# 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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125
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
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125
heres the schematic, sorry it didnt upload the first time

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56.5 KB
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3. ### eblc1388 AAC Fanatic!

Nov 28, 2008
1,543
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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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125
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 AAC Fanatic!

Nov 28, 2008
1,543
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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.

Mar 24, 2008
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8. ### magnet18 Thread Starter Senior Member

Dec 22, 2010
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125
Thanks for the links Bill, those are interesting circuits.