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Bypass Resistor

Discussion in 'Electronic Basics' started by [email protected], Jul 7, 2006.

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  1. Guest

    What is the reason for putting a bypass resistor in a circuit that
    converts 3.3V to 5V and vice versa using a a bus switch (typically:
    part no.: IDTQS3861).

    A bus switch pin is connector to a external 3.3V signal pin and another
    to a 5V signal pin.
    The resistor directly connects the 3.3V signal pin to the other 5V
    signal pin?
  2. Eeyore

    Eeyore Guest

    It reduces dissipation in the 'regulator' if I've understood correctly what
    you're saying. I use the trick myself sometimes with plain 78xx regulators.

  3. yy7d6

    yy7d6 Guest

    Ayon kay Eeyore:
    What would happen when the 5V drives a HIGH signal to the line would
    the 3.3V signal be affected? btw, those two signals are I/O pins with
    different signaling, one is 3.3V and the other one is 5V so it uses a
    bus switch to 'convert' the voltages.
  4. Eeyore

    Eeyore Guest

    You're going to need to point to a schematic.

  5. Jamie

    Jamie Guest

    the only thing i can picture in my mind is the
    by pass R used in many supplies to drain off the
    caps when the power is removed.
    just a guess.
  6. yy7d6

    yy7d6 Guest

    I've found out(from the datasheet i'm referring) that the bypass
    resistor packs are NOT installed by default. They are ONLY installed
    when the FET switches(bus switch) are not installed (mutually

  7. Eeyore

    Eeyore Guest

    I seriously doubt anyone cares frankly !

  8. yy7d6

    yy7d6 Guest

    Ayon kay Eeyore:
  9. Eeyore

    Eeyore Guest

    You responded ?

    Why didn't you post a schematic somewhere ? - it might finally make some more
    sense !

  10. yy7d6

    yy7d6 Guest

  11. PeteS

    PeteS Guest

    If you read the text, you will see this highly informative note:

    "NOTE: These resistor packs are NOT installed by default. They are only
    installed when the proceeding (sic) page's FET switches are not
    installed (mutually exclusive)."

    In this particular application, one may either use the bus switch, or
    simply pass the signals through directly. Note that the resistors are
    in fact 0 ohm devices (links).

    This is a common trick - use the bus switch when there is a voltage
    domain to cross, or where it is truly necessary to translate the
    signal, and use very low cost links to pass the signal where that need
    is not present, thus saving the cost of a bus switch (an order of
    magnitude higher cost than the 0 ohm resistors).


  12. Supahi


    Sep 24, 2010
    In a common emitter small signal pre-amplifier negative feedback is from base bias resistor to a part of emitter resistor. The other part of emitter resistor is bypassed by a large condenser. Closed loop voltage gain is kept at 20. What is the ratio between bypass resistor to non-bypass resistor (if it is 220 ohm)?
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