I did the same with an atmega88 recently.I've used a constant current driver with mosfet found at the instructables-site. It took me 4 components/colour worth $3 in total.Basics of the driver are described here :http://www.instructables.com/id/Power-LED-s---simplest-light-with-constant-current/In step 6-8 of the next instructable (same author) is shown how you can use an pwm-pin to drive it.http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/
BTW, My dog strongly disagrees the "Lightning" menu of my mood light is part of an "Hello World" application ]
I've found this tutorial too, but I haven't found such FETs locally, what is a subsitution?What power supply have you used? How efficient (how hot were drivers?
Quote from: Simpson_Jr on Jan 26, 2011, 08:57 pmBTW, My dog strongly disagrees the "Lightning" menu of my mood light is part of an "Hello World" application ]Sorry, I haven't understand the joke
Main reason for me was that the voltage drop of the green/blue leds was quite high, the voltage drop of normal NPNs I had laying around would also be quite high and I was afraid I never could light 'm full power at 5 volts.
Can I ask what NPN has such big voltage drop? I plan to feed 1W LED from 5V with resistor and PWM it using plain old BC337. Will BC337 introduce voltage drop on its own?
2. If you look up the minimum specified gain (worst case), and the amount of current you want to pass through the transistor, then you can calculate how much base current you need. If you multiply that base current by 2 or 3 or 5 then you will be sure to be driving the transistor into saturation.
3. I can not imagine that there is any silicon transistor that is not capable of at least 500KHz. But that is a number that you can look up in the spec sheet.
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