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PMP20058: Flyback Transformer Connectivity

J. A.
Prodigy 170 points

Part Number: PMP20058

The PMP20058 reference schematic which specifies transformer, Coilcraft Part No. UA7962-AL, has the two primary side windings connected in series.  If I am reading the transformer datasheet correctly, this provides a net inductance of 2x10µH=20µH.

I would like to use the suggested alternate transformer, Pulse Electronics Part No. PA4621NL.

Can someone confirm the connections to be used with this transformer?  To provide the 20µH net inductance, the two primary side windings would have to be connected in series, and, to maintain the turns ratio, the two secondary side windings would have to be connected in series.  Pins 3 and 2 would be connected on the primary side and pins 11 and 8 would be connected on the secondary side.

Is this how the PMP20058 testing was done with the Pulse Electronics transformer?

  • 0
    TI__Intellectual 925 points

    Hi,

    Thanks for reaching out. The net inductance on the Coilcraft transformer between pin 1 and 4 is 10uH, pin 2 and 3 are tied together in series, you can refer to the schematic's T1A connections.

    If you would like to use the Pulse transformer, the connection can be made referencing to T1B on the schematic, T1B is located to the right side of TP11, TP11 is the injection test point on the secondary output.

    Best regards,

    Max

  • 0 in reply to Xinyu Dai
    Prodigy 170 points

    Thank you, Max.  I now see the DNP'd Pulse Transformer on the schematic.

    Although, when connected this way, won't the net primary-side inductance (10µH || 10µH = 5µH) be less than suggested by the LM5022 datasheet?  The datasheet recommends targeting a ripple current of 40% for the lowest input voltage.  It seems as though it would be better to use an inductance of 20µH instead of 5µH.

  • 0 in reply to J. A.
    TI__Intellectual 925 points

    Hello,

    The way Pulse did the transformer is terminating each end of the winding on two pins, the inductance is still 10uH. Even it's two windings in parallel, the windings are wound on the same core, the inductance will be the same.

    Yes, the ripple current percentage you mentioned is correct, the percentage has to do with modes of operation (CCM/DCM), also more ripple current will result in more AC core loss, it's always a trade off.

    But I evaluated this Pulse transformer, it will work with the spec I specified on PMP20058.

    Best regards,

    Max