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???
09/09/07 23:38
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 		 #144186 - LM79XX need a different treatment!
Responding to: ???'s previous message
Jan said:
It was even worse with 79xx-s, I've "burned" quite a couple of them until I learned to be paranoid with decoupling and minimum load.

LM79XX regulators urgently need at least 1µF tantal or 25µF aluminium electrolytic at output for stability. Otherwise they oscillate in the 100kHz region.

Violating minimum load requirements can make the input voltage appear at output! And: Minimum load increases with increasing input voltage!!!

Kai

List of 125 messages in thread
TopicAuthorDate
89C2051 oscillator does not oscillate (?)            01/01/70 00:00      
   Capacitor value?            01/01/70 00:00      
      20-40pF indeed            01/01/70 00:00      
         it might be the crystal            01/01/70 00:00      
            Probably not            01/01/70 00:00      
               because it\'s crap            01/01/70 00:00      
                  Not same position            01/01/70 00:00      
                     one cap or two makes most probably no difference..            01/01/70 00:00      
                        Not on the pins            01/01/70 00:00      
                           I'd recomend you re-read the spec's ...            01/01/70 00:00      
                           It's the same Vcc            01/01/70 00:00      
                  Hhm...I wouldn't recommend this paralleling            01/01/70 00:00      
                     hummm... really? In what frequency range?            01/01/70 00:00      
                        The inductance of the left resonating with...            01/01/70 00:00      
                           interesting            01/01/70 00:00      
                        Spice models            01/01/70 00:00      
                           Thanks, Kai.            01/01/70 00:00      
                           Numerical calculation, some examples...            01/01/70 00:00      
   Wrong reset scheme!            01/01/70 00:00      
      10µF reset capacitor to Vcc            01/01/70 00:00      
      Isn't that the mfg's recommended circuit?            01/01/70 00:00      
         Which do you mean?            01/01/70 00:00      
            10 uF to Vcc and 8.2K (built-in?) to GND            01/01/70 00:00      
               no, it is not            01/01/70 00:00      
                  If it's in nearly every datasheet ...            01/01/70 00:00      
                     this is your perception of the things, Richard            01/01/70 00:00      
                        Here we go again ...            01/01/70 00:00      
                           ... and again...            01/01/70 00:00      
                              I don't know what to say ...            01/01/70 00:00      
                                 there is NO out of spec power supply            01/01/70 00:00      
                                    Not only...            01/01/70 00:00      
                                       Not allways            01/01/70 00:00      
                                       Have you seen evidence of improvement?            01/01/70 00:00      
                                          Wider spectrum            01/01/70 00:00      
                                             maybe ratio of good/bad crystals is the same...            01/01/70 00:00      
                                                In all the various designs I produced ...            01/01/70 00:00      
                                                   Never had a failure until now            01/01/70 00:00      
                                                   I know of lots of crystal problems...            01/01/70 00:00      
                                                      Could be, but I've never encountered it ...            01/01/70 00:00      
                                                      %$#@! Double-post again ... ...            01/01/70 00:00      
                                       ^%$#@! double-post ...            01/01/70 00:00      
                                    If the datasheet says 1 ms ...            01/01/70 00:00      
                           more about locomotives            01/01/70 00:00      
                              symptoms suggest ...            01/01/70 00:00      
                     steam locomotives            01/01/70 00:00      
                        I like the steam locomotives            01/01/70 00:00      
                           So do I            01/01/70 00:00      
                              me too, said the dog            01/01/70 00:00      
                                 The kids should be smarter than that!            01/01/70 00:00      
                                    kids are kids            01/01/70 00:00      
   It might not be a clock problem            01/01/70 00:00      
      Does not work, sorry            01/01/70 00:00      
   Bad Connections or Crystal ?            01/01/70 00:00      
      A picture may be useful            01/01/70 00:00      
         Breadboards are highly unsuited for micros!!            01/01/70 00:00      
            Makes sense            01/01/70 00:00      
            breadboards are highly unsuited for ANYTHING!            01/01/70 00:00      
               Not at all!            01/01/70 00:00      
