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    Buckboost LED driver with TL431 or opamp in feedback loop?

    Hello,

    I am doing the following DCM Buckboost LED driver….

    Schematic:
    http://i50.tinypic.com/5yi929.jpg

    Vin = 9-100VDC
    Vout = 40 to 72VDC
    I out = 90mA


    This converter was extremely difficult to compensate.

    Would it have been easier if I had used the TL431 instaed of the LT1006 opamp?

    LT1006 Datasheet:
    http://cds.linear.com/docs/Datasheet/1006fa.pdf

    TL431 datasheet:
    http://www.fairchildsemi.com/ds/TL/TL431A.pdf

    I hear that the TL431 has a poor quality internal opamp, and I felt that this would make feedback compensation more difficult?

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    Re: Buckboost LED driver with TL431 or opamp in feedback loop?

    hi, treez

    here, I must say that the LT1006 is an op-amp and TL431 is a 2.5V voltage Regulator. You mean LT1009, I guess.
    If you, then For TL431, it is very effective voltage regulator. As my opinion TL431 can be used in this circuit.
    I suggest you to first practically run this circuit with TL431, I can say that you will not find any problem in TL431 instead of LT1009.

    And if you mean LT1006, then I have no idea about it as the two parts are different. You should go for the alternative op-amps for that.

    I hope you find the solution. I can be wrong. So look for the others suggestions.



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    Re: Buckboost LED driver with TL431 or opamp in feedback loop?

    I have to ask - why are you using an opto-coupler in the feedback loop? I see no need to have an isolation barrier when both sides share a common ground.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


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    Re: Buckboost LED driver with TL431 or opamp in feedback loop?

    Betiwt:
    why are you using an opto-coupler in the feedback loop?
    ..the reason is because the input voltage can be as high as 100V. and there is no practical way of doing feedback from this kind of voltage without the optocoupler.

    The Vin range is very wide, 9 to 100VDC, and the output voltage can be anywhere between 40 to 72VDC.

    You will see, if you approach this, that the above scematic is the best solution from cost and performance angles.

    Brathod88:
    The TL431 basically behaves like an opamp and a reference....i am wondering if it is better to just use a proper opamp likr LT1006....? (obviously then the LT1009 reference has to then be included)...............one problem with the TL431 is that it pulls one mA of current through the opto-diode resistor....i do not want this, ...there is a limit to the amount of current that can be pulled through this resistor from the voltage supplying the feedback circuitry.



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    Re: Buckboost LED driver with TL431 or opamp in feedback loop?

    You will see, if you approach this, that the above scematic is the best solution from cost and performance angles.
    It's a possible solution, but a 100V capable transistor current source would be most likely a cheaper and better performant way to span the potential difference.


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    Re: Buckboost LED driver with TL431 or opamp in feedback loop?

    FvM:
    a 100V capable transistor current source would be most likely a cheaper and better
    I take it you mean a linear supply?....not switching?.......Thanks but that would be too inefficient for us, it would give too much heat dissipation inside our enclosure......

    As sad as this has been for us, the schematic in the first post really and truly is the o.n.l.y cheap and reasonable way for this particular spec.................i am hoping that the good people will refute me and slam me into incorrectitude, but sadly you will not be able to improve on what i have provided in the first schematic



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