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Lukas Valecky
07/01/09 07:35
Modified:
  07/01/09 08:01
Read: 465 times
Jablonec Nad Nisou
Czech Republic


 		 #166617 - Relay control - 8051...
Hello all,

I only would like to know if there could be any problem when a 5V relay is connected to AT89C51ED2 only across one PNP transistor - BC857. Coil power is 200 mW (5 V * 0,04 A). If the pin goes LOW the base current is about 1 mA that is enougth for collector current up to 100 mA...

There is my schematic:
Save This Code

                                |--------|Pull-up resistor 10k|--------|Vcc|
                                |
|Base|--------|Resistor 4k7|----*---|pin of MCU|

|Emitter|--------|Vcc|

|Collector|----*---|Relay|---*----|GND|
               |             |
               |---|1N4148|--|


I only found divergent opinions on the Internet without final conclusion :-( Darlington is often mentioned but I think this schematic works similarly and in additon it is simpler, isnt it? Thank you very much for you help...


List of 18 messages in thread
TopicAuthorDate
Relay control - 8051...      Lukas Valecky      07/01/09 07:35      
   looks good to me but ...      Erik Malund      07/01/09 07:58      
   Concept seems fine...        Michael Karas      07/01/09 09:58      
   re: relay control      Andy Peters      07/01/09 14:57      
      NPN and standard '51?      Jan Waclawek      07/01/09 15:03      
         standard 8051      Andy Peters      07/01/09 16:32      
            Ye standard 8051 and the C8051Fxxx ...      Michael Karas      07/02/09 01:15      
               two times only...      Steve M. Taylor      07/02/09 02:40      
                  Relay Drive: Previously, on 8052.com      Andy Neil      07/02/09 03:02      
            'ED2 is "biblical" as far as ports are concerned      Jan Waclawek      07/02/09 03:04      
   snubber      Lukas Valecky      07/02/09 04:03      
      At both needed!      Kai Klaas      07/02/09 07:04      
         AC opener...      Lukas Valecky      07/02/09 07:22      
            12V AC?      Kai Klaas      07/02/09 07:49      
               yes...      Lukas Valecky      07/02/09 08:22      
                  I would drive it by a DC source!      Kai Klaas      07/02/09 08:32      
                     Just have seen...      Kai Klaas      07/02/09 16:01      
                        a little information      Lukas Valecky      07/03/09 01:36      

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