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28019 pfc waveform and support discussion request

Eric Gustafson
Prodigy 30 points
Other Parts Discussed in Thread: UCC28019

28019.pdfI would like to discuss my implementation of a 28019 pfc.  This application is a brushless motor drive, and runs at 1kW.  (Working on this type of circuit 10 years ago, I was able to discuss with Dave Parks of TI – but I imagine he is retired by now.)

In the attached pics (a pdf) you can see the AC input current waveform.  Seems it could be a bit better.  I have followed the sluc069d.xls calculator including the m1m2 portion.  Some questions:  How can we improve the AC line shape a bit?  Min bus cap size possible (push until output voltage feedback gets tricked – other penalties of that?), My ac input filter is a bit unique due to other product requirements – can send schematic.  Would like to discuss EMC tips and pointers prior to prelim EMC lab trip.

  • 0
    TI__Mastermind 31580 points
    Hi Eric,

    I will get one of our engineers to contact you.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    TI__Mastermind 34465 points

    Please attach a pdf copy of the schematic and BOM so that we may gain further insight into your design

  • 0 in reply to John Griffin1
    Prodigy 30 points

    pfc-sch-march-2105.pdf

    John, here is a schematic.  I don't have a complete BOM laid out for this proto yet, but here are the highlights.  one unit has diode stmicro stth12t06, mosfet ipp60r190p6, inductor micrometals t175-60 wound to 1.0mh.  A second unit with diode cree c3d06060a, same mosfet, and inductor micrometals t157-60 wound to 1.5mh.  These parts are all a bit big, but its a starting point.  I'll need to do some cost reduction.

    The most odd thing about this schematic is that our device is two speed - and this is accomplished by having two paths to feed ac to the system.  So the line filter is place on the dc side of the bridge, so it can filter either ac feed.  This may be effecting the shape at pin 4, Vin.  I should have some prelim EMC results this week. 

  • 0 in reply to Eric Gustafson
    TI__Mastermind 34465 points
    Hi Eric,
    One think I notice is that you have two common mode inductors after the bridge rectifier.
    Normally the common mode filter is place on the AC side of the bridge. This is because the rectifier is usually a big part on a large heat sink . This means that it has a nasty habit of being a source of EMI either through a parasitic ground path or directly through radiation from the switching MOSFET and main diode.
    So if at all possible I would consider placing one of each common mode chokes on an AC input line.
    Then on the DC side of the bridge rectifier, your EMI results will benefit from a small differential mode inductor (say 100uH). These will also help to improve the shape of your input current.
    The smaller you make the bus capacitor will degrade the shape of the input current . The lower limit of the bus capacitor is set by its ripple current handling capability.
  • 0 in reply to John Griffin1
    Prodigy 30 points

    prelim emc result.pdfJohn, Thanks for your comments.  I have attached some preliminary EMC results.  This is our device in high (about 950W) and low (about 50W).  Not to bad for a first pass in my mind.  We will try some of the configurations you suggest.  Our bride is not heat sink mounted.

    If I am trying to minimize the boost inductor size - what will be my penalty?  Less inductor = higher currents, any tips beyond that?

  • 0 in reply to Eric Gustafson
    TI__Mastermind 34465 points
    It is important that the UCC28019 remain in CCM mode. If you use the calculator it will recommend an inductor value that will maintain CCM .
    Using a lower value of inductance causes the power supply to operate in DCM mode. PFC and harmonic distortion will increase and EMI will be worse.