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+/- supply frm single chip

Discussion in 'Electronic Basics' started by [email protected], Aug 19, 2006.

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  1. PeteS

    PeteS Guest

    wrote:


    why sir???dnt we hv any chip for this ??

    [ Middle posting ;) ]

    What you apparently want is to go from 20V (whether AC or DC has not
    been specified] to 3 outputs:

    +5V, +12V and -12V

    Assuming it's 20Vdc in, there may be triple supply switchers out there
    that can do buck and invert in the same device, but I personally don't
    know of any (and I don't feel ike looking through catalogues on Sunday
    either).

    Alternatively, you would be looking for a dual linear with a switched
    cap inverter (not a particularly good choice for precision electronics,
    incidentally), and once more I don't know of any.

    Given that using switchers will necesssarily increase your component
    count by a minimum of two inductors, you would be better off using 3
    devices with the associated input and output caps (which you will need
    with any supply).

    If your input is AC, you'll need a rectifier in front of it as well (as
    all the others here could tell you).

    Txltn:
    Wht u apprntly wnt is 2 go frm 20V (whthr AC or DC hs nt bn spcfd] 2 3
    otpts:

    +5V, +12V -12V

    Assmn it's 20Vdc in, thr my be trpl spply swtchrs avlbl that cn do bck
    and nvrt in th sm dvc, but I prsnlly dnt knw of ny (nd I dnt fl lk lkng
    thru catlgs on Sndy ethr).

    Altrntivly, u wld be lkng 4 a dl lnr with a swtchd cap nvrtr (nt a
    prticly gd chce for prcsn lctrncs, ncdntly), nd once mre I dnt knw of
    ny.

    Gvn tht usng swtchrs wll ncsarly incrs ur cmpnt cnt by a mn of 2
    ndctrs, u wld be bttr ff usn 3 dvcs with th assctd npt nd otpt caps
    (whch u wll nd wth an spply).

    If ur npt is AC, u'll nd a rctfr in frnt of it as wll (as ll th othrs
    hre cld tll u).

    Cheers

    PeteS
    (Practicing language skills)
     
  2. John Fields

    John Fields Guest

     
  3. Guest

    So i think it'll be better for me 2 use 7805,7812 & 7905...instead of
    searching for a single chip....thnx for help

     
  4. Eeyore

    Eeyore Guest

    *Why* FFS does it have to be *ONE chip* ?

    Graham
     
  5. Chris

    Chris Guest

    A while back, there used to be linear regulator ICs which would provide
    a tracking split supply. However, they required extrernal transistors,
    and other components.

    The 78XX and 79XX regulators are simplicity itself, and due to volume,
    they're incredibly inexpensive. If they do the job, why not just use
    four TO-92 or TO-220 packages?

    By the way, please bottom post. Since you're a Google person, please
    read Google Groups Help Topic "What's good 'netiquette' when posting to
    Usenet?"

    http://groups.google.com/support/bin/answer.py?answer=12348&topic=250

    Good luck
    Chris
     
  6. I'm curious. Would it be possible to use a voltage divider and an
    optoisolator to get the +/- supply?
     
  7. Eeyore

    Eeyore Guest

    NO
     
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