Peggy 2 – Driving 90mA per LED

[ShaneA]

Hello all,

Now first, I read through Windell’s great discussion already regarding this (here: http://www2.evilmadscientist.com/forum/viewtopic.php?showtopic=2979). But I’m still just a tiny bit unclear on somethings and I like to be sure before I start soldering.

I have 625 LED’s that can handle 90mA no problem, even if some bug in the code keeps them on constantly. 

Now, what resistors should I change on what pins and to what resistance for giving the ability to run my LEDs?

Then besides that I just need a 2.5A power supply (and cooling fans -or fins?- on the LED drivers) and I’m in business, right?

Thank you for the help!

[ShaneA]

I just checked the driver chips, they are different then what I was supposed to get. 

I was supposed to receive STP16DP05 drivers but instead I received STP16CP05 instead.

Normally I wouldn’t care but the DP (what I was supposed to get) is between 5-100mA where as the CP is only 5-80mA.

I really need these to be at least 85mA per LED…

[ShaneA]

I looked further into the datasheet and I see that somehow the CP still allows up to 90mA (from what I see). So If I want 85mA it says I need a 229ohm resistor on the chip. So since there is two per side does that mean I need replace all 4 resistors (2 1k and 2 trimpots) with 114ohm or just short the trimpot and run one 229ohm per side?

Also, it would have to be a 114ohm that holds over 2.5w?? Or how much wattage?

Thank you!

[Windell Oskay]

First off, as you know, setting a limit higher than 30 mA is not “officially supported,” but we’ll do our best to help you out. :)

For maximum current, solder together the two connected (or all three) pins of VR1 and VR2.  Then, put the selected resistors (one per driver chip) into RA1 and RA2.  We are not *aware* of anything else in the circuit that will prevent you from going all the way to 90 mA (besides the temperature of the LED driver chips in free air), but you are in somewhat uncharted territory.

[ShaneA]

So just (2) 229ohm resistors are needed and I’m good (in theory)? Fantastic!

On to my next questions, I’ll start a separate topic soon.

Thank you!

[Author]

Posts