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UC2854: Loop Compensation in UC2854

Sundar Doraiswamy
Prodigy 30 points
Part Number: UC2854

Tool/software:

We would like clarification on the following points:
1. What is the primary role of the parallel capacitor in the UC2854 voltage amplifier compensation network?
2. If the capacitor is removed, will this compromise the loop stability, frequency response, gain margin, or phase margin?
3. Is it acceptable to remove the capacitor if testing shows improved transient performance without it?

  • 0
    TI__Mastermind 40520 points

    Hello Sundar, 

    Please read this application note concerning UC2854 design, where voltage loop compensation is discussed beginning on page 15 of the PDF file. 
    https://www.ti.com/lit/pdf/slua144 

    Your three questions will be answered, but regarding Q3: if you use UC2854 for power factor correction (PFC), transient response is limited by the intentionally low bandwidth of the voltage loop.  "Improving" transient response with wider bandwidth will result in excessive distortion of the input current, which defeats the purpose of PFC. 

    Regards,
    Ulrich