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???
03/23/07 16:44
Modified:
  03/23/07 16:46
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 		 #135681 - Exactly! But not only a tad...
Responding to: ???'s previous message
Erik said:
mains power need be (a tad) higher than the battery voltage

The nominal voltage across the storage cap behind the regulator should be way higher. Otherwise, the battery is discharged over and over again during mains undervoltage situations, which can occur unexpectedly often!

Eugene, we have discussed similar applications in the past here. Maybe you can "pump" some information from the following threads?

http://www.8052.com/forum/read.phtml?id=71623
http://www.8052.com/forum/read.phtml?id=104203

By the way, what current would your application draw from the battery?

Kai

List of 32 messages in thread
TopicAuthorDate
Diverting power supply to battery            01/01/70 00:00      
   Battery?            01/01/70 00:00      
      Picture of 9V battery            01/01/70 00:00      
         Diode OR            01/01/70 00:00      
            a note to the above            01/01/70 00:00      
               AC Adaptor = 12V, Battery = 9V            01/01/70 00:00      
                  5V regulator            01/01/70 00:00      
                     Regulator used            01/01/70 00:00      
               Exactly! But not only a tad...            01/01/70 00:00      
            Can\'t seem to find the 3-pins package            01/01/70 00:00      
               It's an SOT-23 and very common ... see DigiKey            01/01/70 00:00      
                  Still having trouble looking            01/01/70 00:00      
                     how much current?            01/01/70 00:00      
                        Current not measured....yet            01/01/70 00:00      
                           You need to know that!            01/01/70 00:00      
                              Alright, will measure and get back to you asap!            01/01/70 00:00      
                                 Requirement?            01/01/70 00:00      
                                    The situation            01/01/70 00:00      
                                       Alarm            01/01/70 00:00      
                                          Alarm is actually a high output buzzer            01/01/70 00:00      
                                             Buzzer            01/01/70 00:00      
                                                Agree            01/01/70 00:00      
                                       Battery backup for alarm systems            01/01/70 00:00      
                                          Just to make everything simpler...            01/01/70 00:00      
                                             Security system...            01/01/70 00:00      
                                                Student Assignment            01/01/70 00:00      
                                                   a happy 'professor'            01/01/70 00:00      
                           fast switching double diode            01/01/70 00:00      
                           You can calculate current requirements            01/01/70 00:00      
                     description is important            01/01/70 00:00      
   Oh, how often            01/01/70 00:00      
      University project            01/01/70 00:00      

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