inverter circuit for computer light

[jonjacob]

I bought a cold cathode light kit for the inside of my computer and I wanted to make a circuit that would turn the light off when the Hard Drive LED on the front of my computer case turned on.

I tried making the following circuit, but it did not work. I don't know very much about electronics or making circuits, and I did go to my library and do research which though interesting, did not help me in making this circuit work.

The cathode light runs off of 12V that comes out of the computer power supply and I think that the Hard Drive LED runs off of 5 or 6 Volts (I'm not sure exactly because I can't find my notes right now)

I've tried using PNP and NPN transistors.

If anyone can help me, I'd really appreciate it.

Here is a link to my diagram

http://www.geocities.com/bwrogaa/index.html

 

[jonjacob]

Hard Drive Light Voltage

The Voltage for the Hard Drive LED is 2V

 

[nettron1000]

The circuit wont work as shown in your diagram. The CC light should be placed in series with the transistor. The transistor is acting as a switch.

 

[tansis]

"Cold Cathode" lights operate at around 120volt,

you can switch the power supply on and off to the inverter with a transistor
or it can be perminantly powered up and the high voltage output to the tube switched with an optically isolated triac.
this is an ugly link and will look for a better schematic,
**broken link removed**

 

[nettron1000]

Cold Cathode" operates at around 120volt

Are you sure Tansis ? thought the voltage was alot higher than that, something like 300 V or so, depending on the length or something other.

 

[tansis]

I guess there are many factors involved and have yet to find any specific makers figures, but this is a good theory of operation link
**broken link removed**

 

[pike]

So you want you lights to flicker on and off with your harddrive lights??

Use a comparator to fire a mosfet or something. I tried upgrading my HDD lights with a brighter one, but it wouldn't light thanks to insuficient voltage.

mmm...300v passes my test for a stun gun...

 

[jonjacob]

Actually, I don't want the cold cathode light to turn on when the Hard Drive LED turns on, I want the cold cathode light to turn off when the hard drive LED turns on. What I was thinking was that when the HD LED turns on it would switch the transistor on. Since the path through the transistor would offer less resistance than the path through the cold cathode light, the current would bypass the light. Then when the HD LED turned off, the transistor would turn off and the current would have to go through the cold cathode.

When I tried setting this up, the Cold Cathode light just stayed on no matter what the HD LED did.

As a side note, I did try putting the cold cathode light in series with the transistor just to see if I could get the transistor to do anything, and it did sortof work, but when the HD LED turned on and the transistor turned on the cold cathode light never did get as bright as it does when just plugged into the computer normally. And when the transistor turned off, the cold cathode was still on, even though it was much dimmer than it was when the transistor was on.

 

[pike]

yeah, like i said the comparator is the answer. If you want the CCFL off when the HDD light is up, just simply swap the comparator inputs.

 

[jonjacob]

What is a comparator? Is it a chip you buy at radio shack, or is it a circuit you have to make?

Also, I guess the circuit I described above isn't really an inverter, right?