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UC3854A: Current sense resistor selection

C.S.
Prodigy 60 points
Part Number: UC3854A
Other Parts Discussed in Thread: UC3854,

Tool/software:

We are building a circuit based on the UC3854. Input current up to 20A, will result in a substantial dissipation on the current sense resistor.

Normally for the smaller converters metal film or wirewould is used, but I am aware some of these resistors may not necessarily be 'non inductive' and it becomes hard to source the correct type. Are there any recommendations for resistor types that would be more suitable and inherently non inductive by design?

Thanks

  • 0
    TI__Mastermind 38990 points

    Hello C.S. 

    Thank you for your interest in the UC3854 PFC controller. 
    May I suggest to consider UC3854A or -54B as an upgraded close alternative.  They are nearly the same as UC3854, but have a several improvements to make it easier to design. 

    Non-inductive resistors suitable for high-current current sensing can be found by searching distributors' websites (such as Arrow, Digikey, Mouser, etc.) for "current sense". 

    To avoid the high dissipation of a current-sense resistor in high-power PFC designs, a pair of current-sense transformers (CT) can be used to reduce the power considerably. 
    One CT is placed in the MOSFT drain path and the other in the output diode path.  
    Refer to this App-note, on pages 3-279, 3-280: https://www.ti.com/lit/pdf/slua144 

    Regards,
    Ulrich