UC3842A: UC3842A

Part Number: UC3842A

I am referring to section 9.2.2 "Detailed Design Procedure" in document SLUS224E for the UC3842A device.

Equation 23 does not appear to be correct as it does not solve to the value shown in the example.

Rout is referenced in equation 23 but not defined.

Gco(f) is referenced in Equation 25, but is not defined anywhere in the document.

I would like to follow this procedure through to compensate the controller, but these issues make it difficult. Any help would be appreciated.

  • Tynmon,

    Thanks for highlighting these omissions in the datasheet.

    I will check with the original author of the datasheet and try to clairfy that section of the design example.

    Thanks,
    Bernard
  • In reply to Bernard Keogh:

    Tynmon,

     

    I checked with the datasheet author, datasheet updates are already in progress, and a new datasheet will be available online soon.

     

    The corrections for the questions above may not make it onto the next/imminent release, if not they will be taken care of at a subsequent update.

     

     

    Meanwhile, for the questions above, here are some clarifications/corrections:

     

    For eqn. 23, Rout is the load impedance, Rout = Vout / Iout. At full load, Rout = 12 V / 4 A = 3 ohm.

     

     

    Eqn. 23 has a small error, the Lpm used should be the secondary-referred magnetising inductance, or should include the term (Np / Ns)^2.

     

    Since Np/Ns = 10, the secondary magnetising inductance will be 17 uH for primary inductance of 1.7 mH.

     

    Eqn. 23 then evaluates to 9.7 kHz, rounded up to 10 kHz.

     

     

    Gco(f) is an estimate of the control (Vc) to output transfer function, where variable Q is the quality factor:

     

     

     

     

    Apologies for the confusion caused, I hope these clarifications help to answer your questions. If so, please click the "verify answer" button.

     

    Thanks,

    Bernard

     

  • In reply to Bernard Keogh:

    I tested these changes and they provide believable results.