Want to pay for: 19V Linear Power Supply

Discussion in 'The Projects Forum' started by sevenpoints, Jul 21, 2010.

  1. sevenpoints

    Thread Starter New Member

    Jul 19, 2010
    5
    0
    Hi everyone,

    I'm new to this forum, and don't really have the skills or understanding (my brain freezes when I look at circuit diagrams) necessary to build my own electronics, but I do know what I need in this case.

    I'm looking for someone knowledgeable here who can build me a clean, completely linear power supply with the following specs:

    - AC-DC
    -115-130V AC in, 19V regulated DC out, very small voltage fluctuation (if that's the right term to use)
    -Maximum current of 6.3 A, though able to deliver even 4.7 A would suffice
    -Needs no fan for cooling
    -Preferably in a case

    I hope it's okay to post this here. If not, I apologize.

    I don't have a huge budget, but if there's anyone here who can help - I am interested in buying one from someone for the cost of their service, if the price is okay - please do reply, or send me a PM with your email address.

    Thanks kindly!
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    It would be considerably cheaper to buy a SMPS such as this and put a simple linear regulator in back of it.

    http://www.bgmicro.com/PWR1278.aspx

    A linear regulator will be much easier using this as a base.
     
  3. Markd77

    Senior Member

    Sep 7, 2009
    2,803
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    Or search for bench power supplies. You will probably find them as cheap as building your own.
    <ed> Just checked Bill's link. That's really cheap </ed>
     
  4. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    That's a pretty good price on a supply, Bill..
     
  5. BMorse

    Senior Member

    Sep 26, 2009
    2,675
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    heck yeah that's a good price! The one's I have been using have been costing me over $50.00 (although they are rated at 8 amps, and these are only 6.5, but I am only using 5 at the most...)!! I will have to have purchasing give them a call and maybe get a stockpile of these things..... Thanks Bill...

    B. Morse
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    I think Wookie's local shop has them too, Marlow, MJ electronics? They are out there from several companies. I have several I'm going to turn into variable power supplies (maybe).
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Marlin P. Jones & Associates is who you're trying to think of, Bill.
    http://www.mpja.com

    They'll run a very similar switching supply on sale occasionally at that same price. I've never tried this, but if you call 'em up and point out that BG Micro has that supply on sale for $15, would they care to match it? They just might do it...

    BG Micro has been around for a good while, I've never heard any complaints about them, and I wouldn't hesitate to order something from them. I simply haven't ordered anything from them before.

    Since MPJA is just a few hours from me, I get my orders really fast; usually the next day.

    I've only had one item get broken in shipping from MPJA; that was a single ferrite toroid. I informed them about it in an E-mail, and suggested the packaging personnel be informed that ferrite toroids are rather fragile and need better packaging - but to not send a replacement as the shipping would cost the company far more than the toroid was worth.

    If I need more, I'll place another order. I always order more than I need, as you have to plan on some attrition (loss of parts for various reasons). The one that arrived broken was a planned-for spare.

    The points here are is to always shop for a deal from a reputable seller, order more quantity than you absolutely need because you may very well need some spares (particularly if you are a n00b), and if something arrives broken or otherwise defective, try to take a reasonable approach towards solving the situation.
     
  8. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    Cosel Electronics, eh? Has Howard come back in a third form -- an electronics company owner? He was a lawyer before he worked with Meredith and Gifford.

    You young pups probably haven't a clue who I'm talking about... :p







    ** Yeah, I know, it was spelled Cosell...
     
  9. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    19V....... Sounds awefully much like a laptop PSU
     
  10. sevenpoints

    Thread Starter New Member

    Jul 19, 2010
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    Wow, I leave the thread for a day or two, and BAM - loads of replies. Well, thanks everyone for your answers, some directed at me, some directed at one another ;) ...

