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Thread: simple 12v,5v,-5v,-12v power supply

  1. #1
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    simple 12v,5v,-5v,-12v power supply

    if i have an input of + and - 12v and ground, whats the simplest way to get +12v, +5v, -5v and -12v? with a regulator.

    edit: this is for a PC supply, so i needs to be 2A?

  2. #2
    Constant Bitrate GRUNT's Avatar
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    Have a look at the Power Supplies section.
    Or search for DC-DC.

    Your looking for 12v DC-DC power supply.

  3. #3
    jol
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    FLAC jol's Avatar
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    I'd say that a sproggy psu would be the easiest way. Get a semi-kit from mastero and the rest of the parts from renco and maxim, more resellers too.

  4. #4
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    ok, ill do a search.

    i want to build one so i want a circuit diagrma, not a kit

    for an old PC, a 486 for example, how much current for the +12v and +5v supplies do i need?

    if i have a 1A regulator, can it regulate higher currents if i keep the chip cool? with a huge heat sink and fan(s).

    how do i get 3.3v? and do i need it?

  5. #5
    Maximum Bitrate eugenen's Avatar
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    The amount of current all depends on the components. Old hdd's can draw an amp on the 12v line but a laptop hdd may draw max of 1/2 amp on only the 5v line. An old 486 won't need 3.3v but may take 5a on the 5v line. You can't run a regulator over its spec, most have overload and thermal shutdowns inside them.

  6. #6
    Variable Bitrate spud42's Avatar
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    but you can use a power transistor as a current bypass and use the voltage regulator as a reference to it. ie using a 2n3055 and a 7812 you can get a 3 a 12v psu......... circuits should be on any site with basic electronics....
    Volvo V40 Phase 2 2002. T4 turbo upgrade.... currently no mp3 or carputer..... researching options

  7. #7
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    Originally posted by spud42
    but you can use a power transistor as a current bypass and use the voltage regulator as a reference to it. ie using a 2n3055 and a 7812 you can get a 3 a 12v psu......... circuits should be on any site with basic electronics....
    any links? i have some 2n3055's.

  8. #8
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    can i use this website? voltage regulator

    and is the MJE340 the same as the MJE34?

    if not, which of the following can i use instead of a MJE34?

    BD132
    BD140
    BD712
    MJ2955
    TIP32A
    TIP32C
    TIP36C
    TIP42A
    TIP127
    TIP147
    TIP2955

  9. #9
    Raw Wave Rob Withey's Avatar
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    This took me about 2 minutes to find with Altavista:

    http://www.repairfaq.org/sam/samschem.htm#schslp2
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  10. #10
    Raw Wave Rob Withey's Avatar
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    Here are more:

    http://www.mitedu.freeserve.co.uk/Ci...wer/boosti.htm
    http://www.chantronics.com.au/Data/V...regulators.htm

    This one is for a regulator with feedback (and adds headroom requirement due to the additional Vbe drop).

    http://dbserv.maxim-ic.com/appnotes....ote_number/295
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

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