Date: Sat, 20 Mar 2004 21:20:16 +0100
Message-Id: <200403202020.i2KKKFQ16097@mailgate5.cinetic.de>
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From: "Hans-Albrecht Haffa" <dk8nd@web.de>
To: rsgb_lf_group@blacksheep.org
Organization: http://freemail.web.de/
Subject: Re: LF: component replacements
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Dear Dick,
here a short anwer to Your questions.
 55, Hans-Albrecht
DK 8 ND

rsgb_lf_group@blacksheep.org schrieb am 20.03.04 19:54:09:
> 
> Hello all,
> 
> I'm not an expert in all the special types of components
> around, so therefore some questions here.
> 
> In several transmitter designs I found a skottky diode MBR150
> in the gates of the FET's.
> As I don't have them here (yet?) I was wondering if these can be
> replaced by other types of (schottky) diodes.
> 
> First question: the MBR150 is a 50V/1A type. Can I use types
> with higher currents, and how important is the voltage rated?  

Diodes with higher current rating have a fairly lower forward drop voltage.  You nearly allways can use diodes with higer current rating.  I dont know the purpose of these diodes at the gate of the FETs and I have yet not seen them in this place. 

> 
> Second question: as fas as I understand schottky diodes are extremly fast,
> but what about the use of so called 'very fast soft-recovery
> avalanche'diodes,
> like the BYV26 or BYV 28 with Trr of 25ns?
> I have plenty of them in my junkbox, but really no idea whether these are
> fast and/or usable for this purpose.

Diodes with a Trr of 25 ns are fast for switch mode power supplies. Schottky-Diodes are faster. But these components have a pretty high capacity and can be build only for voltages up to 80 V as single diode components.  BYV26...2 are very good components for HF. 


> 
> Finally an question about David, G0MRF's 300W transmitter (actually should
> ask it
> David personally......) that one uses an H11L1 optocoupler with
> schmitt-trigger output
> in it's protection circuit.
> Wonder if that one can be replaced by a normal transistor type output
> optocoupler.
> 
> It is a bit frustrating to find some components so hard to find here in
> Holland.......
> Some designs seem to use several "exotic" components which make it rather
> difficult to build them right away.......
> 
> 73 Dick, pa4vhf
> 
> 


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