?Brand new and high quality.
?High brightness, light and color consistency.
?Color: Red, Green, Blue.
?Viewing Angle: 140 degree.
?Wavelength: R:620-630nm G:515-525nm B:460-470nm.
?Voltage(Vf): R:2.0-2.5V G:3.2-3.6V B:3.2-3.86.
?Luminous intensity: R:30-35lm G:40-45lm B:15-20lm.
?Current: each 350mA.
No problem, I solder some 20 gauge wire to the leads, tape it to a old Intel Pentium III heatsink, pick some bigger value resistors (three, on the cathodes) and work out the pins.. It's one common to +5V (common anode, right?) and one lead to +0V (cathode?) for each of the three LEDs in the package. Since I am running it at 5V I figure 5000mV/350mA (14.28) to drive it at I should try 15 ohm resistors and see it shine. It does. However, 5V * .35A =1.75 watts per LED = 5.25 watts per package. So, the questions.
They say .35A each above which I run it at, yet this would seem to be 5.25 watts which exceeds the spec of 3 watts. The package did not burn out or anything, but I didn't run it that long because...
I only have 1 watt rated resistors and boy do they get warm quick being run at 1.75 watts each. It seems a waste of energy. Is there a better way?
So should I use multiwatt resistors, drop back to, say, 30 ohms which puts me under the contradicting specs and also fixes the resistor issue, or what? It's a nice LED. Driven at 5V with 3 15 ohm resistors it really is a little star.
Please check my math, I don't know what I am doing.
It does. However, 5V * .35A =1.75 watts per LED = 5.25 watts per package. So, the questions.
They say .35A each above which I run it at, yet this would seem to be 5.25 watts which exceeds the spec of 3 watts.
The 5V is divided between the resistor and LED... Some of that wattage is being used (wasted) to heat-up the resistors.
P.S.
So basically, you can't assume the current is 350mA... And since the voltage drop across each LED color is different, the current through each color is also different (when the resistors are the same). Because of the way LEDs work, you can assume that the rated voltage is dropped across the LED, and the difference between that LED-voltage and your power supply is dropped across the resistor. From the calculated voltage across the resistor, you can use Ohm's Law to calculate the current through the resistor (which is the same current flowing through the LED in series).
And FYI - High power LEDs are normally powered from a constant-current switching supply, which is more efficient than using a resistor as a current limiter.
Sure Electronics sells one they claim is PWM-able... I don't know for Sure. I would stay away from them, they won't stand behind ANY warranty... I was Stoopid enough to try it twice and failed both times, to get a $30.00 piece of stuff from them repaired ( they told me to ship it back... both times. Funny thing was they didn't supply an address to ship it to or any mention of an RMA... Both times.
Power management is important for LED lighting, especially ss somewhat more powerful LEDs are available(!) Recommendations For You - DealeXtreme. Constant-current switch-mode power supplies are the usual approach for LED lighting but that complicates PWM dimming (but should allow analog dimming).
MarkT:
Power management is important for LED lighting, especially ss somewhat more powerful LEDs are available(!) http://dx.com/p/prime-100w-8000lm-led-emitter-metal-plate-pure-white-42806. Constant-current switch-mode power supplies are the usual approach for LED lighting but that complicates PWM dimming (but should allow analog dimming).
No actually the Switching rate is so fast it can be thought of as analog, many PWM current limiters have PWM control inputs that just gate the signal off and on.
it to a old Intel Pentium III heatsink, pick some bigger value resistors (three, on the cathodes) and work out the pins.. It's one common to +5V (common anode, right?) and one lead to +0V (cathode?) for each of the three LEDs in the package. Since I am running it at 5V I figure 5000mV/350mA (14.28) to drive it at I should try 15 ohm resistors and see it shine. It does. However, 5V * .35A =1.75 watts per LED = 5.25 watts per package. So, the questions.
