LM3914 Load capacity on output pins

Thread Starter

jj_alukkas

Joined Jan 8, 2009
753
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 :)
 

bribri

Joined Feb 20, 2011
143
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.
 

Thread Starter

jj_alukkas

Joined Jan 8, 2009
753
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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