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UC3854B Design

James Tantillo
Prodigy 40 points
Other Parts Discussed in Thread: UC3854B, UCC28070, UCC28180

I am starting a design in which I would like to use the UC3854B IC. I am getting stuck at the point in the design where it says to calculate Rimo. My issue is the power levels I am trying to use make it impractical to use a current sense resistor. Therefore I was intending to use a hall sensor and output a voltage from that to the Mult Pin.


Is this likely to cause a problem and if so how do I calculate the Rimo for this process?


In the past I have used the UCC28070 for a similar application which this is unsuitable for as I need to operate in both single and three phase. Is there something better I should be using?

  • 0
    TI__Mastermind 25570 points
    Hi James

    You could look at using the UCC28180 device. This is a newer part than the UC3854B. It is in an 8 pin package rather than a 16 pin package and is correspondingly easier to use. An advantage I see is that you could easily replace the current sensing resistor with a hall effect device because the CS input on the UCC28180 has only one function - as a current sense input. Additional advantages include the fact that you won't need to sense the line voltage.

    This would be ideal for a Hall Effect Sensor input -

    Please check that the sensor don't get 'upset' by the large initial inrush current as the line is connected. Probably not an issue, but if the sensor's magnetic core doesn't reset itself fully, or fast enough, you could end up with current measurement errors.
    They can pick up static H field effects - Earths magnetic field, Loudspeaker magnets and the like.
    I mention these only because I once spent (wasted) a day wondering why the current varied from measurement to measurement. Took some time to realise that it correlated to the sensor orientation wrt the earths magnetic field - (realisation comes slowly sometimes !)

    The UCC28180 should also run nicely on a 3 phase input -

    Regards
    Colin
  • 0 in reply to Colin Gillmor
    Prodigy 40 points
    Hello Colin,

    I was going through all the math for the UCC28180 and I see that it is looking for the Rsense value in part of the voltage and current loop compensation. If I use a hall sensor the effective resistance in that circuit is going to be zero. Is this the value i should use for the calculations? If not I need to know how to set the loops up.

    Thank you,
    Jim