Neon indicator power problem

Discussion in 'General Electronics Chat' started by magnet18, Jan 22, 2011.

  1. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Hi all,
    i recently got some neon indicators, in-3 type, and am experimenting with powering them
    They are rated for 90-110V @ 1.3mA
    i thought the circuit i created would create a voltage divider to put it in that range when the pot is at max resistance
    the tube is lighting but the pot is taking a drop of 130V, and the indicator is only getting 45V
    Also, im measuring approximately 8mA of current to the indicator, and am unsure how to limit this though i am sure it is probably simple I=E/R stuff

    Thanks for any help, im sure this is probably just my incompetence
     
  2. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
    1,232
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    heres the schematic, sorry it didnt upload the first time
     
  3. eblc1388

    Senior Member

    Nov 28, 2008
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    Neon indicator is of gas discharge type and does not follow Ohm's Law exactly. They take no current when off and requires some 70V or higher to fire. Then their terminal voltage drops to 40~50V.

    They are extremely easy to use by just placing a current limiting resistor in series to limit the current.

    When they lights, their terminal voltage can be as low as 40V as you have found out.

    So the math to calculate the current limiting resistor is drive AC voltage - 40V and divides by the intended current.

    (180 - 40) / 1.3mA = 107K

    Any resistor with value from 100K to 120K will do nicely.
     
    magnet18 likes this.
  4. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Thanks for the help :)
    I was actually using dc, sorry i forgot to mention that but i doubt it makes much difference...
    (i have no symbol for a dc-dc converter :( )
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
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    The above calculation would work with voltages of dc or AC rms.
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The only difference as far as neon bulbs go is that only one element lights up with DC, whereas AC lights up both.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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  8. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Thanks for the links Bill, those are interesting circuits.
     
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