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Phone Line In-Use LED

Discussion in 'General Electronics' started by Rich Grise, Nov 25, 2003.

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  1. Rich Grise

    Rich Grise Guest

  2. The Ttranszorb is a good idea. But what is it? What is its specs?

    Other Qs are:

    You gave no value for the "R?" in the input wire. it should be the
    same as the other R1, 100k, so that the line stays balanced.

    Why is the tranzorb _after_ the 2 resistors and bridge? I would think
    it should be before, to protect those components.

    My thought is that by the time the fault voltage gets high enough to
    cause the tranzorb to do its job, it has already caused damage to the
    LM393 and other components.

    I would include two clamping diodes after R5, to the + amd - power
    supply. It's also a good idea to put two diodes anti-parallel across
    pins 2 and 3 of the LM393 to prevent overvoltage. These are some of
    the ways we used to protect the line driver boxes we used all over
    campus. Believe me, when a lightning storm comes by, you will need as
    much protection as you can get to keep your phone line-connected
    equipment running.

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