Need Some Suggestions

Discussion in 'The Projects Forum' started by Hobby_Guy, Jan 3, 2008.

  1. Hobby_Guy

    Thread Starter New Member

    Jan 3, 2008
    3
    0
    I could use some suggestions/ideas...

    I'm currently using a PIC to control the backlight on an LCD. The backlight is a typical LED backlight used in many LCD's. Currently, I'm controlling the intensity of the backlight with pulse width modulation from the PIC and it works just fine. BUT, the intensity (brightness) is limited by the ability of the PIC to ouput only 25mA. The backlight wants to see 160mA.

    I thought about using a relay, but that would only give me two levels of brightness (using a DTDP relay).

    So, any ideas?

    Thanks
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    You can drive a transistor through a resistor, with PWM from your PIC to drive the backlight LEDs at a higher current. Is 160mA the maximum peak, or maximum continuous current for the LED's? Do you have a link to the data sheet?

    Ken
     
  3. Hobby_Guy

    Thread Starter New Member

    Jan 3, 2008
    3
    0
    Ken, Thank you for responding.

    The 160mA is "Typical", per the drawing. Voltage ranges from 4.2 to 4.6. Using PWM, I measure the voltage, which varies from 0 to about 4.

    The part is from Digikey (part # 67-1759-ND) It's a two page drawing - the following is a link to one page.

    Do you have a recommended resistor value, transistor and hook-up scheme?

    www.lumex.com/pdf/LCM-S01602DSF+B-page2.pdf

    Thanks again,
    bruce
     
  4. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    You can use a diode and a logic level FET to do this,

    check out Dallas Semi's "Application Note 163-Using DS1050 Programmable PWMs to Control a DC Motor and an LCD LED Backlight"

    http://www.maxim-ic.com/appnotes.cfm/an_pk/163

    Steve
     
  5. Hobby_Guy

    Thread Starter New Member

    Jan 3, 2008
    3
    0
    Perfect!

    Thanks, Steve

    bruce
     
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