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Re: LF: VLF exciter

To: [email protected]
Subject: Re: LF: VLF exciter
From: wolf_dl4yhf <[email protected]>
Date: Sun, 29 Dec 2013 18:09:05 +0100
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Hi Stefan,

> Hmm, P ~ 300W? :-)

Not really... the design goal was driving the PA with the 13.8 V, "20 ampere" power supply. There actually is some stray inductance (despite using 17 mm wide copper foil) so the load "seen" by the drains is a bit higher than 12 V / 20 A = 0.6 Ohm. The max DC input current is now about 15 A, but that's ok for me. Also, after adding the first lowpass (which transforms from 12.5 to 50 Ohms, at very 'moderate' RF currents), the waveform at the drains isn't such a nice square wave but the HUF75343 can 'absorb' the very narrow spikes (80 ns long, and over 55 V) when none of the two FETs conduct for a very short time. According to the datasheet (where the FET are mistreated by driving an inductive load, as a test) they should survive this, even without an RC snubber network or an extra Zener diode. I will find out soon - also if P ~ 150 W is enough to reach 1 W ERP. From experience with the old PA (in which the FETs were biased into 'almost linear operation', at the expense of efficiency), it should be possible.

  Wolf .

An alternative to the foil could be: 4x;ARTICLE=57209;SEARCH=CLI 200/120
73, Stefan

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