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???
07/21/10 10:39
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 		 #177402 - Power from USB
Responding to: ???'s previous message
Michael Karas said:
I see you have said that you are obtaining the 5V power from a USB port. Be aware that your USB device will be overloading the USB ports legal current limit. USB ports are supposed to be designed to limit themselves to 500mA at 5VDC.


And the 500mA is only supposed to be taken after proper USB protocol enumeration - you can't just stick a dumb load on the power lines, and pull 500mA

This was discussed at length recently: http://www.8052.com/forumchat/read/176473



List of 42 messages in thread
TopicAuthorDate
common DCtoDC converter suggestion            01/01/70 00:00      
   5 things            01/01/70 00:00      
   Figure 17            01/01/70 00:00      
   Problems2Problems            01/01/70 00:00      
   Pin 6 needs to be connected            01/01/70 00:00      
   I would take the LM2574...            01/01/70 00:00      
      great suggestion            01/01/70 00:00      
         Calculation            01/01/70 00:00      
            new schema            01/01/70 00:00      
               New Schema but Still No Go            01/01/70 00:00      
                  New Schema            01/01/70 00:00      
                     from datasheet and AP+calculator            01/01/70 00:00      
                     Still a No Go            01/01/70 00:00      
                        Change            01/01/70 00:00      
                           In the context of this reguator part...            01/01/70 00:00      
                              Power from USB            01/01/70 00:00      
                              General context of switcher chips?            01/01/70 00:00      
                              Hold on            01/01/70 00:00      
                                 USB 500mA            01/01/70 00:00      
                                    never having sucked power from the USB plug            01/01/70 00:00      
                                       RE: delay from plug-in before you can get 500mA?            01/01/70 00:00      
                                          What's Legal...            01/01/70 00:00      
                           Always too short initial posts            01/01/70 00:00      
                              You may have 500mA (2.5W)            01/01/70 00:00      
                                 Yup..            01/01/70 00:00      
                                    12 more than 33 VDC            01/01/70 00:00      
                                       Don't use 7812            01/01/70 00:00      
                                          Used 2 pieces IC            01/01/70 00:00      
                                             Always problem with available power            01/01/70 00:00      
                                                with automatic fuse            01/01/70 00:00      
               Application Note            01/01/70 00:00      
               MC34063A Calculator            01/01/70 00:00      
                  OK            01/01/70 00:00      
            Help calculating divider resistors            01/01/70 00:00      
               E-series            01/01/70 00:00      
         I misunderstood you...            01/01/70 00:00      
            Refer application note AN920/D            01/01/70 00:00      
               App Note Caution            01/01/70 00:00      
                  Yes, but sometimes...            01/01/70 00:00      
                  I suppose so,            01/01/70 00:00      
                     ????            01/01/70 00:00      
            price            01/01/70 00:00      

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