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    Toroidal O-CORE Power Transformers


    O-Core power transformers are the preferred choice for applications when a lowest possible profile is a design priority.  O-Core transformers have a diameter to height ratio of around 3:1 compared to 2:1 for our regular toroidal cores.

    Since O-Cores have no sharp edges they require less insulation and can be wound with less fill factor resulting in a lighter and smaller transformer than a regular toroidal core transformer.

    The grain oriented silicon steel properties of O-Cores are the same as in our regular toroidal cores giving the O-Core transformers the same electrical benefits. They can be used in designs for the same applications.

    If your design requires a narrow footprint our regular toroidal core is a better choice as it offers flexible dimensions.

    O-Cores are wound from a steel strip which is continuously pointed towards each end to produce a circular cross section. The circumference of a circle is about 12% less than that of a square with same area and 18% less than a rectangle with the same area and a diameter to height ratio of 2:1 as in the typical regular toroidal core transformer.

    Please refer to the chart below for the physical sizes of power ratings up to 2,000VA 60Hz, or 1600VA for 50/60Hz frequencies.


    O-Core Transformers
    Size and weight of different power ratings
    VA @ 60Hz
    VA @ 50/60Hz

    OD x Height    OD x Height
    (inches)             (mm)

    Lbs          kg

    45 36 3.0x1.0 76x24 1.2 0.5
    65 52 3.2x1.0 80x26 1.4 0.6
    90 72 3.4x1.1 86x28 1.7 0.8
    115 92 3.7x1.2 93x30 2.2 1.0
    175 140 3.9x1.3 99x32 2.7 1.2
    220 176 4.2x1.4 105x34 3.2 1.5
    275 220 4.5x1.4 113x36 3.8 1.7
    320 256 4.6x1.5 116x38 4.2 1.9
    425 340 4.9x1.6 124x41 5.2 2.4
    550 440 5.2x1.7 131x43 6.1 2.8
    650 520 5.4x1.8 138x45 6.8 3.1
    800 640 5.7x1.9 144x49 8.5 3.9
    1000 800 6.0x2.05 152x52 9.8 4.5
    1300 1040 6.3x2.1 159x54 12.5 5.7
    1600 1280 6.7x2.3 169x57 15.0 6.8
    2000 1600 7.0x2.4 179x61 17.5 7.9

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  • For 50/60 Hz operation, the listed power rating is reduced by 20%.
  • Dimensions and weight are based on single primary and single secondary windings.

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