seven segment LED

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??

Replies

  • reachrkata
    reachrkata
    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
  • theta
    theta
    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??
  • theta
    theta
    Someone please help. This is urgent!!!
  • reachrkata
    reachrkata
    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
  • theta
    theta
    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...
  • reachrkata
    reachrkata
    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
    ๐Ÿ˜
  • theta
    theta
    Thank you very much for the help. Cheers!!!

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