[sdiy] 7-segment LED displays with 4511 driver chip - max current?
rick.jansen at xs4all.nl
Wed Aug 5 18:32:10 CEST 2015
I need three 7-segment digits for a small project, and am looking at the common 4511
driver to drive them. There are numerous examples around of circuits to do just that, but
I'm a bit puzzled. The specs for the 4511 say that it can source 25 mA max current, per
pin. However, with a max total of 50 mA for the entire package. So, if you light ALL
segments, excluding the dot, that would be 50/7 = 7 mA max current per segment.
Only TI says 7.5 mA explicitly : http://www.ti.com/lit/ds/symlink/cd74hc4511.pdf
A very common value in available circuits for the current limiting R is 470Ω, which gives
ca 10 mA, but which would exceed the total current for the package. Even 220Ω is common,
which indeed delivers 20 mA to one LED segment, but may fry the 4511 if you light 7
segments with 140 mA.
How do you use the 4511?
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