The 1A 5V supply is five watts, so you can burn 3W forrappa wrote:My first question is how to power the circuit. Would a 5V power supply be a good choice? Something like this ... I want to be able to control each color independently with PWM.
Correct.rappa wrote:I already have a 9V power supply but it seems that would just waste more power?
A bipolar transistor array (like the ULN2003)rappa wrote:As for interfacing with the Arduino, it seems that the Darlington Array is a popular choice. Am I on the right track? I am looking at the ULN2003 and its data sheet says it can handle only 500mA, so would I need 3 of them, one for each color? Also, I am unsure of what resistor values would be appropriate between the Arduino and Darlington.
There are two issues, firstly, you mustrappa wrote:Lastly, the LED manufacturer recommends a heat sink for running at max current. What type of heat sink would be a good choice and how would I bond the LED to it? The LED mounted on a nickel-sized aluminum board.
Yes, use the FETs (they are overkill, unless if you have them already).rappa wrote:I have a few IRF520 N-Channel MOSFET transistors. Would those suffice? I also have a TIP102 and a TIP120 (Darlington).
Be careful not to let the LED cluster overheat. It will die.rappa wrote:As for the heat sink, I'm going to try and scavenge one from my collection of old computers/electronics.
Sure! Do you work with SMD/SMT? There arerappa wrote: If the IRF520 is overkill, could you recommend a better match?
rappa wrote:Here's [a heatsink] I found that might work [...]
The problem I see with this one is that it would need to be upside down and therefore would not transfer heat as well.
unsped wrote:this may sound dumb, but do you have a diagram handy of an io pin hooked to the mosfet with the safety resistor?
rappa wrote:I tried hooking up my LED to the IRF520 MOSFET but it didn't work so well. I uploaded an Arduino sketch that turned the output on and off with a 1 second delay but it never turned off; instead it dimmed a bit but that's it. So any ideas why it wouldn't turn off?
winston wrote:Why not use a purpose built LED power supply IC? Most of them have an input specifically for controlling brightness via PWM, and won't waste a shed load of power like a resistor will (after all, half the point of using an LED is for better efficiency). LED power supplies often can take a wide voltage range.
Purpose built LED power supplies (they are a current regulator - set the current required for your LED) usually just need decoupling caps, an inductor, current sense resistor and a schottky diode as external components.
rappa wrote: Here's what I get:
Gate grounded: LED is offt
Gate at 5V: LED is on
Voltage across drain/source: 33mV
Voltage across LED: ~3.4V
Do the Arduino and power supply grounds need to be common?
rappa wrote: I see that some MOSFETs are listed as Logic Level Gate, but I'm not sure if the IR520 is. Would that make a difference?
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