[TRLog] Need help with Keying/PTT/Paddle interface

[Nick Kennedy]

Date: Monday, January 25, 1999 11:07 AM
Subject: RE: [TRLog] Need help with Keying/PTT/Paddle interface


>
>> Good point - the darlington adds one diode drop to
>> the Vce saturation voltage! Exactly how low do the
>> modern transceivers need to go anyway? One would think
>> that pulling them down to 1 volt would do the trick.


I don't think a darlington adds a drop to Vce, it would add one diode drop
to Vbe.  In a darlington, two base-emitter junctions are in series but there
is nothing in series with the "main" collector-emitter junction.

If you're pulling voltage down low enough for a TTL logic zero, or if you're
turning off a transistor, you need to go a lot lower than 1 volt.  Maybe a
couple of tenths ...

73,

Nick, WA5BDU


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