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UCC28950: Help to fix problems in circuit

Part Number: UCC28950

I have not enough experience with DC/DC. I have to fix problems in power supply. Circuit diagram attached.

I am not developer of this circuit. Input voltage for power supply is 24V output must be 48V.

At this time feedback doesn't work correct. Output voltage without load is about 70V, with 50% load output voltage is 37V.

I have lot of questions. I will start from first question.

I want to check all values used in design. To very calculations I use mathcad and UCC28950 Design Tool _sluc210D.xmcd file.

In all designs which I see input voltage is higher than output. In my case output voltage is higher than input.

I have problems with calculation Dtyp value.

Dtyp=((VOUT+vrdson)*taa1)/((vin-2*vrdson))

where taa1 is Np/Ns for me it is 2/3 (transformer Wurth 749251020)

Dtyp = ((48+0.3)*2/3)/(24-2*0.3) = 1.37

Maybe this equation is correct only for step down converters?

 I have to use another equation for step up?

UCC28950.pdf