Email: Password: Remember Me | Create Account (Free)

Back to Subject List

Old thread has been locked -- no new posts accepted in this thread
???
07/21/09 05:54
Read: times


 		 #167642 - I suspect it's because he needs a constant current switch
Responding to: ???'s previous message
and he needs it on the high side, so he can still use a low-side driver like the ULN-whatevers that he likes.

He has diverged from the initial proposition. His situation then was that he had three different colors of LED's that he wanted to drive such that he'd have equal brightness, but the three different color LED's had different forward voltages. He subsequently became entangled with the 5-volt supply together with the 2.5-3.2 (or thereabouts) forward voltages of the diodes in combination with his intially chosen USL2803 darlington, which also has a substantial collector-emitter voltage.

Someone, it might have been me, suggested a higher LED supply, and things went from there ... One option that hasn't yet been mentioned is a separate supply for each LED color... Oh, well ... we'll get to that.

RE


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      

Back to Subject List