[dorkbotpdx-blabber] ARRGGHH - Please check this circuit
armatronix at sbcglobal.net
Mon Jan 12 20:53:24 EST 2009
By now, many of you have been blinded by my MIDI LED project at the
meetings. Hopefully some of the electronics experts out there can help
me get this thing working so I can get on with my life.
The trouble is, I've been trying to run the whole thing off of 5V, but
when the lights come on fully, it /appears/ (I don't have a scope to
confirm this) that the voltage drops below the minimum for the
microcontroller, causing the microcontroller to reset.
I had hoped that putting a capacitor on the microcontroller's power rail
would help (I even figured out to put a diode going into the cap), but
it still isn't working. I think the problem is that 5V doesn't provide
enough overhead, and trying to use caps to take up the slack is only
going to be marginal at best if I want to be able to run the LEDs at
full brightness (which I do).
So my next step is to try powering it off of 12V instead of 5V.
/BUT.../ when I tried that before, it burned out my LED after a few
minutes (and I can't afford to burn out too many of those, they're
expensive). The guy who posted the driver circuit I'm using claims that
it works for 3V-60V, but obviously I've found an exception to that.
I don't understand this stuff enough to know what's the problem here,
but if any of you do, could you please let me know what to try next?
And if there's a Better Way (that won't break the bank or introduce a
lot of complexity), I'm open to suggestions.
Here's the driver circuit; I have 36 of these in the system, hooked up
to the Dorkboards' PWM outputs:
I=1A thru the LED (metered at 5V input)
Q1=Fairchild 2N5088BU Small Signal NPN Transistor data sheet
Q2=Fairchild FQP50N06L 60V N-Channel QFET Logic Level MOSFET data sheet
LED=LedEngin LZ4-20MA10 Hi-Power LEDs on MCPCB RGBA 10 Watt Full Color
data sheet <http://www.ledengin.com/products/10wLZ/LZ4-00MA10.pdf>
(I'm not using the amber die on the LED)
Link to Instuctables page for this circuit
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