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???
06/06/09 01:02
Modified:
  06/06/09 01:03
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 		 #165891 - High power led driver
Hello, I bought recently a 3W RGB Led, 1w per color, 350mA per color.
2,2V to 2,8V red
3,0V to 3,8V green and blue.

I calculated to use 6,29 ohms resistor to red color (powering by 5V), the nearest I have is 4,7 and it is ok when connected directly to the power (without the driver).
Then I moved to a driver like shown in faqs here, it worked ok too.
Then I thought would be much easier to use a ULN2007 or ULN2803 to drive the leds (good and cheap), but even when just one led was connected to the ULN its bright was not the total bright, current was like 200~250mA
I want to understand why this happens when using the ULN with the led.
Someone can explain me?

Thanks a lot.

List of 30 messages in thread
TopicAuthorDate
High power led driver            01/01/70 00:00      
   Have you accounted for Vce(sat) ?            01/01/70 00:00      
   resistors are not a good solution            01/01/70 00:00      
      Have you considered a current mirror?            01/01/70 00:00      
         mirror, mirror on the wall            01/01/70 00:00      
            No question about it ...            01/01/70 00:00      
               But was that the question?            01/01/70 00:00      
                  I focused on the brightness match ...            01/01/70 00:00      
                     Doesn't it show that he's missed an important point?            01/01/70 00:00      
                        He doesn't really have to consider voltage            01/01/70 00:00      
                           for a (short) while            01/01/70 00:00      
   Sorry for the delay            01/01/70 00:00      
      The ULN works perfectly well - as far as it goes.            01/01/70 00:00      
      MOSFET Technical Info            01/01/70 00:00      
      Key term is 'logic level'            01/01/70 00:00      
         commom part            01/01/70 00:00      
            Catalogue?            01/01/70 00:00      
   Mosfet            01/01/70 00:00      
      I believe you'll have a problem ...            01/01/70 00:00      
         IRF530            01/01/70 00:00      
            Dig a little deeper, Chico ...            01/01/70 00:00      
               circuit... will work if I do this way?            01/01/70 00:00      
                  No!            01/01/70 00:00      
                  Look at the specification for IRLD120            01/01/70 00:00      
                     now i get confoosed            01/01/70 00:00      
                        High power            01/01/70 00:00      
                        He has digressed            01/01/70 00:00      
                           I suspect it's because he needs a constant current switch            01/01/70 00:00      
                              And I suspect that we are wildly guessing...            01/01/70 00:00      
                                 a little more specificity, please, Chico            01/01/70 00:00      

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