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Cold Cathode CFL.

Discussion in 'Lighting' started by Clive Mitchell, May 21, 2006.

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  1. Remember we said that he first person to get a cold cathode compact
    fluorescent lamp would sacrifice it for the betterment of the group?

    Here it is...

    http://www.emanator.demon.co.uk/cclamp.jpg

    Not much to write home about.... The VERY simplified schematic doodled
    in the picture shows that it's basically a standard CFL circuit, but
    using a step up transformer instead of the choke. This lamp in
    particular is notable for the complete lack of suppression components
    and no electrolytic capacitor.

    The lamp is quite noisy in operation and as you would expect with the
    lack of smoothing you get a 100Hz (50Hz) buzz with a relatively high
    pitched squeak superimposed.

    I guess the lack of an electrolytic to dry out is good, but the
    conventional transformer for driving such a long thin tube is a bit
    dubious from a winding insulation perspective.
     
  2. The efficacy is lower without the electrolytic capacitor
    since the HF is then highly modulated at 100 Hz.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  3. However, it probably has a power factor of 1, and it should
    be dimmable with a regular cheap dimmer (providing you have
    enough of them to reach the dimmer's minimum power rating).

    Clive, what is the make and power rating, and where did
    you get it? Looks like it's a GU10 form factor.
     
  4. Good point. In hindsight the circuitry is closer to an electronic
    halogen transformer but with a somewhat different winding ratio.
    It's a Lloytron Lighting lamp for GU10 base and with a rating of 4W
    (equivalent to a 20W tungsten lamp apparently).

    Gets pretty hot on the front when in use.

    To quote:-

    10,000 hours average life.
    70 Lumens average light output.
    Suitable for use outdoors. (?)
    Not suitable for use with dimming circuits.
     
  5. Maybe it's just a blanket disclaimer left over from the hot cathode
    versions.
     
  6. Dimming is one of the advantages of cold cathode fluorescent
    lamps. However, the ballasts used with these cold cathode
    CFL may not be compatible with dimmers.

    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  7. Hard to tell. Perhaps they think the 150 nF capacitor will
    draw large enough current spikes to damage the dimmer. Or,
    similar to what Clive has said, they are so used to warning
    against using their lamps on dimmers that they never
    considered that this one might be OK.

    BTW - the diagram shown in Clive's original post must be
    incomplete. The "transformer" has only two connections to
    the rest of the circuit - which would make it an inductor.
    To do any "transforming" it needs at least three leads.


    --
    Vic Roberts
    http://www.RobertsResearchInc.com
    To reply via e-mail:
    replace xxx with vdr in the Reply to: address
    or use e-mail address listed at the Web site.

    This information is provided for educational purposes only.
    It may not be used in any publication or posted on any Web
    site without written permission.
     
  8. My quick sketch was highly abbreviated, but also very weird. On the
    first scrutinisation it just didn't seem to have much connected to what
    I would have classed as the common winding of the transformer.
     
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