Hi everyone,
I'm venturing into my first "real" design outside of my lab at school. I thought I'd just do a simple mood lamp using 3 3.5W RGB leds. I just wanted someone to check my schematic and make sure the math/design looks suitable. I'm using a atmega168 to drive the darlington array which will provide the power to the leds. The idea here was to PWM each red, blue, and green from the same PWM pin since there are only 6 PWM pins on the chip. Therefore, I chose the resistor coming from the PWM to be 4.7kΩ, which will provide about 1mA, but current divides 3 ways into the base of each arrary. β for the array is about 1000, so that would put me at about 350mA for each led. Leds are common anode, so I chose 4Ω and 10Ω 1Watt resistors to drop part of 5V to get the desired drop across the led. I'm debating on using a single transistor for the last array since I won't really need to use the rest of the inputs there, but I haven't made up my mind since I have a bunch of them just laying around. Any comments?
I'm venturing into my first "real" design outside of my lab at school. I thought I'd just do a simple mood lamp using 3 3.5W RGB leds. I just wanted someone to check my schematic and make sure the math/design looks suitable. I'm using a atmega168 to drive the darlington array which will provide the power to the leds. The idea here was to PWM each red, blue, and green from the same PWM pin since there are only 6 PWM pins on the chip. Therefore, I chose the resistor coming from the PWM to be 4.7kΩ, which will provide about 1mA, but current divides 3 ways into the base of each arrary. β for the array is about 1000, so that would put me at about 350mA for each led. Leds are common anode, so I chose 4Ω and 10Ω 1Watt resistors to drop part of 5V to get the desired drop across the led. I'm debating on using a single transistor for the last array since I won't really need to use the rest of the inputs there, but I haven't made up my mind since I have a bunch of them just laying around. Any comments?