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Split Voltage for Driver IC & Backlight

Discussion in 'General Electronics Discussion' started by AGS, Nov 3, 2015.

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  1. AGS

    AGS

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    Nov 2, 2015
    Let me start out by saying that I know very little about electronics.

    I have an LCD module that displays time/temp and has a backlight. The backlight requires 3V whereas the driver IC only requires 1.5V. The power source is 2xAA batteries. There are 4 pins - 1&2 for backlight and 3&4 for IC. What are my options to connect the backlight and driver IC to the power source so that they both function properly? What's the most efficient option?

    The backlight works when connecting 3V to pins 1, 2, 3, 4 but the time/temp is stuck on full display.

    The time/temp display works when connecting 1.5V to pins 1&2 or 3&4 but backlight doesn't work.

    Connected 3V to pins 1&2 and a separate 1xAA battery to pins 3&4 - backlight worked, time/temp stuck on full display, and 1xAA battery popped.

    LCD Drawing and Driver IC schematic are attached. The LCD manufacturer provided a markup schematic of the driver IC for how to split the voltage but it's over my head. Can anyone help explain?
     

    Attached Files:

  2. AnalogKid

    AnalogKid

    2,515
    718
    Jun 10, 2015
    My guess is that you can do this with two 1.5 V AA cells in series. Picture them stacked vertically, the -end of the upper battery connected to the + end of the lower battery.

    Lower battery - terminal is system ground, connected to device pins 2 and 4.
    The center battery +/- connection is the + output to device pin 3.
    The upper battery + terminal is the LED power to device pin 1.

    ak
     
    BobK likes this.
  3. AGS

    AGS

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    0
    Nov 2, 2015
    Thanks for the reply ak. Can you please explain some of the reasoning behind your solution? What voltage does this supply to the backlight (pins 1,2) and the driver IC (pins 3,4)?
     
  4. AGS

    AGS

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    Nov 2, 2015
    Would a voltage divider or voltage regulator work? Would one be more efficient than the other?
     
  5. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    No need, Analog Kid already gave you the simplest solution. It will supply 3V to the backlight and 1.5V to the driver.

    Theoretically, both batteries would by supplying the back light and only one supplying the driver, so you might think that one would run down faster than the other, but the current for the driver is probably so small that it can be neglected compared to the backlight.

    Bob
     
  6. AGS

    AGS

    4
    0
    Nov 2, 2015
    The LCD manufacturer recommended that I add the U2 and LDO components in the attached to split the voltage with stable voltage and low power consumption/heat dissipation. They recommended that I not connect 2xAA's in series due to different power consumption. Just looking for confirmation of which is the best solution.
     

    Attached Files:

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