UCC28950: Need Design and TINA TI simulation support

Hello,

I am reviewing your inquiry and will get back to you shortly.

Regards,

Hello,

When I look at your waveforms the output seems to be decaying from 12 V and the duty cycle looks to be 0%.

If your resistor divider is set for 48 V you should be demanding a 100% duty cycle.  I would start with checking your voltage feedback to make sure it is setup correctly.  In SLUM277A this is resistors R6, R7, R1, R2, R9, C3, and C4.  SLUM277A was designed for a 12 V output and since your output is not going above 12 V this could be part of your issue.

The other issue that you could be having is your transformer turns ratio may not be correct as well.  You may want to check that as well.

The following link will bring you to an application note showing on how to design with the UCC28950 in a phase shifted full bridge.  This information was used to design the SLUM277A 600 W design.  There is a link to an excel design tool within the application note that uses the same calculations that in the application note.  I recommend using the application note and excel design tool to check your design and calculations. Then fixing your design if necessary and rerunning your simulations.  https://www.ti.com/lit/pdf/slua560

Regards,

Hello,

Do you have any further questions?

Regards

Hi Mike O' thank you very much for your response. In SLUM 277A, I have recalculated all the design parameters and verified them with the excel design tool. But still I am not getting the required results. Transformer turns ratio also verified. What would be the issue. 1.How can we select  R2 and R6 resisters? 

2. How to give load resister value for Po=1kW and Vo=48V in the below figure.

Hello,

I am reviewing your inquiry and will get back to you shortly.

Regards,

Hello,

Could you send me the excel and tina file?  I would like to review them.

Regards,

1kW_DC_DC_Design.xlsx

Hi Mike O' thank you very much for your response. Please find the Excel file and TINA File. Still I am getting below results. Not required one.

4503.1kW_DC_DC_Design.xlsx

48V dc_dc 1kWPSFBSR.TSC

Hi Mike O', can you share UCC28950/UCC28951 TINA-TI Transient model (SLUM278A.ZIP (98 KB) - TINA-TI Spice Model).

I am unable to open (After extracting Zip file) SLUM278A.ZIP (98 KB) - TINA-TI Spice Model (Transient model). It would be helpful for my design verification. 

Hello,

I am reviewing your inquiry and will get back to you shorlty.

Regards,

Hello,

I reviewed SLUM278A and agree with you the file is not loadable.  This model should not have been released and I am going to request that it be removed from ti.com.

In regards to the transient tina model.  The SLUM277A.TSC tina startup model is the transient model.  We also have a released version in PSPice model of it SLUM169.  https://www.ti.com/lit/zip/slum169

Sorry for the inconvenience in regards to the non working model.

I am still reviewing your excel file and tina model and will get back to you shortly.

Regards,

Hello,

I just wanted to let you know that I am still working on this.  I modified SLUM277A based on your excel design file.  I have attached it for your reference.

48 V 1 kW DC.tsc

Transformer T2 was modified to have a turns ratio of 3:1 and a Lm of 3 mH similar to what you have in excel design file.

I ran the simulation and even though transformer T2 is set to 3:1 it actually 291.94V/38.91V = 7.5:1.  For some reason the model will not allow this to be modified for 3:1.  This is why your output in your simulation does not come into regulation.  Please see the waveforms below.

In regards the CS waveforms for this design they do not look correct also for a phase shifted full bridge.  I am going to contact the modeling team to see if they can look further into this for you.

In regards to designing the PSFB using the UCC28950 many applications engineers since 2010 have found application note slua560 and the excel tool reference helpful in doing there designs.  You should be able to continue to use these tools to design your power converter.

https://www.ti.com/lit/pdf/slua560

Regards,

Hi Mike O' thank you very much for your response. I referred your modified design.

1.The output voltage is not varying even by varying the input voltage (210V to 410V).

In modified simulation the output is not regulated at 48V. And the output is decreasing from 41V. It is not constant. 

2. In modified design the leakage inductance is considered as 90uH. How it is taken and while calculating the tank frequency, what will be the  shunt inductance (Ls)?

Why we need to chose 90uH leakage inductance?

Hello,

I received you inquiry and it is under review.

Regards,

Hello,

The leakage inductance of the transformer is generally 3% of the magnetizing inductance and is why 90 uH was chosen for the leakage inductance in the transformer.

There appears to be something wrong with the Tina transformer model and that is why the output is not coming up into regulation.  As you pointed out the transformer should be stepping down the voltage 3 to 1 and it is not.  I found this to be the case as well.

I am forwarding this inquire to the PSpice TI modeling team so they can help you get the issue with the transformer model resolved.

Regards,

Design Soft may be able to provide more details on the transformer. 

what type of transformer details are required?

There is no regulation is happening even by varying the transformer turns ratio and input voltage.

Mike,

I simulated the SLUM277a reference design and was able to observe continuous change in VM1,VM2,VM3 and VOUT as the transformer ratio changed all the way to 1:1

I did not make any other changes to the load or stimulus. Is it possible that Sugali's desired circuit is outside of operational specs for the UCC28950 and that those limits are part of the model?

David

Hi David, Thank you for your response. After changing the transformer turns ratio as 1:1:1 also no variations in my out put. 

Hey Sugali,

Yeah, I didn't expect that to work given prior efforts. That's why I was asking Mike if the model has some hard limits.

David