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Constant current driver question

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krich

New Member
I am putting together a scoreboard project and have made some good progress this week. I now have a prototype diy 7 segment display module built and controlled by a TLC5916IN constant current LED driver. I'm really liking this chip. It has 8 channels, all driven with a constant current and controlled with an SPI shift register. Here's the datasheet:

https://www.electro-tech-online.com/custompdfs/2009/09/tlc5916.pdf

The current can be controlled by the resistor they call Rext. I've been able to use the calculations in the datasheet to calculate the proper maximum current drive for my led strings and it all works great!

Now, here's my question and it's a question probably more out of inexperience and/or ignorance than anything.

I want to be able to dim the scoreboard (for night viewing) with just a single pot or switch, perhaps mounted through the enclosure on the side/back. I will have 4 identical 7 segment displays for the tens and ones digits of both home and away scores, each being controlled by their own TLC5916. Is it possible to use one resistor/pot to control the brightness of all four displays?

Once I figure this out, then the next question is can I use the same strategy to dim all of the TLC5916 driven displays on the scoreboard (there are currently 7 planned)?

Thanks for your input!
 

Diver300

Well-Known Member
Most Helpful Member
You have two choices.

1) vary the current taken by circuit attached to R-ext pin

2) Change the gain setting.

The R-ext pin stays at 1.26 V, so you could just connect the same value resistor to each of the R-ext pins, with the other ends joined together to a common point. The voltage on the common point will vary the current of all of the displays, with the maximum when the voltage is zero and zero when the voltage is at 1.26 V

The gain setting is set through the serial link, by going into special mode and sending the gain. Page 19 of the data sheet says how that is done. That method doesn't need any additional hardware.
 

krich

New Member
Thanks Diver300 for such a clear and concise description of my options. I honestly hadn't had a close look at the configuration options (they were a bit confusing to me at first scan), so I am happy to see that with some studying I can implement as a software configuration.

Cheers! :)
 
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