Increasing power output of TLC5940

Other Hardware LEDs and Multiplexing
1

I am in need of driving around 180 mA worth of LED's from each channel of a TLC 5940, but the limit on each channel is 120mA. The basic setup is 8 super brite RGB LED's in parallel, fed from a 12VDC power sullply. Can I use a 2N2222 transistor to increase the power output of the 5940 and still maintain the capability to "dim" the LED's with the PWM control? I would appreciate any advice. Thanks

2

Yes but two things:-

  1. You loose the constant current function so you have to have resistors to limit the current.
  2. You invert the signal so the numbers work the other way round, plus you will not be able to totally turn off the LEDs. This is because on a TLC5940 there is always a clock period when everything is off, when you invert this it turns to one where everything is on, you don't see the former but you do the latter.
3

Can the TLC5940's be wired to have parellel outputs for greater current sinking/shared current sinking thru an LED? Maybe with a current limit resistor on each to draw no more than their specified limit?

4

It sounds like connecting two TLC5940's in parallel maybe the best choice. Can you explain more about wiring in resistors to limit the current going to the TLC's so that they share the load evenly.

5

No need to use a resistor they will share themselves, make sure the shared outputs are in the same chip.
However if you are going to run the LEDs in parallel as well, why not just split up the LEDs into a channel each on the TLC5940.

Are these common anode or cathode RGB LEDs? You can only drive common anode ones on the TLC5940.

6

The LED's are common anode. I debated about splitting them up, but I thought it would lead to the possibility of more programming issues. The lights are mounted in a plexiglass housing, so to keep the effect I want the colors have to be solid. In other words if I split them up I don't ever want to have to deal with half going red and the other half blue and vice versa.

7

In other words if I split them up I don't ever want to have to deal with half going red and the other half blue and vice versa.

So you are willing to compromise the hardware design for a tiny insignificant software convenience?

The thing is you can't put LEDs in parallel without using resistors.

8

Thanks for the help. To elaborate a little more, the project is for a mad scientist scene in a hauned house. Basically I am using these LED candles to control colors of beakers that change as the scene plays out. When I first started out doing the haunted house I was all about building controllers to control a specific effect. But as I have quickly learned it is far better to build generic controllers that can work universally on all of my effects. So when something happens to a controller in the middle of the event, all I have to do is grab a spare one, dump the repective program onto it, and swap it out. Less than 5 minutes and I am back up and running. In order to do this I have standardized all my connections. Which means the hardware side is more demanding initially but come show time, it is worth its weight in gold. For the LED's they are all driven by 12vdc, so regardless of how I control them with the TLC's they have to have resistors so that if i swap out the large controllers if one goes down it will still work, or even if I switch out the controller altogether and just go to straight power due to the time crunch. Any rate thanks so much for the help.