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AC-DC Isolated Power supply (5V/2A) from 3-PH 440V RMS system

Silvo Stanojevic
Prodigy 50 points
Other Parts Discussed in Thread: UCC28704, UCC28704EVM-724, LM5022

Is it possible to adapt UCC287004 to work from 3-PH 440V RMS system.  Specifically, will UCC28704EVM-724 10-W USB Adapter evaluation board work in this application assuming the AC LINE input components are rated for 1200V.  Also, a six diode bridge with 100nF bulk capacitor is used.  Would the transformer used in the evaluation board work at 600V, if not do you have a recommendation.  Would you recommend a different controller?  It has to simple as UCC28704.

Thank you for your help

Silvo

  • 0
    TI__Mastermind 31580 points
    Hi Silvo,

    Let me ask one of low power ac/dc applications engineers to look at this issue for you.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    TI__Expert 4015 points

    Hi Silvo, it probably can work, but it will not be optimised to work at that voltage. The EVM is a universal input design and as such is designed to run down to 70 - or 80V dc. Running it at 600V will mean that the duty cycles will be very short and if nothing else the efficiency will be low. You would also need to check that the inductance is high enough to keep the on time above the leading edge blanking time of the controller.

    Other than that, it should work, but as I said, suboptimally. What I would recommend doing is following the design equations in the datasheet to choose the parameter values. 100nF for the bulk capacitor sounds quite low to me for example.

     One point is that if you have a high minimum bulk voltage you can end up with a high inductance and that can lead to alot of primary turns which can cause problems. The winding resistance and parasitic drain node capacitance increase with the number of primary turns.

    There should be a referecne design with similary requeirements coming out some time in the next few months which you can refer to. Or see the following referecne design which uses an input clamp to reduce the input voltage to the flyback for high voltage applications. http://www.ti.com/tool/tida-00628 

    Hope this helps.

    Thanks

    Billy

  • 0 in reply to Billy Long
    Prodigy 50 points

    Thank you Billy.  This certainly helps.  

    While searching on TI site for high voltage power supply designs, I came across PMP7760.  Are you familiar with this design?  I am not sure if this will work for isolated power supply.  The transformer should make the output isolated from the input, note two different ground symbols.  In my case the input side would float and the output would be referenced to earth ground.  I am also concerned about the LM5022 controller performance in this situation.  The datasheet indicates min Fosc of 200KHz, however in PMP7760 Fosc=62.5KHz based on the test results ripple wave-forms.  I would appreciate your opinion on the PMP7760 design.

    Thank you,

    Silvo

  • 0 in reply to Silvo Stanojevic
    TI__Expert 4015 points

    It looks ok. The efficiency is not too bad, the output ripple looks pretty high but higher voltage rated electrolytics will probably help this.

    The IC is not limited to swtiching at 200kHz, it's just that the figures given in the datasheet don't go below that. Following the equation for the switching frequency will allow you to choose the resistance value required to set a lower Fsw.

    Thanks

    Billy