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UCC28180: PFC Design Questions

gene glick72
Prodigy 100 points
Part Number: UCC28180
Other Parts Discussed in Thread: , LMG3410R150

I noticed on the UCC28180 data sheet that there is a single diode in the sample circuit. On the UCC28180EVM-573, there is an additional diode connected to the line side of the boost inductor. I've seen this elsewhere too, but do not understand what it is used for. Can you provide some insight?

  • 0
    TI__Guru 65965 points

    Hello,

    This diode is for inrush current and used to protect the boost FET from inrush current.  The UCC28180 controller is not fast enough to protect the FET from inrush current.

    The other think that the diode does is it prevents the LC in the stage from ringing up to 2X the line voltage.  If you do not use this diode this can happen.  Please use the diode in your design.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 100 points

    Thank you.

    I expect that this inrush protecting diode does not need to be anything special other than voltage - while the boost diode does need to be special, maybe SIC. Is that correct?

    I have noticed as well, that some folks use an additional smaller inductor prior to the main inductor. These designs take the inrush diode from this location. I'm sure there's a reason for this - do you know of such designs?

    The plan is to run this PFC at 200 kHz. Do you see any downsides? The chip will do it, SIC diodes should be fine with it, I'm not certain about the main MOSFET but would consider using GaN if that helps.

    best regards,

    gene

  • 0 in reply to gene glick72
    TI__Guru 65965 points

    Hello,

    The inrush diode does not need to be anything special. It does not have to be SiC and can be a fast recovery diode.  The diode does need to be rated for the maximum inrush current.  Typically an NTC is used to limit the inrush current as well.

    I have not seen design uses a smaller inductor prior to the PFC inductor.  Are you sure this is not part of an EMI filter?

    Using SiC diodes for 200 kHz is a good choice due to the low reverse recovery current.  I had done 200 kHz PFC designs with SiC diode and Si FETs and was quite efficient.  You can use GaN FETs that switch 10 times faster compared to Si.  Which means the switching losses would be 1/10th and could be a good choice for your design.

    The faster switching speed of GaN means that they layout is more critical.  Every inch of trace is roughly 10 nH of inductance.  TI GaN devices data sheets give recommended layout techniques to be followed if you decide to use GaN devices.

    The LMG3410R150 is a popular FET for PFC applications. The follow link will get you to the data sheet.  Section 11.2 gives very detailed instructions on how to layout the board using GaN; as well as, an example layout.

    If you have any problems or have any questions about using TI GaN, please repost to the e2e with the GaN part number in the heading and the appropriate applications engineer will help you with the design and use of the GaN FETs.

    Regards,