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9vdc off 12vdc using LM1084 to Drive Web Cam — Parallax Forums

9vdc off 12vdc using LM1084 to Drive Web Cam

Bill ChennaultBill Chennault Posts: 1,198
edited 2009-03-30 15:59 in General Discussion
All--

I can almost understand some of the words on a datasheet now! However, for me it is best to ask folks that know, still.

Can I use the circuit shown in the LM1084 datasheet (marked 1.2V - 15 Adjustable Regulator, using an LM1084-Adj to get 9vdc from my 12 volt lead-acid batteries? All I need is 200ma.

Is there a better way?

Thanks!

--Bill

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You are what you write.

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-03-30 00:32
    Looks good to me. Make sure to use an adequate heatsink. You'll be dissipating 0.2A x 3V = 0.6W. That's not a lot, but still enough to need some kind of heatsinking.

    Do read the section of the datasheet on output stability. Depending on what you plan on powering, you may need more than the minimum output capacitance.

    Post Edited (Mike Green) : 3/30/2009 12:38:04 AM GMT
  • Bill ChennaultBill Chennault Posts: 1,198
    edited 2009-03-30 00:53
    Mike--

    Great!

    I've got some 10uF and 22uF solid tantalum caps coming my way. I'll use the 22uF caps.

    So far, all my regulators are TO-220 form factor. I bought a bunch of TO-220 form factor heat sinks, as well.

    Thank you!

    --Bill

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    You are what you write.
  • UghaUgha Posts: 543
    edited 2009-03-30 11:36
    If you want extremely good heat dissipation you should consider using thermal paste between the regulator and the heat sink. This will help the transfer quite a bit.

    At this low of a wattage it's not such a huge deal, but it might be a good practice to start.

    Just be careful! All the best pastes (Arctic Silver 5) are conductive... so make sure you don't get it on the pins, just the metal tab on the back.
  • RobotWorkshopRobotWorkshop Posts: 2,307
    edited 2009-03-30 13:28
    Bill Chennault said...
    I've got some 10uF and 22uF solid tantalum caps coming my way. I'll use the 22uF caps.

    Hello Bill,

    What is voltage rating on the tantalum caps? When choosing caps you'll want to make sure that your working voltage (what will normally be applied across the cap) is well under what the cap is rated for. It is my understanding that this is even more important in regards to Tantalum capacitors. If you do some searches on "tantalum capacitor derating" there are some pretty good articles online about it. Some say that you should only use a voltage about 30% of what is marked on them. I think the newer Tantalum caps are much better than the older stuff but you may want to keep that in mind when using them.

    Robert
  • Bill ChennaultBill Chennault Posts: 1,198
    edited 2009-03-30 15:59
    Ugha and Robert--

    Ugha, I use thermal paste between all my heatsinks and regulators. I cannot claim to have known to do it. Someone told me. Someone on this forum.

    Robert, I ordered 25 volt tantalum caps. I am going to subject them to 12 volts. So, I guess I will find out sooner or later if they should have been 40 volt caps. Gee. I hope it is later. If not, Digi-Key is really going to like me.

    --Bill

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    You are what you write.
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