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  • seven segment LED

    theta

    theta

    @theta-VLpGrb
    Updated: Oct 22, 2024
    Views: 858
    I need help with this--

    Calculate the maximum power used by a three-and a half digit seven segment LED display with a 5v supply and a 10ma LED current. Also detremine the power dissipated in each LED series resistor if the LEDs hv Vf=1.4V.

    Can someone plz solve it??
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Replies

  • reachrkata

    Member • Oct 25, 2009

    Before we go to the actual solution, lets see if people can get the answers first -

    a) Max power used = 1.15W
    b) LED resistor power = 36mW

    - Karthik
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  • theta

    Member • Oct 26, 2009

    I have no clue about this 3 and a half digit part. I studied the seven segment display but did not find the 3 and a half digit part of it.
    Can someone please explain what this 3 and a half digit is first??
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  • theta

    Member • Oct 29, 2009

    Someone please help. This is urgent!!!
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  • reachrkata

    Member • Oct 31, 2009

    Though i am not completely sure about it, i think the half digit means that in the Most Significant digit position, all the segments will not be turned on. The logic will be implemented such that the MSD can be either 0 (no segment glows) or 1 (two rightmost segments glow).

    - Karthik
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  • theta

    Member • Nov 5, 2009

    I have got the first part, i.e. the maximum power dissipated. Its 5*10*23=1.15W. 23 for the 23 segments of the 3 and a half digits of the 7 segment LED display.
    But how is the 2nd part solved??
    Please explain, this is very important.

    Thanks...
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  • reachrkata

    Member • Nov 6, 2009

    Simple -
    Given that Power supply is 5V, and LED Vf is 1.4V. The rest of the voltage has to drop in a resistor. Secondly current required is 10mA

    Therefore R = (5-1.4)/10mA = 360 Ohm

    Resistor Power = I^2*R = 10mA*10mA*360 Ohm = 36mW

    -Karthik
    😁
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  • theta

    Member • Nov 9, 2009

    Thank you very much for the help. Cheers!!!
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