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isolated power supplies

Discussion in 'Electronic Components' started by jtm, Dec 1, 2004.

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  1. jtm

    jtm Guest

    I'm looking for an isolated 5V power supply and I don't see many available.
    (my application involves thermocouples)

    Are all "medical" supplies isolated? I saw one at Jameco (Mean Well
    MPS-30-5) that is listed as isolated but I checked the spec sheet and
    isolation wasn't even mentioned. The exact same thing with another
    "isolated" supply at Jameco: Phihong PSA15LN3-050, the specs say nothing of

    what am I missing?
  2. Johnboy

    Johnboy Guest

    Isolated usually means that the bobbin has 2 sections,
    one for the mains and the other for the low voltage. If the
    mains or the secondary short out, there will be no transfer
    of voltage to the other winding. Most metal canned xformers
    are compound wound with the primary wound first and then
    overlaid with the low voltage winding. Fish paper is between
    the windings but not always between each wind layer. I might
    be way off base with my explanation, but this is what I see
    when I have taken xformers apart to assay failures.
  3. Art

    Art Guest

    You actually could use a PC power supply with proper terminations to supply
    the isplated +5VDC source. They have available outputs of both 12VDC, 5VDC
    and many also have 3.3VDC taps. May be an inexpensive source for a isolated,
    regulated source for your tests.
  4. Hi.
    I have read somwhare that standard run-of-the-mill PC
    PSU's doesn'r work very well if not loaded properly.

  5. jtm

    jtm Guest

    That will be a problem...I'll be loading from a few mA up to an amp or two.
    I eventually want to go to production so I'll need a cheap compact unit.

    Since isolation isn't even mentioned in the spec sheets I (a relative
    newbie) figured I'm missing 'something' about isolated supplies.

  6. legg

    legg Guest

    In the spec,

    the line; "Dielectric Withstand (Hipot) Input to Output 3000VAC, 1
    min., 10mA" indicates isolation test limits.

    The isolation requirements of the labelled safety standards are what
    the product is designed to comply to.

  7. Art

    Art Guest

    Strange, seems that I did mention the PC supply being terminated properly,
    presuming you would understand that is indicative of proper loading of the
    item to regulate and operate correctly. But you apparently love a chase so
    go for it, I'm confident that you will find a commercially developed 5VDC
    regulated and isolated supply eventually, and pay a fair price for it.<
  8. Eric Smith

    Eric Smith Guest

    Any AC-mains-input DC-output power supply you would buy from normal
    sources, switching or linear, is isolated. However, there is still some
    leakage current. Medical supplies have a lower maximum leakage current
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