I need to make a quick circuit to blink/toggle a 'high powered' RGB led.. (meaning not an accent led of 20mA or so).. it will NOT remain on for a long period of time.. (but I'm sure I'll heatsink the star itself)
actually this is the RGB in question,...the notoriously 'backwards' labeled DealExtreme 3W RGB star:
Its a common anode RGB.. (read comments)
dealing with large current like this is a bit out of my comfort zone.. so I figured Id post and talk it through here first.
I plan to wire it up like this, (well not that many RGB's,...just the one):
keeping the board/components somewhat simple..and easy for me to handle/understand..
the circuit/board will have:
voltage regulator, decoupling caps..
some PNP resistors..
some pads for the battery pack to be soldered to..
some pads for the Arduino signal wires to be soldered to..
Open questions/concerns: (or things I need to be walked through better)
1.) the steady +3.3v powering the RGB.... The Green & Blue should be fine.. with out any resistor on it..(although I was taught always use a resistor).. however the red will need one.. as its fV is 2.5v-3.0v,... if the link is to be believed....
as this large of a current.. I'd need like a 1watt resistor or something?? (kinda bulky..and defeating the SMD purpose of this little board/circuit then)
another/better way for this?
2.) the 1K resistors on the Arduino lines.. not sure how to bets figure out the correct values for here (I know its some magic equation of some sorts?) HAHA..
these are used to be able to saturate the transistor enough to get the FULL POWAH!! through it yes?...
I was thinking.. could I calculate these values to NOT be able to saturate the transistor fully and hence 'resistor' it that way enough for the red?
the pins I use most likely will be digital on/off pins..(not PWM pins)
any other improvements..or things I should make note of?
I am not sure what +3.3v regulator I should use that is SMD still in nature.. but has more than the the typical 150-200mA current limit.. needs to be able to at least give 350mA at a time to any 1 channel of the RGB star/led..
then of course a PNP type transistor choice??.... (usually only have used NPN for common cathode led arrays...etc..and again those were fairly small current needs of only 60-140mA)...
I know there is a bit of a voltage drop across one...but what spec/rating do you look at on a datasheet to know if it can OUTPUT enough current through it?..
for NPN type, SMD sized transistors.. I have used these:
- Vebo / Emitter-Base Voltage = +5v (this is the MAX INPUT voltage from the Arduino pin.. +5v is fine..as its a +5v based logic board)
- Ic / Collector Current (DC) = 800mA (this is the MAX OUPUT current the transistor can pass/putout....correct?)
- Ices / Collector Cut-off Current = 100nA (anything UNDER this rating given to the collector and the collector will NOT open/will close)
- Iebo / Emitter Cut-off Current = 100nA (anything under this comign form the GND of the battery source and it will not work/open)
now for the PNP type I need for this project...???
do I need to be checking the Ic/Collector Current ratings to ensue I can pass enough current through it to power the RGB star/led?
any other specs to be aware of that might effect this?
here is my current schematic to start with and to go along with the thread:
I think I'll stop there before I confuse myself more by over thinking things! LOL