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TL431: Open loop gain?

Anonymous
Anonymous
Guru 17045 points
Part Number: TL431

What is the open loop gain for the TL431 op-amp i.e. is it like a unity gain difference amplifier working to keep feedback voltage at ~2.5V or ~1.24V depending on the version or does it have very high gain and is working in that way to keep the two the same?

  • Hi Handy Andy,

    The feedback voltage is compared with an error amplifier to a bandgap reference of the TL431 (2.5V). The amplifier is used to correct the cathode voltage such that the feedback voltage will be as close as possible to 2.5V.

    As for the gain specifications, this not something we have readily nor give out.

    Let me know if you have anymore questions.

    Ethan
  • Anonymous
    0 Anonymous in reply to Ethan T
    I noticed in the datasheet that the bandgap voltage reference is connected to the inverting input of the afore mentioned op amp and the feedback is taken at the non-inverting input. How does this not make it a comparator(in closed loop mode) or else lead to oscillations i.e. how is it negative and not positive feedback?
  • Hi Andy,

    The error amplifier generates an error voltage (difference between output reference and the internal reference). By design specifications, the error voltage outputs to transistor networks which controls the desired cathode voltage.

    In a positive feedback network, the output voltage is dictated by the polarity of the non-inverting input. Since the non-inverting input is a positive voltage, the amplifier will drive its output positive up to positive saturation voltage. Since the saturation voltage is the cathode voltage, the FB voltage will be at 2.5V.

    Hopes this adds some clarity.

    Ethan