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Stability analysis for hysteretic switched mode LED driver?

Discussion in 'LEDs and Optoelectronics' started by eem2am, Apr 21, 2014.

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  1. eem2am


    Aug 3, 2009
    Can you confirm that a Bode plot stability analysis for a switched mode LED driver based on the ZXLD1360 IC (schematic as per page 2 of the datasheet) is pointless?

    That is, ZXLD1360 based LED drivers are intrinsically unstable, its just that the instability is bounded by the comparators?
    So can you confirm that the phase and gain margins (if produced) would indicate instability, and so would be pointless?
  2. Arouse1973

    Arouse1973 Adam

    Dec 18, 2013
    I don't quite follow. You don't produce phase and gain margins the gain margin is the amount of gain you can add to lift the 0dB point to the same frequency as the -180 degree crossing point. Phase margin is the difference between the actual phase and -180 degrees. An open loop opamp can be unstable and we tame the gain by adding negative feedback. What's the difference in doing this with the comparators. But if there is no way of changing the gain margin and you don't have a very large phase margin because of the circuit then I suppose it is pointless, You could do a Nyquist Plot just for fun if you wanted to prove it.
  3. eem2am


    Aug 3, 2009
    My apologies, I meant "calculated", not "produced".
    I believe the phase margin for the hysteretic led driver would be zero degrees?.....and the gain margin would be zero also?....after all, as you know, the hysteretic converter is basically an oscillator.
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