Regulated Power Supply Help

Discussion in 'The Projects Forum' started by Dan., Sep 16, 2007.

  1. Dan.

    Thread Starter New Member

    Sep 16, 2007
    Hi Guys,

    Sorry to join the forum and jump straight in with a question but....

    Basically I need to make a regulated power supply for in car use (typically 11-16 volts, the reason for th large voltage swing is a VERY LARGE stereo system i.e 16KW RMS, voltage normally sits between 12 & 14 volts but can vary depending on levels of charge in the battery bank & load on the system)

    The power supply is to power one NAS drive which requires a 4amp supply @12V DC and one audio player (a squeezebox) which requires a 1amp supply @5V DC.

    The power supply has to be well regulated and have as smooth output as possible, could anyone point me to a circuit diagram, kit or product which would fit the bill? A ciruit diagram or kit would be preferable as i like making things but failing that a prebuilt module would suffice.

    Any help would be appreciated & I will post up a build thread if I do end up making one :)
  2. SgtWookie


    Jul 17, 2007
    For the 5V, 1A supply, take a look at the LM117/LM317; datasheet is available from National Semiconductor's website.

    (The major differences between these IC's are the temp ranges, packages and cost)

    I suggest the LM117/317 over the LM78xx series, because it's adjustable from 1.2v to 37v, is a more modern design, and has many more features than the LM78xx series does - and they're very inexpensive. There are a number of application examples in the datasheet, which will be most helpful and directly applicable.

    While you're there, take a look at the LM138/LM338 regulator. It'll handle up to 5 amps, but they are QUITE a bit more expensive than the LM117/LM317. However, the LM138/LM338 is a nifty single-chip solution to your 12V 4A supply.


    Don't forget you'll need filter caps on both the input and output for your application, as your regulator will be a ways from both the battery and your equipment.

    Look on page 9, at Figure 3 "Regulator with Protection Diodes" - adding a large input cap along with a small bypass cap would complete your 5V 1A supply.

    There are many more applications beginning at page 15. Have a look at page 21 in particular.

    Don't forget to provide adequate heat sinking. It won't necessarily kill these IC's, but they'll shut down if they get too warm.

    Oh, and don't use the "switching" supply examples for this project - you will be very unhappy with the added noise.
  3. Dan.

    Thread Starter New Member

    Sep 16, 2007
    Many thanks I have downloaded the datasheets and will take a look over this week whilst im away with work :)
  4. Art

    AAC Fanatic!

    Sep 10, 2007
    Thanks, informative for me too :)