[dorkbotpdx-blabber] ARRGGHH - Please check this circuit

[Hans Lindauer]

I'm using a computer PSU, it's rated at 30A @5V, 315W max.  It's ~7W for 
R+G+B (total, not per color), plus 5W per UV LED, so for 10xRGB + 6xUV 
LEDs, the total power should peak out at about 10*7+6*5=100W+losses. 


Eric Garner wrote:
> my first question is "what's supplying the power to all this?" is your
> supply hefty enough to supply (10W* 36 LED's+ Losses=380-400W?)
>
>
>
> On Mon, Jan 12, 2009 at 5:53 PM, Hans Lindauer <armatronix at sbcglobal.net> wrote:
>   
>> 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)
>> R1=100Kohm, 1/4W
>> R3=0.56ohm, 3W
>> 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
>> (I'm not using the amber die on the LED)
>> Link to Instuctables page for this circuit
>>
>>
>>
>> Thanks!
>> -Hans
>>
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>>     
>
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