Post by thread:[EE]: help with CCFL backlight supply circuit

Hello, I'd like to get one of these tubes up and running from junkbox parts. I have no transformer (designed for the purpose), no SCRs, and no good circuits for generating the HV. On the other hand, I do have a huge spool of some tiny magnet wire and some forms, plus some small-signal transistors, so I could put together something ugly for now. From the looks of those inverter boards, they don't consist of much more than that. I need a reasonably simple circuit, so some guidance would be most helpful. A search of the 'net was not too revealing. The tube itself is white, about 5" long, and 1/16" diameter. Single lead on each end, no other markings. Unit pulled from working equipment, which I don't have. The entire backlight is about 4" x 5". See link below. Somewhere, I saw a tube like this that required a start voltage of 1200V, running at 700V at perhaps 500Hz? That could be way off. I can afford to waste a few, so I'd like to err on the high side and cut it down from there. These are freebies from a friend, thirty in total. Will share some for the first junkbox-grade supply circuit that works. One thing I do know - holding one end in my hand, and the other to a television screen will cause brief flashes. http://www.rof.net/yp/alphaone/ccfl.jpg TIA, JB -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> I'd like to get one of these tubes up and running from junkbox parts. I have > no transformer (designed for the purpose), no SCRs, and no good circuits for > generating the HV. On the other hand, I do have a huge spool of some tiny > magnet wire and some forms, plus some small-signal transistors, so I could > put together something ugly for now. From the looks of those inverter > boards, they don't consist of much more than that. I need a reasonably > simple circuit, so some guidance would be most helpful. A search of the 'net > was not too revealing. Fluorescent tubes are really current devices. They need a high voltage to get going initially. Once the mercury vapor is exited, the resitance drops dramatically. You need to find specs for the starting voltage and the operating current. If you don't have specs for your tubes, look up the specs for tubes of similar length and diameter as starting points. The parameters are mostly a function of the tube geometry because most tubes use pretty much the same mercury vapor inside. Note that small two terminal tubes are different from the large 4 terminal tubes. These larger tubes have heated cathodes. ***************************************************************** Olin Lathrop, embedded systems consultant in Devens Massachusetts (978) 772-3129, spam_OUTolinTakeThisOuTembedinc.com, http://www.embedinc.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

So - similar to a HeNe laser tube, except AC instead of DC? Like I noted in my original message, the only specs I have seen were for a tube of similar size, and they suggested 1200V starting, and 700 running at 5mA. I'm guessing that in a pinch, one could use a large value, high-wattage resistor to limit the current on the HV side. I did eventually find some inverter circuits here that may work: http://www.repairfaq.org/REPAIR/F_samschem.html#SAMSCHEM_008 JB > {Original Message removed}