purpose of a component in a circuit

Discussion in 'General Electronics Chat' started by Mike Anderson, Mar 31, 2012.

  1. Mike Anderson

    Thread Starter New Member

    Mar 31, 2012
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  2. BSomer

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    Dec 28, 2011
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    I believe that is the shunt resistor. It is used in conjunction with the current meter so that the meter shows the correct current. I am not entirely certain how it works, but that is what it is used for.
     
  3. paulktreg

    Distinguished Member

    Jun 2, 2008
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    It certainly isn't a shunt resistor. ;)

    A shunt resistor goes across a meter.

    I personally don't see the need for R3. In the scheme of things 0.1R~0.33R isn't much when in series with 11R of Nichrome wire.
     
  4. BSomer

    Member

    Dec 28, 2011
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    oops... my bad.
    I looked at the schematic again and noticed that the resistor doesn't go across the meter, which is what shunt resistors do.
     
  5. Mike Anderson

    Thread Starter New Member

    Mar 31, 2012
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    could the resister be there to "drag" down the minimum voltage from the LM350K to allow a lower current through a shorter length of wire
     
  6. KJ6EAD

    Senior Member

    Apr 30, 2011
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    It seems to be a current sense resistor without any sensor. It may have been included to allow current measurement with a voltmeter during development and left in the schematic as an oversight. If one were using an analog meter movement with a lower current rating, it would make sense to use a low value shunt resistor to increase the range but obviously it's not shown in that configuration.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    My thought is a safety circuit. In the event of a major short the circuit will survive.
     
  8. Mike Anderson

    Thread Starter New Member

    Mar 31, 2012
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    if for circuit protection could the resistors be replaced with a couple of diodes each of (say) 3 amps....?
     
  9. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Seems unnecessary as a current limiting safety element, since the LM350K has internal current and thermal limiting. Seems more like a series resistor to measure current by sensing the voltage drop...if you didn't install the meter.

    Ken
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Diodes do not limit current. Neither do LEDs. All they do is smoke.

    The resistors in question do set a maximum surge value. That is the only thing they can do.
     
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