1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

LDO replacement for 7805?

Discussion in 'Datasheets, Manuals or Parts' started by Krumlink, Sep 5, 2007.

  1. Hero999

    Hero999 Banned

    Joined:
    Apr 6, 2006
    Messages:
    14,902
    Likes:
    79
    Location:
    England
    Use a voltage regulator with the current rating you require or boost it.

    Have you actually tried parralleling them?

    I agree that it isn't a good idea in general but I wouldn't totally rule it out. It might not be as Nigel suggests, as one will start to shut down and reduce its voltage slightly, the other might start to take the strain more. I suggest you try it, use a suitable heat sink for the power dissipation and try measuring the input current to each regulator. I might experiment with this myself as I'm interested to see exactly what will happen.
     
  2. Krumlink

    Krumlink New Member

    Joined:
    Aug 10, 2007
    Messages:
    2,080
    Likes:
    20
    Location:
    Michigan, USA
    I'll Add a heatsink to the D2 and put a fan on it to help throw away the heat. I will try paralleling them and stuff. My Binary clock is almost done, I just gotta hook up the displays.
     
  3. mvs sarma

    mvs sarma Well-Known Member

    Joined:
    Oct 29, 2006
    Messages:
    3,512
    Likes:
    76
    Location:
    Hyderabad, India.
    I have recently come across a SAMSUNG component KA78R05 it is a low drop device and it has a 4th pin to shut down in case of overcurrent. the Datasheet is attached.
     
    Last edited: Jul 7, 2008
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,440
    Likes:
    933
    Location:
    Canada, of course!
    ONLINE

    Samsung? It looks like it is made by Fairchild.
     
  6. mvs sarma

    mvs sarma Well-Known Member

    Joined:
    Oct 29, 2006
    Messages:
    3,512
    Likes:
    76
    Location:
    Hyderabad, India.
    You are right Sir, it is by Fairchild.
     
  7. 3v0

    3v0 Coop Build Coordinator Forum Supporter

    Joined:
    Jul 14, 2006
    Messages:
    9,404
    Likes:
    227
    Location:
    OKLAHOMA USA
    Some regulator datasheets show a schematic where they use a transistor in conjunction with the regulator to provide more current then the regulator itself can supply. Could this be used with a LDO regulator?
     

    Attached Files:

  8. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,440
    Likes:
    933
    Location:
    Canada, of course!
    ONLINE
    Yes it can but it needs to have an additional 2nd transistor to provide current limiting.
     
  9. Hero999

    Hero999 Banned

    Joined:
    Apr 6, 2006
    Messages:
    14,902
    Likes:
    79
    Location:
    England
    Also not that you have to add Vb + Vce at the desired current to the dropout voltage.
     
  10. eng1

    eng1 New Member

    Joined:
    Apr 7, 2006
    Messages:
    951
    Likes:
    19
    Location:
    Italy
    I would add only |Vbe| to the drop-out voltage of the regulator, ΔVreg.
    And |Vce| = |Vbe| +
    ΔVreg when the transistor is on.


    EDIT: as far as I know, there are LDO regulators that can source 750 mA or more, as the OP requires.
     
    Last edited: Sep 10, 2007
  11. mvs sarma

    mvs sarma Well-Known Member

    Joined:
    Oct 29, 2006
    Messages:
    3,512
    Likes:
    76
    Location:
    Hyderabad, India.
    Perhaps there are low current devices as well while the one KA78R05 for e.g., can give 1amp load.
     
  12. eng1

    eng1 New Member

    Joined:
    Apr 7, 2006
    Messages:
    951
    Likes:
    19
    Location:
    Italy
    Yes, I've read the datasheet you posted.

    For my requiremets I usually use the LM2937 (500 mA max). For more current, I have few LM2940's (Io = 1 A max, the drop-out voltage is 0.5 V typ. and 1 V max).
     
  13. mvs sarma

    mvs sarma Well-Known Member

    Joined:
    Oct 29, 2006
    Messages:
    3,512
    Likes:
    76
    Location:
    Hyderabad, India.
    Well - you are right we don't get so free a supply of these LDOs in small Qty / retail. Incidentally one auctioner provided us with this chip(78R05) and finding comfortable.
    when a component is not on hand in 3D, only a 2D document (pdf) is to be enjoyed. Perhaps Digikey will supply and i shall be spending few$+$50 for the international post iteself.
    For eample, here i needed CY27EE16ZE to complete an Elektor (5/07) Project (Software Defined Radio) . Hope to get it some day!!
     
  14. mneary

    mneary New Member

    Joined:
    Feb 27, 2007
    Messages:
    4,502
    Likes:
    67
    Location:
    California USA
    If it turns out that you need two regulators to handle the total load, you don't need to hook their outputs in parallel, just use one to supply the LEDs and the other to supply the TTL.
     

Share This Page