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output current of 74HC595 shift register
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output current of 74HC595 shift register

by EEdy on Wed Oct 09, 2013 6:38 pm

hi i am working on a project that requires 4 74HC595 shift registers daisy chained together and each register will have 8 LED connected to it.
according to the datasheet of 74HC595, the max current is 70mA, but one LED sources 20mA current so

does it mean I can only light up no more than 3 LEDs at once?? I purchased a SpokePOV kit before, and i know that it can display a pac image, i have never tried it personally. To display a pac, you need to lit up all LEDs, i am just wondering how you manage to light them all up at once without burning the shift register

Thanks
EEdy
 
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Re: output current of 74HC595 shift register

by adafruit_support_rick on Thu Oct 10, 2013 7:46 am

The SpokePOV uses the 74LS595N, which can supply higher currents to the output pins than the 74HC595.
Also, the SpokePOV uses resistors to bring the current per LED down to 10mA.

Design notes and schematic are here:
http://www.ladyada.net/make/spokepov/hardware.html

adafruit_support_rick
 
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