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Tracffic sign with LED

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amindzo

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Hi, i want to make a traffic sign LED and i want to turn on 19 LED. every LED consume 20-25mA and i need to design a power source that give every LED just 20mA. could yoy help me with this? how should i connect the LED's? parallel or series&parallel?
 

Re: Traffic sign with LED

Usually clusters of LEDs are driven in series strings of 6 or less but sometimes many more. In your case you might have 2 strings of 6 and 1 of 7 or 1 string of 4 and 3 of 5. If you're making the clusters, you can wire to stay within your voltage budget. If you're buying prewired clusters, then you must supply whatever voltage their design requires. I especially like the Supertex CL series of linear constant current drivers for projects like this (bottom of page) **broken link removed**. What supply voltage are you using?
 
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5 volt, because i have a microcontroller in this circiut. i want to turn on and off the LED's ( Flashing mode). The IC's you introduced have this possibility or we need extra circiut or microcontroller for this application?
 
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You can run from 5V, but then you would need a separate driver or dropping resistor for each LED (3 X 19 = 57). I recommend that you use a separate 24VDC power supply for the LEDs. 24 volts is the highest commonly available DC supply voltage that is still low enough to be intrinsically safe. Most of the Supertex IC's I suggested are capable of external control from your microcontroller. What are your LED specifications and are you able to use surface mount components?
 

i want to make something like this and i want to know that what kind of LED do you suggest?
 

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Re: Traffic sign with LED

Any high brightness LEDs. The trick is in getting the viewing angles and brightness matched and the colors correct. Viewing angles are easy since they're in the LED specifications. To match brightness, you should compare lumens (you may have to convert from millicandelas and viewing angle). You can get a good idea about correct colors in nanometers by looking at specifications for commercial LED traffic signals. Are you able to use surface mount components? Do you have at least 6.5 VDC available?
 
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i have done this and it works well for 44 LED, but there is a problem. if one LED is going out of order we have 4 LED off (one row is turning off) what can i do to solve this problem? (if one LED is out of order only one off LED)
 

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actually you have connected led's in series that's why your all 4 led's gone if one will open. if u'll connect led in series then there will be no solution, u can design your structure in zig-zag manner or connect each led independently or say parallely.
 
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