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# UCC28180: Regarding boost inductor selection

Part Number: UCC28180

Hi

I am designing a 2.5KW PFC with ucc28180.

Vinmin=160

Vinmax= 270

Efficiency expected= 98

Vout= 400V

Based on a 40 percent ripple ( Inductor current) I calculated the boost inductor is 156uH.

I have the following questions

1)  Whether it is a DC bias inductance or is it a full load inductance??\

2) I have a bigger inductor which is used in another design of 600uH ( bigger core)  can carry  25A . What happens if I use this inductor??

3) basically what happens if I use much bigger inductor than calculated one??

• Hello Hema,

Thank you for your questions regarding the UCC28180 PFC controller.

For Q1:  I think it is both a DC bias inductance and a full load inductance, assuming that the DC-bias current is the peak of the input line when operating at full load and minimum input line.

For Q2:  600uH is ~4X the calculated 156uH, so ripple current will be ~10% instead of your initial 40% target.
2.5kW at 160Vac at 98% eff = 15.94Arms = 22.55Apk input line current.  Add 10%/2 to get ~23.7Apk (including ripple).  This fits within the 25A rating of your 600uH inductor.  Although 10% ripple may be good for low Differential Mode conducted-EMI noise, it will slow the ability of the inductor current to follow the line waveshape where it changes rapidly: namely around the zero-crossings.  So distortion may be higher, especially at high line (230Vac+) although I can't estimate how much higher.  Maybe not too much.

For Q3:  Scale the answer to question 2, above.  The bigger (higher value) the inductance, the lower the ripple and less ability to change current level in the inductance from switching cycle to switching cycle (mainly at low instantaneous input voltage).  The scaling should be inversely proportional.

Regards,
Ulrich