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How does a TA9687GN fluorescent backlight driver work?

Discussion in 'Electronic Repair' started by mike, Jul 3, 2013.

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  1. mike

    mike Guest

    I need an explanation of how the protection circuit works in a TA9687GN
    backlight driver.
    There are hundreds of datasheet links, but they all lead to the same
    place...not found.

    I did find a functional block diagram in a monitor manual.
    Seems that there are two thresholds related to the current sense input.
    0.7V and 1.2V. The 1.2V threshold detector connects to a "switch symbol"
    with no indication of what controls the switch or why you'd ever
    want the Isense and Vsense detector outputs hooked together and going
    nowhere else.
    ???????

    Anybody got a datasheet or an explanation of how the protection circuit
    works and what the normal waveform at Isen should look like?

    Thanks, mike
     
  2. Guest

    Mike,

    I think I found the monitor link you viewed at "http://www.go-gddq.com/upload/2011-07/11071512159125.pdf" (mind the wrap) Perhaps a similar device such as the OZ960 "http://monitor.espec.ws/files/oz960_applicationsschema_189.pdf" would shed some light on your question.

    I know these CFL drivers auto shutdown to self protect the circuit when thetubes go bad either by drawing too much current or having an over voltage condition. I believe someone in this group used a neon bulb with a bunch of resistors to simulate a CFL for use in figuring out which bulb went bad. Otherwise you must open up another monitor, pull the plug on one CFL and swap the connection till you find the bad bulb. Don't forget to check the main supply for bad caps and/or blown fuse to CFL inverter, which has been a common problem in many displays I have repaired.

    regards.
    al
     
  3. mike

    mike Guest

    Thanks,
    I was hoping for info on the specific chip.
    The thing works ok with the protection disabled.
    If I filter the Isense line, the level is smack in the middle between
    the two thresholds.
    I've tested every part in the protection circuit.
    Supply caps have low ESR and correct capacitance.
    No evidence of bad caps on the power supply leads.
    I have an inverter from a laptop that will light each of the 4 lamps.
    Just barely, so not clear that they're "good", but at least not open.

    I've found lots of backlights on Ebay, but none anywhere near this long.
    Not sure I'd be able to get one installed without breaking it anyway.
    Guess I'll use it the way it is until it dies.
    Thanks, mike

    Moving on to the next display with dead backlight...
     
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