12v and 5v power supply

Discussion in 'General Electronics Chat' started by Dritech, May 23, 2012.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi all,

    I want to build a power supply where the 5v will be used to power the PIC, LCD and some other ICs and the 12V will be used to power a 12V 2A motor.

    If i use the attached power supply circuit, will it work fine?? are the 0.33uF and the 0.1uF capacitors enough?

    By the way, the first regulator is the LM1084IT-ADJ and the second regulator is the 7805.

    Thanks in advance.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Whats the Vin voltage going to be?
     
  3. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi, the input voltage will be supplied from a laptop power supply (19V 4.7A).
     
  4. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,871
    1,394
    If you want only 12v and 5v, there is no need to use an adjustable regulator in the first stage. The 1084 is also a low dropout regulator, which is not really needed in your application. In addition, a heat sink will be required if you pull 2A from the 1084.

    The 7805 circuit is straight from the datasheet, but an additional 10μF eletrolytic on the output wouldn't hurt. Again, depending on the current you pull, a heat sink may be required. By using the output from the first stage as the input to the 7805, you do reduce the heat from the 7805. The laptop power supply should be fairly well filtered.
     
  5. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi, the reason for using the 1084 is since it can handle 5A and i bought an adjustable one since the fixed ones are not available locally. So you suggest that i don't use this regulator??

    BTW the motor will only be on for few seconds.

    Thanks in advance.
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It should work; it just has more capabilities than necessary.
     
  7. paulktreg

    Distinguished Member

    Jun 2, 2008
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    I know half of the fun is in the building but have you considered using a PC ATX power supply?
     
  8. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Yes but it is too bulky for my project.

    Thanks for your replies.
     
  9. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi again,

    Is it safe to connect both the LM1084 and the 7805 to the same heatsink or will i short them??
    And is it ok if i use an 11-5-1cm aluminum block (without slots) as a heatsink??
     
  10. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Any help please?
     
  11. BSomer

    Member

    Dec 28, 2011
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    106
    You can use the same heatsink if you insulate them from each other. The tab on the 7805 is connected to ground and the tab on the 1084 is Vout. So if the two tabs are touching the same heatsink a dead short has been made. It would be best to eliminate any chances of that happening by using separate sinks.


    This is fine. The aluminum will draw away the heat from the devices. Fins just create more surface area to dissipate heat.
     
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