LM3407 and leaded components?

Discussion in 'The Projects Forum' started by JMD, Jan 15, 2010.

  1. JMD

    Thread Starter Member

    Dec 9, 2009
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    While im waiting for parts for my AC-LED project, ive started on the DC-LED project. This involves a tiiiiiny IC:
    [​IMG]
    Data sheet: http://www.national.com/ds/LM/LM3407.pdf (circuit in question here, is the typical application).

    NS suggests the use of SMD components - which differ a tiny bit, compared to leaded components. I havent worked much with SMD components before, so my primary concern, is:

    The inductor.. It must be 33uH and have a DCR between 100u and 3.3 ohm. Found one that should have a DCR of 0.045 @ 33uH - should be just fine? Im unsure whether i want a high or low value here..



    Anything i should be aware of, when using leaded components instead of the suggested SMD's ?
     
    Last edited: Jan 15, 2010
  2. SgtWookie

    Expert

    Jul 17, 2007
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    DCR = DC resistance value. Lower = better, but the inductor will be larger in physical size due to the larger wire used, thus higher in cost. The higher the DCR, the more power loss you'll have in the inductor.

    Get the lowest DCR that you can for the price in a size that will fit on your board.
     
  3. JMD

    Thread Starter Member

    Dec 9, 2009
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    Superb! Well, since i live in Denmark, everything is expensive. Those SMD inductors costs $2 each, and minimum order is 5. Leaded costs the same.

    Then i might aswell buy leaded components - and if they are better aswell, then the choice isnt hard.
     
  4. t06afre

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    May 11, 2009
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    Hi JMD try www.elfa.se I live in scandinavia and use them as my component pusher. They take mail orders
     
  5. t06afre

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    I would also say you do not have to use SMD components. But try to put all components as close as possible, or even closer to the IC. Good luck. I can guide you to find the a good inductor if you need it
     
  6. JMD

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    Dec 9, 2009
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    Ill give the URL a try :) I usually use http://www.rs-online.com/index.html - very professionel, but a bit expensive!


    I find one thing weird tho.. NS states that the Cin (between capacitor must me 2.2 uF and 100V. I see no reason at all, that justifies the need for a 100V cap. Same goes for the cap between Gnd and the pin "VCC" (and also goes to "DIM", to keep it at 100% duty cycle).

    Vin is max 30V, so i cant see why a 100V cap would be needed those two places.


    EDIT: Okay, ive tried Elfa now, but.. i dont like the layout of that site. It makes no sense at all. Feel free to link a 33uH inductor. I tried to find one, but that site isnt user friendly. RS on the other hand.. so nice search features!
     
    Last edited by a moderator: Feb 7, 2010
  7. t06afre

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    This is not so difficult. On the left hand menu select
    passive komponenter->drosselspoler->minityrdrosler then you will see several choices for inductor types. I think the Radiel miniaturedrossel, RM 5 mm series should be just what you need
     
  8. JMD

    Thread Starter Member

    Dec 9, 2009
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    I cant seem to find any 42,2k resistor - can you? 1/8W should be enough.
     
  9. t06afre

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    Do search for 42,2kohm ;)
     
  10. JMD

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    Dec 9, 2009
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    I searched for "42,2k" - zero hits. "42,2kohm" - One hit. Not an intellegient seracher, thats for sure ^^

    Still like RS alot more - much easier to find what you need. On Elfa you have to search for whatever you need, because there are so many categories, you would need to go thru. Looking at metal foil resistors, there are these categories:

    - Metalfilmsmodstand, 0,4 W, type MRS16S
    - Serviceemballage, 0,4 W
    - Metalfilmsmodstand, 0,6 W
    - Serviceemballage, 0,6 W
    - Metalfilmsmodstand, 0,6 W, type MRS25
    - Metalfilmsmodstand, 1/2 W
    - Metalfilmsmodstand, 1 W, type PR01
    - Serviceemballage, 1 W
    - Metalfilmsmodstand, 2 W, type PR02
    - Serviceemballage, 2 W
    - Metalfilmsmodstand, 3 W, type PR03
    - Serviceemballage, 3 W


    But.. i just wanted to look for a metal foil resistor :confused:

    Oh well.. gonna compare prices with RS, when they are finished updated their servers :)
     
  11. t06afre

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    Nothing beats a printed catalog ;)
     
  12. JMD

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    Dec 9, 2009
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    Hm.. Regarding the inductor: NS states the lower bound for the inductor, to be at least 0.6A. To meet that requirement, Elfa only got 2 inductors - bots are axial (not counting SMD ones).

    Id rather go with an radial one, but i dont think they got any that meets the requirements.
     
  13. t06afre

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    I think you will be able to part number 58-830-20. Even if is SMD type it is a quite large component (for a SMD) so you will be able to solder like a hole mount component
     
  14. JMD

    Thread Starter Member

    Dec 9, 2009
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    Thats a 22uH :) I need 33uH. The axial one i looked at, was the 58-085-14. DCR @ 0,076 Ohm - sounds good! And its capable of handling 3 times the needed current.
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Sorry that inductors are so expensive in your area.

    You should check out Ron Dekker's great page:
    http://www.dos4ever.com/flyback/flyback.html
    He gave it the title of "Flyback Converters for Dummies" in jest; there is really a great deal of good information on that page.
     
  16. JMD

    Thread Starter Member

    Dec 9, 2009
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    Not sure what you want me to look at there, but i like the Nixie-driver!

    I passed my "Applied Electromagnetics" course, so ive covered the basics of electromagnetism, and quite a bit beyond that :p Only thing we didnt cover, was the DCR.


    At this moment, im waiting for these to arrive:
    [​IMG]

    Should make the IC's a bit more managable. Then i just need to order rest of the parts!


    Semi-offtopic: Anyone know a good place to look for used Tektronix oscilloscopes (digital ones)?
     
  17. JMD

    Thread Starter Member

    Dec 9, 2009
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    Yea, like i guessed.. too big footprint. Cant trust the chinese!


    Any difference between MSOP-8 and eMSOP-8 ?
     
  18. JMD

    Thread Starter Member

    Dec 9, 2009
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    Anyone know?
     
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