I'm currently designing my first DC/DC SMPS using an LT8316 flyback transformer. I am simulating via LTSpice, and am having some issues with regards to the output voltage. The transformer I am using for this is a Wurth Electronics 750311771 with a turns ratio of 6:1.

Regarding a coupled inductor for simulation within LTSpice, which values am I supposed to use. The datasheet states inductance values for the windings, but using these provides ~36V out, where I am aiming for 25V out.

However, using the formula Lpri/Lsec = (Npri/Nsec)^2 I end up with a ratio of 36:1. Implementing this into LTSpice with a primary winding inductance of 3600uH, and secondary and tertiary winding inductance of 100uH provides ~22V output. This is obviously nearer my goal, but just want to ensure I am doing this correctly!

Thanks,
Michael

 

In my collection of models for LTspice there is a specified transformer with the factory model. And many others.
Model:
.subckt 750311771_B 1 3 2 4 5 6 12 9 11 8 10 7
Lpri1 1 3 125uH Rser=225mohm
Lpri2 2 4 125uH Rser=225mohm
Laux1 5 6 13.889uH Rser=175mohm
Lsec1 12 9 13.889uH Rser=40mohm
Lsec2 11 8 13.889uH Rser=40mohm
Lsec3 10 7 13.889uH Rser=40mohm
K Lpri1 Lpri2 Laux1 Lsec1 Lsec2 Lsec3 1
.ends

 

Please post your LTspice file and I will look at it.
You are correct that you need to use turn ratio squared.

 

Hi Ron.

I have (hopefully) attached the spice file. Thank you for confirming about the ratios!

I have a feeling my issues may be to do with the diodes, but being new to SMPS I am ready to be corrected!

Many thanks,
Michael