Posted for Jeff Peterson
<jeffreyb.peterson@gmail.com>:
Hamid Wasti wrote (referring to this http://www.barkeraircraft.com/files/AOA_rDisplay.pdf
) study the circuit on page 6, you will see that the LEDs are connected to the "+14V In" input voltage and they are set up
to run at 24mA not the "typical 10mA" that you pulled out of thin air. At 13.8V input and a drop of 2.2V on the LEDs, the chip has
to dissipate 11.6V at 24mA or 278mW. At a Theta-J-A of 55C/W, this leads to a 15C increase per LED that is actually on. I
can verify that this is real error in the circuit, since I burned up an LM3914 using a similar schematic. It should solve
the problem to add a series resistor for each LED. This will reduce the voltage across the LM3914 and keep its temp
within limits. Or use multiple LEDs in series and make light rather than heat. By the way, we all could benefit
from everyone trying to make more light than heat...please?! Cheers, -- Jeff
Peterson
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