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Thread: Why can't you build a power supply??

  1. #1
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    Question Why can't you build a power supply??

    Why could you not build a power supply for the ITX boards using LM or equivilent regulators (Regulator that has a Input range of 7-19volt). From what I've read, the ITX board does not require the +12V, and if you have no components in your system that uses the 12V line why not just buy pass it? All my components are USB devices, the hard drive lives of the 5V line. So could you not use LM style Voltage regulators to feed the ATX plug on the mother board???

    (I used the LM as an example, I know it need 12Volt )

    LM1084IT-3.3-ND ( Output 3.3V@5A )

    LM1084IT-5.0-ND ( Output 5.0V@5A )

    The PW-70A outputs:

    +3.3@5A
    +5.0@5A
    -5.0@.2A
    +12@5A
    -12@.2A
    +5Vsb@2A

    With the PW spec, why could you not build a PS for the 3.3, 5 lines and integrate it with the timing components of the ITPS. This would eliminate clutter, since all needed would be 4 regulators plus the timing chip, and it should survive crank?

    Would this be possible??? or is my fever just getting to me.

  2. #2
    FLAC
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    VW,
    From what I've read, the ITX board does not require the +12V
    I keep asking if someone has verfied this. Is it true for ALL motherboards, or does it vary with diff manuf? IF it is true, then YES, your strategy would work.

    Is someone willing to do a little legwork to verify the need for a regulated +12v supply on EPIA and other mobos?? This would be a very nice revelation that would get rid of the need for the expensive Opus.....

    However, I would recommend a simple switching regulator over the (very enefficient) linear regulators. Especially if you start asking for 5+A.
    MikeH

  3. #3
    Raw Wave Rob Withey's Avatar
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    Quote Originally Posted by MikeH
    Is someone willing to do a little legwork to verify the need for a regulated +12v supply on EPIA and other mobos??
    I can't speak for the Epia, but an EM-586 SBC won't boot without the +12V line. It draws very little current on the 12V line though. I'm using a laptop hard drive and the onboard sound and video.


    Rob
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  4. #4
    Maximum Bitrate none's Avatar
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    How is this easier than building a Sproggy?

  5. #5
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    Of Mini-Box's web site: regarding thier PW-70A

    +5V - General M/B and disk circuitry, Memory, laptop drive motors. All Boards All our DC-DC converters have adequate power on this rail

    +3.3V - CPU core, Memory EPIA-5000, 800, V, M/1000, CL, etc All our DC-DC converters have adequate power on this rail.

    -5V - Obsolete NONE No longer needed on any boards.

    +5SB - Memory, vital sleep functions. ALL Uses little power.

    +12V - 3.5", 5.25 motors, fans, P4 power mostly P4 boards (lots of power), FET drive on all boards (little power). Use PW-60a or PW-70a only when using 3.5" drives or P4s.

    -12V - Some older serial ports EPIA-M, EPIA-M2 (EPIA-5000/800/V does not use the -12V for serial ports) Check the serial driver chipset. Modern serial chipsets do not use the -12V rail.


    As to "How is this easier than building a Sproggy?", I don't know.... what I wanted was to find out was if the M-9000 would work with out the +12Volt line, since this is the voltage that seems to give the most truble. As to easier, you could get this power supply down to 5 or 6 components and for $15-$20

  6. #6
    phc
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    One problem I see is heat from using linear regulators - if you are dropping 12V to 3.3V at 3.38 amps, your LM1084IT-3.3-ND would need to dissipate 35.5 watts.

    The 5V reg would be 2.52 amps, dissipating 22.2 watts.

    Thats 57W of heat that needs to be removed from the system for just the mobo, forget about the USB devices that also need 5V. Also, your TO-220 devices cannot really handle that much power dissipation, they heat up 2.7 deg C per watt, so your 3.3V will be at 95 'C above ambient - really pushing it.

    This is assuming a 13.8V or so input - what my car typically runs at. Current is just for the EPIA -M10000 from the power simulator at www.mini-itx.com.

    This is why nobody really uses linear regulators to drop that much voltage, they tend to use higher efficiency switching regulators.

