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Per Westermark
02/29/12 08:33
Read: 170 times
Sweden


 		 #186277 - More common long time ago
Responding to: Erik Malund's previous message
Erik Malund said:
just, generally, a horrible design.
It seems, that the 'designer' (if you can call him that) just threw something together heving no concern for LED survival, no concern for intensity variations, I could go on ....

Erik

This design wasn't too uncommon 20 years ago, with older diodes having a completely different behaviour. Old LEDs could handle huge current spikes without a problem, and could run with extreme multiplexing as long as the average current wasn't too high. And there wasn't pesky laws about power factor correction of loads, except for industrial-sized installations. And a cheap transformer can scale down the voltage to human-safe voltages. And slightly reduce the overtones on mains.

An interesting thing with a long LED chain is that if one LED gets a short, the voltage over the LED chain will decrease and the voltage/current over series resistor will increase. Besides extra heat in this resistor, another marginal LED could fail. I have seen some nice LED chains where every LED have shorted. I'm not sure if it's just some LED types that fails to short or if they normally go to open, but with 12 shorted LEDs in same chain I kwow that at least some LED may fail with a short.

List of 27 messages in thread
TopicAuthorDate
AC Powered LEDs + strobe      Chico Magalhães      02/28/12 22:58      
   Isolated Switch      Jim Granville      02/28/12 23:39      
      Switching      Chico Magalhães      03/15/12 00:41      
   Some basics      Oliver Sedlacek      02/29/12 00:54      
      Not a good design - and expensive        Per Westermark      02/29/12 03:00      
         Answers + need some explantion      Chico Magalhães      02/29/12 23:55      
      Cap voltage      Chico Magalhães      03/01/12 00:03      
         More than 280V      Oliver Sedlacek      03/02/12 04:30      
            Measurement      Chico Magalhães      03/15/12 00:45      
               Measurement correct      Erik Malund      03/15/12 07:54      
   two caps polarity reversed on DC!! ?      Erik Malund      02/29/12 07:13      
      More common long time ago      Per Westermark      02/29/12 08:33      
         I was around then      Erik Malund      02/29/12 09:21      
            Some polarized capacitors survives AC but not reversed DC      Per Westermark      02/29/12 10:01      
               POOOOOOOOOF      Erik Malund      02/29/12 10:27      
                  Yes, very likely a failure      Per Westermark      02/29/12 11:10      
                     that need bold face      Erik Malund      02/29/12 11:44      
            Back to back connection...      Kai Klaas      03/02/12 17:05      
   And another thing...      Andy Neil      02/29/12 15:30      
      Pseudo-CC with resistor requires much % V over resistor      Per Westermark      02/29/12 16:52      
      chip      Chico Magalhães      03/01/12 00:11      
         one of these      Erik Malund      03/01/12 08:00      
         Chips      Andy Neil      03/01/12 14:33      
   PC PSU      Chico Magalhães      03/15/12 00:47      
      Definitely better with lower voltage design      Per Westermark      03/15/12 01:11      
         PSU      Chico Magalhães      03/15/12 18:37      
            Some bricks can inform about rating      Per Westermark      03/16/12 02:21      

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