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Re: LF: component replacements

To: [email protected]
Subject: Re: LF: component replacements
From: "Hans-Albrecht Haffa" <[email protected]>
Date: Sat, 20 Mar 2004 21:20:16 +0100
Organization: http://freemail.web.de/
Reply-to: [email protected]
Sender: [email protected]
Dear Dick,
here a short anwer to Your questions.
55, Hans-Albrecht
DK 8 ND

[email protected] 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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