  7. #7
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    You know, I've asked the same question my self for several years. And I found several designs and ideas:

    http://www.epanorama.net/links/psu_computer.html
    (free schematics)

    www.opussolutions.com
    (commercial grade prebuilt for sale)

    http://skylab.org/~chugga/mpegbox/MPBS1/
    (this guy built a small one, and will sell you one, but won't give out the schematics)


    Of course, I'm sure you guys are already familiar with some of these links.
    Since I'm not an engineer, I don't know enough about circuits to build one, and I didn't think it would be that hard. But really I think it boils down to price and time investment vs. other means.

    I'm using an $80 power inverter (already had), $30 standard ATX power supply (already had), and about $15 in additional part (relays, diodes, caps). I figured out that for my system (microATX board, Athlon 900) I would need a very stout power supply (20A or more needed on 3v and 5v). The cost of the parts to build the power supply would be greater than just buying a premade or putting together the parts I had.
    Some things to think about (other than the heat that I didn't think about): engine noise (would suck to build the thing and have engine noise), power consumption when engine not running (this might not be a big deal unless you were trying to use standby mode instead of hibernate).

    I hope some of those links help. I think my system is alittle different than most everyone elses, though, since I don't have an ITX system.

    Jon

  8. #8
    FLAC
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    VW
    what I wanted was to find out was if the M-9000 would work with out the +12Volt line
    I would re-phrase the question. "Could the +12 be allowed to vary over a range of +7 to +18 without affecting the operation of the mobo. My fear is that each mobo will have a different answer.

    PHC
    I totally agree with the need for switching regulators. There are some that are very cheap & simple & efficient. Speaking of cheap and simple, here's the 12v switching regulator for Lilliput (as I'm sure you've seen). Looks like about 7 components. It uses an LM2596. You could use something similar for +5 & +3.3.
    Attached Images Attached Images  
    MikeH

  9. #9
    mst
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    Quote Originally Posted by MikeH
    VW

    I would re-phrase the question. "Could the +12 be allowed to vary over a range of +7 to +18 without affecting the operation of the mobo. My fear is that each mobo will have a different answer.

    PHC
    I totally agree with the need for switching regulators. There are some that are very cheap & simple & efficient. Speaking of cheap and simple, here's the 12v switching regulator for Lilliput (as I'm sure you've seen). Looks like about 7 components. It uses an LM2596. You could use something similar for +5 & +3.3.
    Hi Mike
    Happy New Year
    I am sorry but I have not seen the switching regulator for Lilliput before
    I am a noob)could you please post a link/information

  10. #10
    mst
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    Quote Originally Posted by VWTronics
    Of Mini-Box's web site: regarding thier PW-70A

    +5V - General M/B and disk circuitry, Memory, laptop drive motors. All Boards All our DC-DC converters have adequate power on this rail

    +3.3V - CPU core, Memory EPIA-5000, 800, V, M/1000, CL, etc All our DC-DC converters have adequate power on this rail.

    -5V - Obsolete NONE No longer needed on any boards.

    +5SB - Memory, vital sleep functions. ALL Uses little power.

    +12V - 3.5", 5.25 motors, fans, P4 power mostly P4 boards (lots of power), FET drive on all boards (little power). Use PW-60a or PW-70a only when using 3.5" drives or P4s.

    -12V - Some older serial ports EPIA-M, EPIA-M2 (EPIA-5000/800/V does not use the -12V for serial ports) Check the serial driver chipset. Modern serial chipsets do not use the -12V rail.


    As to "How is this easier than building a Sproggy?", I don't know.... what I wanted was to find out was if the M-9000 would work with out the +12Volt line, since this is the voltage that seems to give the most truble. As to easier, you could get this power supply down to 5 or 6 components and for $15-$20
    Hi VW
    Happy New Year
    I have eksatly the some question as you and have not been able to find an answer too,I guess that we will have to hook it up and try
    If the Epia needs 12v,maybe use the PW-70 for the 5 and 3.3v and get the 12v from a regulator(switching)like the one in MikeH's post;I will need 12v for my screen anyway.
    I have a PW-70 and a Sproggy kit(but are missing 2 maxim parts,on backorder
    for more then 4 weeks ;well they are cheap )but the sproggy is mush bigger then the PW-70 so I would prefer just to use that.
    PS sorry about the spelling,it is the morning after

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