How current pass through floating pin?!!

Discussion in 'General Electronics Chat' started by buffon2009, Aug 23, 2014.

  1. buffon2009

    Thread Starter New Member

    Dec 7, 2011
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    Hi everybody,.

    i had puzzled for a long time and i con't convince myself that floating pin in a circuit can lead noise .. how could it come with open circuity??!!

    can the Current flow through open circuit?

    [​IMG]

    assuming the floating point of the switch and there's electromagntic fields already comes from phones,Ac,....etc

    how can the current pass through this circuit ??!!!

    as i read that floating pin can introduce noise or wark as antenna..but how come floating pin works as antenna while the antenna not closing the circuit??!!!
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Current induced by electric FIELD?
     
  3. buffon2009

    Thread Starter New Member

    Dec 7, 2011
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    0
    how current flow through open circuit??!!!
     
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    easily if there is electric FIELD to induce it
     
  5. buffon2009

    Thread Starter New Member

    Dec 7, 2011
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    could you explain more please
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    Induced current can only flow in an "open" circuit if the frequency of the induced voltage is high enough to make the capacitance reactance of the open circuit stray capacitance to ground low enough to conduct the induced current.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
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    The issue is the "floating pin" and has nothing to do with the picture posted by the OP.

    A floating pin, e.g. on an IC, is one that has no external connection to either ground or Vcc (no pull down or pull-up). Such a floating pin can have a very high input impedance, while being connected to logic inverter(s) with high gain inside the IC. A bit of stray capacitance from some external, changing logic signal can couple that signal into the floating pin, and cause it to switch through its logic threshold...

    This would be prevented if the pin was tied to either Gnd or Vss with an (pull-down or Pull-up) resistor.
     
  8. to3metalcan

    Member

    Jul 20, 2014
    228
    23
    I had a transistor switching circuit I designed for a protected power supply with a diode at the input...the gain of the switch was very high, and putting my finger near the diode when the anode wasn't connected to anything would switch the circuit on, just because I was acting as an antenna for AC line hum or whatever, and the diode was rectifying it into DC. My jaw hit the floor the first time it happened.
     
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