LM3914 Load capacity on output pins

Discussion in 'The Projects Forum' started by jj_alukkas, Mar 8, 2011.

  1. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    Im building a simple audio spectrum indicator using an LM3914 chip. I dont need it to be too complex, so Im using only one chip with a filter and driving 7 led's per output pin. After a detailed understanding of the datasheet, I came to know it can give the same voltage on the output pins as Vcc and a maximum 30mA current per pin. If I put 7 led's per pin in series and use 5 pins only, so 7x5=35leds, will I be able to run all led strings without overheating the chip or dimming the leds as more led's light up? The chip will be operating in bar mode, so almost all will be lit up at peak levels. so 1.8x7=12.6v is needed on each output pin and I'll give 15mA current. Is it safe? Or do i need to use a transistor driver per pin? I will be using red, green and yellow led's. I just need help regarding the driving part. Please advise. Thank you in advance :)
     
  2. bribri

    Member

    Feb 20, 2011
    133
    5
    35 leds (and in bar mode) sounds like a bit too much to me.
    but something like five 2n3906's and some resistors might do the trick.
     
  3. jj_alukkas

    Thread Starter Well-Known Member

    Jan 8, 2009
    751
    5
    Thanks for the reply, but that'll be too bulky for my application, so can u tell me if a BC547/557 can do the trick ? load is 15ma at 12.5v so will it?
     
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