I have been working on a LED project for a few years now. Over time the project has evolved mostly due to the increased use of LED's in general, and thus the improved technology available.
My project is for a LED string. It started as a fix to an existing LED string that failed. When I took this existing string apart, I found the reason for the failure. It was using only bias resistors to maintain current across the LED's. It appears that when one LED in the string failed, excess current caused damage both to other LED's as well as the circuit board that the LED's were mounted to. (visible in the attached picture).
Currently I have a circuit and a functioning prototype that uses a LM334 (constant current source) a transistor, and a resistor to run up to 5 LED's per string. The full string consists of 20 LED (4 Strings) interleaved so that if a single string were to fail, the LED strip wouldn't have a blank spot but instead would just have some light drop out.
The current circuit is able to maintain regulation from about 8v up to 16v.
Right now, intensity is controlled by adjusting the current through the lamps.
I'd like to make improvements, so the question I'm posing here is should I just leave it alone, or are there some simple improvements I could make? Package size is a limitation, though I've already determined the LED's will go in the small package (singe line of led's) and the controls can sit outside the container the LED's go in.
Some ideas I've thought of. Implement PWM to handle brightness and possibly decrease LED heating to increase their life.
Switch to some sort of microcontroler.
Switch to some sort of IC (recently interested in the MAX16807 http://www.maxim-ic.com/datasheet/index.mvp/id/5257) but not sure how to implement.
the problem is, since I haven't really finished this... I keep trying to mess with it and improve things. Do you think I've got it good enough?
My project is for a LED string. It started as a fix to an existing LED string that failed. When I took this existing string apart, I found the reason for the failure. It was using only bias resistors to maintain current across the LED's. It appears that when one LED in the string failed, excess current caused damage both to other LED's as well as the circuit board that the LED's were mounted to. (visible in the attached picture).
Currently I have a circuit and a functioning prototype that uses a LM334 (constant current source) a transistor, and a resistor to run up to 5 LED's per string. The full string consists of 20 LED (4 Strings) interleaved so that if a single string were to fail, the LED strip wouldn't have a blank spot but instead would just have some light drop out.
The current circuit is able to maintain regulation from about 8v up to 16v.
Right now, intensity is controlled by adjusting the current through the lamps.
I'd like to make improvements, so the question I'm posing here is should I just leave it alone, or are there some simple improvements I could make? Package size is a limitation, though I've already determined the LED's will go in the small package (singe line of led's) and the controls can sit outside the container the LED's go in.
Some ideas I've thought of. Implement PWM to handle brightness and possibly decrease LED heating to increase their life.
Switch to some sort of microcontroler.
Switch to some sort of IC (recently interested in the MAX16807 http://www.maxim-ic.com/datasheet/index.mvp/id/5257) but not sure how to implement.
the problem is, since I haven't really finished this... I keep trying to mess with it and improve things. Do you think I've got it good enough?
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