    I looked around for bench power supplies, but couldn't find anything within specs of what I'm after. Regarding the first reply by Bill, I hear what you're saying, but I want to try this totally linear (or as linear as can be, so far as the power supply is concerned); so ideally I wouldn't attach a switchmode power supply to a linear regulator. I can just as easily find a fixed voltage switching laptop PSU, but again, I'm after linear.

    I guess there are no takers on building one for me, huh? Any thoughts on how to try n' make it myself? The parts I'd need? The last time I talked to someone from DigiKey, they told me they don't offer design advice, and I cannot for the life of me figure out what's online in the language (of electronic design or engineering) it's written in.

    Or have I missed the most basic of designs?

    Seriously, I am open to people's offers to make one if they're not uberexpensive.

    Cheers
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    One of the big problems with your requirements is that linear regulators regulate voltage by using semiconductors as variable resistors. This implies power dissipation in the regulator. In order to keep the range of output voltage low, you'd have to have a rather large transformer with a low impedance output, and large filter capacitors, just for starters.

    You would also need a large and expensive heat sink to mount the regulators on. Since you don't want it to be fan-cooled, the heat sink would have to be that much larger to compensate.

    It would also not be very efficient - maybe 60% or so.

    For a custom-built linear supply in that range, you'd probably be looking at around $250-300, plus another $50 or so for shipping. It will be large and very heavy. It will also make a good room heater while making your electric meter spin rather quickly.

    Switching regulators do have some ripple on the output. The ripple can practically be eliminated by using output LC filters.

    In contrast, a switching supply would be compact, lightweight, efficient, and relatively low-cost.
     
  12. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
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    The easy way around this is to design a stock standard low current powersupply. You can use an LM7815 and use bias resistors to bring it up to 19V. You then just need to add one or two 2N3055 transistors as current bypass to get the current you require. I have a 13.8V 30A power supply at home and this is the method it uses. The only thing limiting the current is the nuber of transistors (I have 5) and the size of the transformer (mine is huge).
     
  13. k7elp60

    Senior Member

    Nov 4, 2008
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    I have checked with most of the distributors that I purchase from and the transformer just for the power supply is pretty close to $50.00. I may have a couple of transformers in my stock that would do the job. If you can send me a personal message (PM) perhaps I can help you, as I have lots of linear regulators and rectifiers that would do the job.
    Ned
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    You will note, the OP says they don't have any experience. I was trying to simplify his life a lot with the SMPS suggestion, it would take care of a heavy transformer, rectifiers, filters, and most of the heat generated. BTW, a computer power supply could not do this, this is a off the shelf part that would get you into the ball part (handling all the heavy lifting), and you would finish with a linear section to do a clean filter and finish of it without a space heaters worth of heating or a box that will be in the 3' X 3' X 2' range.

    The OP obviously has it figured out though, so good luck!
     
  15. sevenpoints

    Thread Starter New Member

    Jul 19, 2010
    5
    0
    Folks, I'm sorry to have bothered you! I did end up finding a linear bench power supply that looks like it'll meet what I need. Thanks again for all of your responses.

    Cheers
     
  16. campeck

    Active Member

    Sep 5, 2009
    194
    3
    just bought two of those supplies. what a deal!
     
  17. sevenpoints

    Thread Starter New Member

    Jul 19, 2010
    5
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    Hello again everyone,

    though my response above probably still applies (have found a pretty clean sounding linear adjustable bench/lab power supply (with a heatsink), I somehow failed to notice that more people had replied on the second page of this thread.

    My apologies for having missed your responses. I'm going to look over them. Thanks again!
     
  18. sevenpoints

    Thread Starter New Member

    Jul 19, 2010
    5
    0
    Sorry to bump my own thread, but k7elp60, if you're reading this, you know what? The power supply I ended up trying doesn't look like it's going to work out. I may be interested in working with you after all.

    I can't PM you (not enough posts I suppose), so am hoping you see this and send me an email. Would you mind getting in touch with me at the following email address?: seven.points.mail@gmail.com

    Thanks; hope I can reach you.

    Cheers
     
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