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Transistors for simple switching circuits

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  • k2wr
    Of the transistors mentioned for switching CW, PTT, FSK, etc., I think the 2N2222 (these days you ll really get a 2N2222A) is a superior choice to the
    Message 1 of 1 , Aug 25, 2011
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      Of the transistors mentioned for switching CW, PTT, FSK, etc., I think the 2N2222 (these days you'll really get a 2N2222A) is a superior choice to the 2N3904/5/6. First of all, it's an NPN (like the 3904) so you can use the open collector / common emitter configuration rather than a common base circuit that you would have to use with a PNP (when switching a positive voltage), but of more significance, the Vceo of the 2N2222A is a little higher (75v) and the maximum collector current is a lot higher (600 ma) than the other series. None of this is important if you're switching a 5v CW keying line, as is common in a modern solid-state radio, but when switching PTT lines, particularly if an amplifier is involved, you do have to pay attention to the open-circuit voltage and the amount of current you're going to sink.
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