WEBENCH® Tools/UCC28C45: DCDC-Flyback-Converter: Webench creates CUSTOM transformer which cannot be bought

Hi Wolfgang, 

Thanks for using WEBENCH Power Designer, WEBENCH algorithm supports in-detailed transformer selection(which includes core/bobbin selection, wire gauge, number of turns/layers/strands, etc that is required by the transformer vendor for its construction) for single output fly-back designs, for most of the operating conditions. 

In some cases, however it might not be able to give those details if we do not have enough core/bobbin in the database which are required for satisfying all conditions which are required for giving a good transformer design. One such case I have seen is when the user operates the fly-back at high frequency ( >=500 k)

For your question on existing buyable components for off shelf transformer, our database has some of those as well which gets designed too based on the operating condition. The power stage in fly-back is targeted in WEBENCH to give an optimum design(w.r.t stresses on primary FET/sec diode/pk currents). We can always change the power stage design by adjusting the duty cycle/turns ratio, that can help in getting an off the shelf transformer, however that might not give us overall good design. Currently we can not change the operating duty cycle in the software, which can actually help in redesigning the whole power stage/and may be also give an off shelf transformer in this process.

Can you help me give Vinmin, Vinmax, switching frequency for your design, so I can test it out. You can also share the design here, if possible. 

Thanks

sahil

Hi Sahil,

Thanks for reply, that sounds hopefully, indeed.

I could forward the pdf printed case and additionally the transformer I wanted to use because it is off the shelf and fits to my output values.

My input values are 37V thru 57V DC, output Voltage should be 24V, output current at 2.2 to 2.5A. I have to separate primary and secondary side to get isolation. Therefor I would need some kind of transformer in.

I have several possible transformers that I could try, POE62F-24ED or POE71F-24ED, because they already have specified the output voltage as 24V, even the current is ok. Here's the link to the datasheet: https://www.coilcraft.com/poe62f.cfm .

UCC28C45_24V_2.2A_2.pdf

Hi Wolfgang, 

I checked the WEBENCH transformer for your condition, I will recommend to lower the switching frequency to bit lesser value like 95 k instead of 100 k(current design), if that works fine for you, from the advanced options in the WEBENCH dashboard window.

you will be able to get the complete transformer design, which you can share with the transformer vendor, if that works good. 

i am sharing the design report here( contains transformer report as well), 

xformer report.pdf

For the transformers POE62F-24ED or POE71F-24ED,  the only issue i see is with the Isat value - they have it close to 6 A, however with the power level of your design and the operating duty cycle(~36 percent, the maximum what this IC can support is 47 percent), the primary pk currents in the design go up to close to 9 A. 

If we want to use the 6A transformer , then we might have to increase the duty/change the primary current ripple, which will lead to change in complete power stage design furthur.  

Perhaps we can operate the design at slight lower frequency(~95 k), and then check if everything works fine. 

let me know if anything here, 

Thanks

sahil

Hi Sahil,

Thanks for your kind efforts, that is really great.

To answer the questions: I am not fixed to a special frequency, so 95 kHz is ok for me as it would be with the others. This was just a proposal Webench provided  to the user (me).

The transformer is pretty large. I checked the Würth page for data and found that the core is already more than double the volume of the proposed POE62-transformers. This one I chose of it's low height because in the design there will not be enough space, because I have to build in more boards.

Anyway that's a start. Where can I get access to that transformer builder SW? I didn't find it in my Webench account.

Another question: Can you tune up the frequency for then I guess we'll get a design with a lower volume transformer? Maybe that would be a total new design. I got this idea some days ago already when I read the transformer's datasheets, which say that the POE62 etc. are measured at a higher freuquency of 250kHz.