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Original question:

TL431: .

TL431: Why REF is design to IN-

Lin_Charles
Expert 4260 points
Part Number: TL431

Hi team,

I have one question about the feedback loop? Why VREF signal apply to negative pin rather positive pin in the internal amplifier? What is the difference between these two design? Thanks. 

BR,

Charles Lin

  • 0
    TI__Mastermind 19550 points

    Hi Lin,

    The VREF is on the negative terminal for negative feedback for regulation. If the VREF is in the positive terminal it will have positive feedback which will not regulate.

    Negative feedback will lower the output voltage if its too large or increase the output voltage if its too low.

    In this situation the output of the error amplifer goes into the NPN which inverts the logic of the op amp which causes the negative feedback.