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Can you stack/parallel an LM1117-3.3

Discussion in 'General Electronics Discussion' started by Kenneth Tan, May 24, 2015.

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  1. Kenneth Tan

    Kenneth Tan

    58
    6
    May 22, 2015
    I've got a load of LM1117-3.3 voltage regulators.
    They are of the SOT-223 type, and have a maximum output of 800mA.

    In the event I would need 1A output current could it be possible to place two LM 1117 in parallel?

    There is a battery backup example schematic in the manufacturer pdf. It only has a blocking diode for the battery. Do I need these diodes if no battery backup is used?

    And in case it's possible, do I need to double the capacity of the caps?
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,284
    2,583
    Nov 17, 2011
    This is not a good idea. You'd have to add a mechanism for sharing the current load among the regulators - a comon problem with paralleling any power supply.Unfortunately there is no explanation in the datasheet how this battery vbackup scheme is supposed to work reliably.

    Here's an application for an external power transistor to boost the output current of an LDO. I think that's the beter way to go. As current increases, it is agood idea to increase the capacity of the buffer capacitors on the input side to keep input ripple voltage low.
    On the output side you need to carefully study the datasheet. Many regulators become instabel when presented wit a loo high capacitive load as this directly influences the regulation loop.
     
  3. hevans1944

    hevans1944 Hop - AC8NS

    4,594
    2,149
    Jun 21, 2012
    The TI Application Report is for a different LDO regulator, and it says their circuit is not recommended for output voltages less than nine volts because of inadequate transient response and stability problems, whatever that means. Your Mileage May Differ. However, I am sure there are similar circuits available somewhere on the Internet that will work with the LM1117 after a little bit of experimentation... I just haven't been able to find any.
     
  4. cjdelphi

    cjdelphi

    1,096
    104
    Oct 26, 2011
    Either place low ohm resistors on the outputs or just use a pass transistor for current loading (npn power transistor)
     
    davenn likes this.
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