This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UC2854B-EP: Is Rb1 required with the B version of the part?

Part Number: UC2854B-EP

Section 9.2.2.9 of datasheet (SGLS318A –NOVEMBER 2005–REVISED NOVEMBER 2015) discusses connecting a resistor (Rb1) from Vref to pin 6.

Page 5 of SLU177A (Revised December 2005) seems to indicate that this resistor (R11) is not required.

Could you provide some clarification please?

  • Hello Gord,

    I would say it's best practice to include the resistor. You may be able to properly bias the input if the Rvac resistor is sized properly and the Vac is properly constrained. Additionally, as per the datasheet, "The nominal voltage on ac is 6 V, so in addition to a resistor from IAC to rectified 60 Hz, connect a resistor from IAC to VREF. If the resistor to VREF is one fourth of the value of the resistor to the rectifier, then the 6-V offset is cancelled, and the line current has minimal cross-over distortion.".

    Overall you may be able to get with not having the resistor but I'd say it's best practice.

    Thanks,
    Kyle
  • Thanks Kyle.

    I should have noted that the line frequency is 300 to 900Hz not 60Hz but I don't think that will impact this resistor value.

    I will give it a try and see how the V and I waveforms look.

    Thanks,

    Gord