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LM5021-Q1: entrered above

Keith Johnson3
Prodigy 90 points
Part Number: LM5021-Q1
Other Parts Discussed in Thread: TL431

Does not Load regulate. See attachachmentLM5021 TI Question 2.docx

  • 0
    TI__Mastermind 31580 points

    Hi Keith,

    You will need to provide a separate bias rail for the feedback circuit in the real application, like a 12V rail. The TL431 will be fail due to an overvoltage stress if it is configurated in the same manner as the attached circuit. RLED and RBias will also have high power dissipations.

    When the voltage on your Vout potential divider 1780k/10k hits 2.5V the TL431 should start to shunt current, so the voltage on the cathode should fall, you should also see a voltage drop across Rled.

    Once the TL431 shunts current the FB voltage should fall and start to modulate the duty cycle.

    Note that the TL431 reference pin has an input bias current spec so this will also cause an addition error term in the output voltage setpoint.

    Regards

    Peter