Scanner Lamp Voltage

Discussion in 'General Electronics Chat' started by ALT2016, May 8, 2008.

  1. ALT2016

    Thread Starter New Member

    Feb 13, 2007
    I am messing around with some back-light project for my TV and found an old flatbed scanner lamp in my junk box. Hoping to use this lamp, I have tried to convince it to glow but no luck yet.

    I tried from 3V to 12V DC from an adjustable power supply and nothing works. After doing some reading, it looks like I might need some form of inverter/driver or something to make it work. I couldn't get any clear indication but if I understand correctly, I'll need about 40V DC (current unknown). Would this be a "generic" voltage or will it differ from lamp to lamp?

    Can anybody confirm what voltage, AC or DC, and what current is needed to make it work? Also, if special circuitry is needed, a schematic would be very helpful.

    The lamp is about 25cm long an 4cm thick with a gray rubber cap on each end. I found no markings anywhere on the lamp. It's not much but I hope it helps.
  2. SgtWookie


    Jul 17, 2007
    Might be a CCFL (cold cathode flourescent). These can require a fairly high voltage to light them off (150-450) and then a lower voltage (regulated by current) to sustain the ionization.

    Without knowing what the tube's rating is, it would be somewhat problematic to come up with values that won't shorten the life of the CCFL.

    Also, there's the problem of dealing with high voltage. Unless you've been spending a good deal of time with electronic/electrical circuits, I suggest that working with high voltage is something you could put off for a while.

    But if you're really determined to experiment, you could have a look at this page:

    It's a high-voltage flyback circuit. You would need to modify it so that it was regulated by current rather than by voltage. However, it's a good starting place; and the page is a very good tutorial on flybacks.
  3. ALT2016

    Thread Starter New Member

    Feb 13, 2007
    Thanks Sgt. I'll take a look at the link for future reference but those voltages make me a bit nervous.

    I've done some more digging and came across the circuit where I butchered the lamp from. It seems at some stage I also removed two transistors from this circuit for some other nefarious project I was working on. Problem is - I don't recall what the values of these transistors were. Searching for details on the specific board came up blank. I took a photo of the front and back hoping somebody might be able to identify or advise. I can provide a larger image if needed - just thought I'd reduce it a bit for quicker loading.

    Q1 and Q2 are the two missing components.