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Inductor and ripple current

Hithesh
Genius 3290 points

Is there a reason why I need to keep the inductor ripple current 30% (or below) of Imax ?

If I have an Inductor with high current rating, can the ripple current be 50% of Imax.

  • 0
    TI__Guru**** 191445 points

    In general, the inductor ripple current can be any percentage you want.  Originally, the percentage was set at 20-30% as it was assumed the minimum load current would be 10-15 % of full load and sizing the inductor that way will allow the converter to operate in CCM mode only (most early converters were non-synchronous).  Also, for high ESR output capacitors, ripple voltage is directly related to inductor ripple current (VOp-p = ILp-p * ESR).  Now with synchronous converters and low ESR ceramic output capacitors, that my not be a limitation.  There may be limits based on your IC.  Some have low side sinking current limit for example that could limit your p-p inductor current. 

  • 0 in reply to JohnTucker
    Genius 3290 points

    JohnTucker said:

    In general, the inductor ripple current can be any percentage you want.  Originally, the percentage was set at 20-30% as it was assumed the minimum load current would be 10-15 % of full load and sizing the inductor that way will allow the converter to operate in CCM mode only (most early converters were non-synchronous).  Also, for high ESR output capacitors, ripple voltage is directly related to inductor ripple current (VOp-p = ILp-p * ESR).  Now with synchronous converters and low ESR ceramic output capacitors, that my not be a limitation.  There may be limits based on your IC.  Some have low side sinking current limit for example that could limit your p-p inductor current. 

    One more question - 

     How will sizing the inductor all the converter to operate in CCM mode only ?

  • 0 in reply to Hithesh
    TI__Guru**** 191445 points

    If the p-p inductor current is less than twice the minimum load current, then the inductor current is always positive.  DCM is enetered when inductor current falls to zero for non synchronous converters.