Hi! This is my first post.
I recently bought some high intensity RGB LEDs from this site. They are rated at 1W per color:
http://www.dealextreme.com/p/3w-led-emitter-on-star-multicolored-rgb-4530
They are common anode (though they are mis-labelled as common catode, someone says it in the comments) so I soldered three resistors (47 ohm to red, 33 ohm to green and 33 ohm to blue, 2W resistors) to the cathodes. Connected 5V to anode, and ground to the three resistors. And voila, it works! They are very bright and nice.
The problem is that the resistors get very hot. After a minute you almost can't touch them. It scares me to use the LEDs continuosly...
The led itself doesn't get very hot, and I was planning to buy some heatsinks here:
http://www.satistronics.com/high-po...le-for-1w-and-3w-power-led-35mm15m_p2151.html
But now, how am i supposed to cool the resistors?
The LED specifications, according to Dealextreme, are:
Red: 2.5V ~ 3.0V, 350mA
Green: 3.2V ~ 3.8V, 350mA
Blue: 3.2V ~ 3.8V, 350mA
I used 47 ohm for red and 33 ohm for green and blue, so it would give less than the 350 mA maximum for each color, so I wouldn't burn the LED.
With the resistors I used, it gives:
Red: (5V - 2.5V) / 47 ohm = 53 mA
Green: (5V - 3.2V) / 33 ohm = 53 mA
Blue: (5V - 3.2V) / 33 ohm = 54 mA
I'm well under the maximum of 350 mA... what am I doing wrong?
So my question is: is there a better way of turning on the LEDs, so nothing gets hot? Or am I using wrong resistors? They're rated at 2W so I thought they wouldn't get hot.
I'm going to drive the LEDs with a ULN2803 (darlington transistors) controlled by an AVR microcontroller (ATMEGA328P in a breadboard) and do PWM to control the color.
So that's all! Thanks in advance
I recently bought some high intensity RGB LEDs from this site. They are rated at 1W per color:
http://www.dealextreme.com/p/3w-led-emitter-on-star-multicolored-rgb-4530
They are common anode (though they are mis-labelled as common catode, someone says it in the comments) so I soldered three resistors (47 ohm to red, 33 ohm to green and 33 ohm to blue, 2W resistors) to the cathodes. Connected 5V to anode, and ground to the three resistors. And voila, it works! They are very bright and nice.
The problem is that the resistors get very hot. After a minute you almost can't touch them. It scares me to use the LEDs continuosly...
The led itself doesn't get very hot, and I was planning to buy some heatsinks here:
http://www.satistronics.com/high-po...le-for-1w-and-3w-power-led-35mm15m_p2151.html
But now, how am i supposed to cool the resistors?
The LED specifications, according to Dealextreme, are:
Red: 2.5V ~ 3.0V, 350mA
Green: 3.2V ~ 3.8V, 350mA
Blue: 3.2V ~ 3.8V, 350mA
I used 47 ohm for red and 33 ohm for green and blue, so it would give less than the 350 mA maximum for each color, so I wouldn't burn the LED.
With the resistors I used, it gives:
Red: (5V - 2.5V) / 47 ohm = 53 mA
Green: (5V - 3.2V) / 33 ohm = 53 mA
Blue: (5V - 3.2V) / 33 ohm = 54 mA
I'm well under the maximum of 350 mA... what am I doing wrong?
So my question is: is there a better way of turning on the LEDs, so nothing gets hot? Or am I using wrong resistors? They're rated at 2W so I thought they wouldn't get hot.
I'm going to drive the LEDs with a ULN2803 (darlington transistors) controlled by an AVR microcontroller (ATMEGA328P in a breadboard) and do PWM to control the color.
So that's all! Thanks in advance