                  If you look at the pictures you can see why.            01/01/70 00:00      
                     Yes, it doesn\'t look properly, but...            01/01/70 00:00      
                        It's too risky!            01/01/70 00:00      
                           What is the purpose of your posts??            01/01/70 00:00      
                              My purpose is to point out that there are flaws            01/01/70 00:00      
         *** THE PICTURES ***            01/01/70 00:00      
            Problem may be breadboard            01/01/70 00:00      
               Breadboard correction            01/01/70 00:00      
                  How I programmed the 2051            01/01/70 00:00      
               Must be continuous            01/01/70 00:00      
               there is a good english word \'IS\"            01/01/70 00:00      
            I have the same thing running on my desk...            01/01/70 00:00      
               really ?            01/01/70 00:00      
                  Sadly, it's a trade name            01/01/70 00:00      
                  yea, but...            01/01/70 00:00      
                     again, replacing one uncertainty with another            01/01/70 00:00      
            I see two points            01/01/70 00:00      
   When you\'re ready to give up ... try this!            01/01/70 00:00      
      wow            01/01/70 00:00      
      use the unbuffered parts            01/01/70 00:00      
         It works fine with S, LS, HC, AC, HCT, ACT, etc            01/01/70 00:00      
            It's not so foolproof            01/01/70 00:00      
               I've had pretty good results ...            01/01/70 00:00      
   Many thanks, I'll try some of your tips...            01/01/70 00:00      
      Maybe your AT89C2051 is just damaged?            01/01/70 00:00      
      Overtone            01/01/70 00:00      
      89S51/52 are much more stable            01/01/70 00:00      
   Can you still (re-) program it            01/01/70 00:00      
      Let's hope that Rubem will come back ...            01/01/70 00:00      
         Hi again, sorry            01/01/70 00:00      
            Even with no breadboard            01/01/70 00:00      
               What has the programmer to do with the oscillator?            01/01/70 00:00      
      The chip is fine            01/01/70 00:00      
         What will that tell you about the oscillator?            01/01/70 00:00      
            It is time to tell the manufacturer, that...            01/01/70 00:00      
               oscillator of 2051?            01/01/70 00:00      
                  Sorry, maybe I was too harsh            01/01/70 00:00      
                     The MCU and crystals are all working for sure            01/01/70 00:00      
                        It was not the 7805            01/01/70 00:00      
                           because you shook/dropped/kicked it            01/01/70 00:00      
                        7805 decoupling            01/01/70 00:00      
                           LM79XX need a different treatment!            01/01/70 00:00      
                        Good news            01/01/70 00:00      
                           Is this >good news< ??            01/01/70 00:00      
                           Have you considered the "breadboard" effect?            01/01/70 00:00      
                              Inductance            01/01/70 00:00      
                                 Hey!            01/01/70 00:00      
                                    So what?            01/01/70 00:00      
                                       specifically            01/01/70 00:00      
                                       Let\'s not go overboard ...            01/01/70 00:00      
                                          This does not make him learn to swim...            01/01/70 00:00      
                                             I have only my own experience ...            01/01/70 00:00      
                                          Not Atmel problem            01/01/70 00:00      
                                          things change            01/01/70 00:00      
                                             looking at the wrong characteristic            01/01/70 00:00      
                                                OT: to Richard            01/01/70 00:00      
                                                   OT: I hadn\'t but I have ... Yes, I\'m interested!            01/01/70 00:00      
                                       You are probably right            01/01/70 00:00      
                        do you have a 10-100nF directly across the            01/01/70 00:00      
                           *** PCB and schematic ***            01/01/70 00:00      
                              I cannot find C1            01/01/70 00:00      
                                 Ahh, it is the supercap! Needs some changes!            01/01/70 00:00      
                                    Surprisingly It works like it is            01/01/70 00:00      
                                       No, no...            01/01/70 00:00      
                              I can't really 'read' your PCB but ...            01/01/70 00:00      
                                 It is connected            01/01/70 00:00      
   Is any old recipe.            01/01/70 00:00      

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