Multiple LED drivers with a common positive?

[Matt Thorn]

I wanted to post this in the LED String Blade forum, but for some reason I can't post anything on that forum.

I'm making my first LED string blade, and I'm thinking about using six 7027 BuckToot 350mA constant-current LED drivers for each of the six sections of the blade. I'm putting it in a converted Force FX Vader, and planning to maintain the scrolling effect. (I'll be using the standard battery/speaker pack that comes with the Vader Force FX.)

So my question is this: Is it possible to have positive leads forking out from the VDD on the board to the "VIN +" lines of the BuckToots, and the have "LED +" leads on the other side come together again in the common positive lead of the LED string...? I've made a diagram illustrating what I want to do. Hope it's decipherable.

[Equality 7-2521]

According to this sim, it will.

[Matt Thorn]

According to this sim, it will.

Wow! Thank you! I once downloaded a circuit-simulation program, but I couldn't make heads or tails of it. I will give it a "real world" test tomorrow and let you know how it works. The next question is if I can coax 2100mA out of the Force FX board. Wish me luck.

[Equality 7-2521]

Here's the schematic import for anyone who wants to download (import) and run the simulation.

---START---
$ 1 5.0E-6 0.019691167520419408 10 5.0 50
v 272 448 272 384 0 0 40.0 3.0 0.0 0.0 0.5
162 464 144 400 144 1 2.0 1.0 0.0 0.0
162 464 112 400 112 1 2.0 1.0 0.0 0.0
s 208 448 272 448 0 1 false
s 304 448 368 448 0 1 false
162 464 208 400 208 1 2.0 1.0 0.0 0.0
162 464 240 400 240 1 2.0 1.0 0.0 0.0
v 368 448 368 384 0 0 40.0 3.0 0.0 0.0 0.5
s 400 448 464 448 0 1 false
162 464 304 400 304 1 2.0 1.0 0.0 0.0
162 464 336 400 336 1 2.0 1.0 0.0 0.0
v 464 448 464 384 0 0 40.0 3.0 0.0 0.0 0.5
w 272 384 368 384 0
w 368 384 464 384 0
w 400 336 400 448 0
w 464 384 512 384 0
w 512 384 512 336 0
w 512 336 464 336 0
162 464 80 400 80 1 2.0 1.0 0.0 0.0
162 464 176 400 176 1 2.0 1.0 0.0 0.0
162 464 272 400 272 1 2.0 1.0 0.0 0.0
w 400 80 208 80 0
w 208 80 208 448 0
w 464 336 464 304 0
w 464 304 464 272 0
w 464 272 464 240 0
w 464 240 464 208 0
w 464 208 464 176 0
w 464 176 464 144 0
w 464 144 464 112 0
w 464 112 464 80 0
w 400 80 400 112 0
w 400 112 400 144 0
w 400 272 400 304 0
w 400 304 400 336 0
w 400 176 400 208 0
w 400 208 400 240 0
w 400 176 304 176 0
w 304 176 304 448 0
---END---

[Matt Thorn]

Um... Okay. I have no idea what any of that is, but if it means I can have a common positive on both sides of six LED drivers, that's a good thing.

[Equality 7-2521]

Sorry, that wasn't very clear.

The simulator applet that I linked to can be downloaded and run locally, plus it also allows importing/exporting of schematics. The text above is the import data to recreate your schematic.

[Sunrider]

Ambitious you are. I like it.
For more current upgrade pcb transistors?

[Matt Thorn]

Sorry, that wasn't very clear.

The simulator applet that I linked to can be downloaded and run locally, plus it also allows importing/exporting of schematics. The text above is the import data to recreate your schematic.

Haha. No, you were clear enough. It's just that the data looks like alphabet soup to me. And with my current limited understanding of electronics, I doubt I could use the applet anyway. But thanks all the same.

[Matt Thorn]

Ambitious you are. I like it.
For more current upgrade pcb transistors?

I did think about adding transistors, but it hadn't occurred to me to replace those on the Force FX board with higher gain transistors. Brilliant thinking. That might eliminate the need for the BuckToots entirely. Either way, I'm a bit worried about whether or not the 3-AA battery pack will be sufficient.

[Matt Thorn]

I'm still unable to post anything on the LED String Blade forum.

The Buck Toot drivers produced nothing. Nada. Nary a flicker.

So I tried a "standard" direct connection like the one Eastern introduced here.

I'm using 66 30mA LEDs, with 11 LEDs per section. The first four sections are fine, but I'm having trouble getting the sections 5 and 6 to light up. I assumed it was a loose connection, and though I do get those sections to flicker faintly when I jiggle the wires, the connections seem solid.

Will the last two sections not light up because the first four are sucking up all the current?