UCC28070: SLUC114a

Hi Jasvant,

Thank you for the query on UCC28070.

The design tool only makes sense for a universal input of 85V to 265V rms and output voltage of 400V.  Selecting the inductor size based on K(D) as the application note/calculator shows for a limited input range does not make sense.  The maximum inductor ripple current occurs when the duty cycle is at 50%.  This is where you should select your inductor. 30% inductor ripple current is normally recommended at this point.

You an calculate L and delta(IL) as follows

D=50%

Change IL = (((Pout/2)*1.414)*0.3)/Vinmin

Lboost= ((Vboost/2)*D)/(Change IL*Switching Frequency)

You might have to do these calculations by hand and then manually input these values into the excel calculator for the rest of design.

Regards,

Harish

Hi Harish,

Really appreciate your quick response, Thank you.

Can you please provide the source material for the formulas you have mentioned?

I just want to be sure about parameters, constant and units being used in formulas.

Regards,

Jasvant 

Hi Jasvant,

The above equations are normal boost pfc (boost converter) equations. You can refer to the following application notes:

1. https://www.ti.com/lit/an/slua479b/slua479b.pdf?ts=1671729333850&ref_url=https%253A%252F%252Fwww.google.com%252F

2. application note AN5298 page 21 for the equation of peak current of PFC

Thank you

Regards,

Harish

Hi Harish,

Thank you for the reply.

I was already using slua479b as reference that's why I referred related slua114a spreadsheet but faced problems that I mentioned in earlier post in this thread.

Just to confirm some points about the formulas that you have provided earlier in this thread -

1. did you miss efficiency term in formula of delta (IL)?
2. To calculate delta (IL)and L, should we use minimum input voltage or typical input voltage?

• Also please provide the link for AN5298 so I get the correct document which you are referring to.

Thanks,

Jasvant

Hi Jasvant,

Please check the following link page-21.

https://www.st.com/resource/en/application_note/an5298-stevalipfc12v1-2-kw-two-channel-interleaved-pfc-with-stnrgpf12-digital-controller-featuring-inrush-current-control-stmicroelectronics.pdf

Efficiency can be included as you suggested. The inductance is calculated at minimum input voltage as shown in app note above. (But you could take an average as shown in the calculator).

Thank you

Regards,

Harish

Hi Harish,

Thanks for the reply.

To calculate average value of the Inductor, we need maximum value of the inductor. Can you please let me know how to calculate the max value of the inductor because there is no formula for max value of inductance in slua114a calculation sheet.

Regards,

Jasvant

Hi Jasvant,

There is no formula here. You should be ok with a value greater than or equal to the minimum recommended value.

Regards,

Harish