74HC595 shift register pin current

Other Hardware LEDs and Multiplexing
1

Hi, I am planning to drive 1 Digit LED with a 74HC595 shift register. How much current can each pin provide? Thanks!

2

The datasheet will tell you. Google is your friend there.

Somewhere between 0 and 40mA-ish.

3

There are two limits: the per-pin limit (which I have seen quoted at 25mA or 35mA - see datasheet) and the total Vcc or ground current (70mA). So if you use all 8 outputs to drive LEDs, you are limited to about 9mA per pin.

4

oh dam so when displaying an "8" on the 7 Seg LED I will be in trouble :(...any other shift register that can output total Vcc current of about 160 mA?

5

so on sparkfun I found TPIC6B595 that can output 150mA continuous. The only question I have is that will it be the same setup as 74HC595 because this is the first time I will be putting this together by reading the tutorial on the website. Thanks

6

That chip looks good for the job, if a little expensive. At 150mA per pin with all pins enabled, its current rating is well beyond what you need. SRCK is the main clock pin and RCK is the latch pin. The ~G pin should be connected to ground.

7

If you can get hold of them, the MBI5168 chips are nice. About 1$ per piece, integrated current regulation too :wink:

8

btw how many LED displays are you planning to drive, and how many Arduino pins can you spare? You can drive a single 7-seg LED display direct (with series resistors) from 7 Arduino pins. You can drive 4 displays using 11 pins and 4 transistors, and 4 of those pins can sometimes be used for multiplexing input devices as well.

9

Thanks guys, I will be driving two 7-Segment 1 Digit LED's from atmega382p on PCB. The reason I want to use the shift register is because I will have to run long cables from the 328p to the LED's so I am trying to minimize the amount of cable I have to run. With Shift register I only need to run 5 cables.

10

This one would be good in place of 74HC595

Or add this to output of 74HC595 for current drive.

11

Thanks CrossRoads, I will try to get that. Thanks!

12

Sorry, should have been a 2nd link there - ULN2803 as current driver buffer on output of 74HC595.