inductor LNK PH buck, gap length

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Hi,

 

I´m desiging a LNK PH buck inductor and hava a basic question.

The specs of core EE20-10-5 are: AE=0,31Cm2; LE=4,3Cm; AL=1300nH/T^2. 

Vin: 190 to 204V

vout: 60V@830mA 

Using a KP of 0,81 result in 482uH, 140 turns, gap lengt of 1,5mm.

But, the necessary gap lengt to obtain 482uH was 2mm.

In your practice, this values of 2mm or 1,5mm are too big values or are "normal" valures for a gap in a ferrite core? 

 

If  I use kp=1 the the peak current increase from 2,16A ( for a kp of 0,81) to 2,28A ( for a Kp=1). And of course, the inductance is lower, 328uH, less turns and lower gap.  do you think that this difference of 120mA ( 2,28A-1,16A ) is an important "improvment" in this design or no?   The current limit of lnk409 is 3,12A.

 

Thanks. 

Hi,

The calculated and actual air gap varies according to the core material.   Key in the actual "Ungapped Core Effective Inductance" (AL) in the spreadsheet calculate the expected air gap.

 

For LNK-PH, <1 KP is recommended for optimum power factor, but if you have enough design margin then you can operate close to 1.  This will benefit the transformer but the effective RMS current on the device will go up.  Test for the two values you have calculated to get the optimum efficiency.

 

 

Regards,

PI-Jono