedances - a poorly defined condition which usually has to be avoided. Does this mean that I have to apply drive continously and key the DC power supply only, perhaps synchronously to the next positive drive pulse?
 
Is there any rule of thumb for the inductance of the rf choke in the drain-power supply path?

Thanks for any idea!

73,
Tom, DK1IS
www.qrz.com/db/dk1is

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