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Negative voltage, contrast and display

Discussion in 'Electronic Design' started by pozz, May 9, 2005.

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  1. pozz

    pozz Guest

    Hi all,

    can someone tell me what is the technique used in the display
    to adjust the contrast? Normally there's a negative voltage
    to make that but what happens when that voltage changes?
    Why a negative voltage is necessary?

    I want to study the display technology. Can someone tell me
    some tutorial or web site with a lot of informations about
    this subject?
     
  2. Rich Grise

    Rich Grise Guest

    Well, here's a couple of places that you can start at...

    Ah, Schtool! After a search at
    http://www.howstuffworks.com/search.php , they leave the URL
    in the window, unlike google. I did a search on "cathode-ray
    tube" (without the quotes) and on "CRT display" (also without
    the quotes) and a lot of the links that showed up sound like
    a very good introduction to CRT principles.

    The short answer is that they use a negative voltage because
    it's a "tube". The electrons boil off of the cathode, and are
    attracted to the anode(s), just like any tube, but they have
    focusing (focussing?) electrodes to make a beam; but generally,
    the control grid will be more negative than the cathode, to
    regulate the rate of flow of electrons. This will have a DC
    bias, which sets the "brightness", or "intensity" level, and
    a control signal (the "video") which changes the intensity
    very quickly as the electron beam is scanned across the screen.

    The "contrast" control actually controls the gain of the video
    amplifier - more variations in control grid voltage give more
    variations in intensity of the "flying spot".

    Hope This Helps!
    Rich
     
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