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Help needed in building a white LED cicuitry

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losT

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Hi,
I need some help in building the above circuit. The major problem is I couldn't find a white LED which is at least 40 cd and 60°C in angle. Therefore I need to use array of LEDs. How do I connect the array of LEDs with a switch which can control the light intensity?? I will be good if someone could show me the schematic. Pls help.
 

Klaus

New Member
I very much doubt that you'll find *any* LED with a 40cd rating.
40mcd yes. I have just bought a white LED with an 8000mcd rating and 20 deg. viewing angle, there may be more powerful ones around but it will be a while before we see 40,000mcd (40cd) LED's.
You can control the light intensity by changing the current through the LED or, if you have an array, you can change the current to all LED'd. This would be preferable to switching individual LED's as then you no longer get the light spread of an array. BTW, fit a diffuser as well for a more even spread of the point source light.
Each LED should have its own dropping resistor. To control the light output vary the supply voltage after you calculated the resitor value at the max voltage.
Example (substitute specs of your own LED's):
I LED = 25mA
V supply = 12V (max)
Vf LED = 3.6V
VR = V - Vf = 12 - 3.6 = 8.4V
R = VR/ I = 8.4/.025 = 336 (use 330 Ohm resistors for each LED)

Klaus
 

tansis

New Member
The best schematic for a LED flashlight that I've seen so far was published by
www.elektor-electronics.co.uk
in the november 2002 edition.Sadly I am not allowed to upload the article due to copyright restrictions. You could try asking them for a copy though.

What I can say though,

Some of best LEDS you can buy are made by a company called Nichia (japan) ref NSPW 500BS [6400mCd!]

Maxim make a couple of ic's for driving leds or you can use the ever popular 555. If on the other hand you want a really neat flashlight then a PIC 12C672 might come in handy.......

http://dbserv.maxim-ic.com/appnotes.cfm/appnote_number/1804/ln/en
http://dbserv.maxim-ic.com/appnotes.cfm/appnote_number/1750/ln/en

You may also want to take a look at battery chargers for Lithium-ion cells as they are very suitable for this application.

Build your own solar cells
http://www.solideas.com/solrcell/english.html

Led flash-light pages
http://www.e-f-w.com/community/index.php
http://www.e-f-w.com/community/modules.php?name=News&file=article&sid=10
http://www.sentman.com/led/durabeam.php
http://www.solorb.com/elect/solarcirc/solarfl/

http://dbserv.maxim-ic.com/appnotes.cfm/appnote_number/913/ln/en
http://dbserv.maxim-ic.com/appnotes.cfm/appnote_number/897/ln/en
 
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