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???
09/01/06 14:32
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 		 #123504 - see the datasheet, it shows how to do that...
Responding to: ???'s previous message
The original NSC datasheet shows the LM7805 used as an adjustable regulator. That works just fine. It's not the REAL problem, though.

Jan is faced with a different problem. His problem is NOT that the regulator is not performing at the ideal voltage, BUT that is a contributing factor.

He is using a regulator that's specified for 4.75 to 5.25 volt output, provided the input is adequate. His real problem is that some component in his system doesn't function properly, despite the fact his supply is within that range.

He has found that the circuit appears to function properly if the supply is held at or very near 5.0 volts, but it fails if it falls to 4.8 volts.

Clearly, the problem centers around the issue of device specifications. Either one or more components isn't intended to work at that voltage level, or it fails to meet its own specified operating limits.

In neither case is the regulator at fault.

RE




List of 44 messages in thread
TopicAuthorDate
78x05 output voltage tolerance            01/01/70 00:00      
   5%            01/01/70 00:00      
   Selection needed...            01/01/70 00:00      
      5%, 10%, it's all there            01/01/70 00:00      
         for decades, 5% was "standard." What's changed?            01/01/70 00:00      
         What standard do you mean??            01/01/70 00:00      
            "if"            01/01/70 00:00      
               Don't you test your circuits?            01/01/70 00:00      
                  it's already a pain...            01/01/70 00:00      
                     if you do, I'll take my cap off to you :)            01/01/70 00:00      
                  Consider the specifications            01/01/70 00:00      
   is it a Microchip supervisor?            01/01/70 00:00      
      the conclusion            01/01/70 00:00      
         No such thing as luck in any acceptable design sce            01/01/70 00:00      
            everyday we learn something...            01/01/70 00:00      
         Check it with a >5.0V outputting 7805!            01/01/70 00:00      
            it will work...            01/01/70 00:00      
               oh 'testing'            01/01/70 00:00      
            Getting more than 5 v from 7805            01/01/70 00:00      
               I would use a resistor instead of a diode            01/01/70 00:00      
                  see the datasheet, it shows how to do that...            01/01/70 00:00      
                     It's noise, I guess...            01/01/70 00:00      
                        some noise            01/01/70 00:00      
               the u (micro) is only specified to 5.25 or 5.5 Vol            01/01/70 00:00      
   I just had an idea...            01/01/70 00:00      
      Don't go off chasing that rabbit!            01/01/70 00:00      
         digital design practice            01/01/70 00:00      
            Safe side...            01/01/70 00:00      
         Exactly            01/01/70 00:00      
      Getting low output...            01/01/70 00:00      
   get this in your head            01/01/70 00:00      
      Not so fast...            01/01/70 00:00      
         oh, how many designs have failed because            01/01/70 00:00      
            No, no, I have not said this            01/01/70 00:00      
            it depends on the source ...            01/01/70 00:00      
               Yes,...            01/01/70 00:00      
                  There's a critical difference ...            01/01/70 00:00      
                     Of course, there is!!            01/01/70 00:00      
                        whst do you refer to?            01/01/70 00:00      
                           This was in the '70's, before many restrictions            01/01/70 00:00      
                              caught by "legal relabeling".            01/01/70 00:00      
                                 That's not what I remember            01/01/70 00:00      
                                    continuing the story            01/01/70 00:00      
                                       The way it used to work ...            01/01/70 00:00      

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