LM25184-Q1: PSR Flyback 120W DC-DC converter design - Transformer support

Hi Ravi,

Thank you for reaching out and considering the LM5185-Q1 in your project. This 136W design can be done but I doubt we can easily find an off-the-shelf flyback transformer to support this, but let me check with a few vendors.  I am afraid you will have to have a custom designed transformer.  Which magnetics vendors are your preferred suppliers?

Thanks,

Youhao

Hi Youhao, 

Thanks for your response. 

Currently i am working with Wurth electronic which they quoted for $3000 for transformer design. I am okey with any standard suppliers. 

As I mentioned in previous communication, I am trying to tune the secondary output2 voltage between 9V to 4V range by using some standard off- the shelf transformer ratio part to achieve this design. The secondary output2 voltage is used for micro controller and other discrete low voltage purpose so. Let me know your thoughts and suggestions. 

Regards,

Ravi 

Hi Ravi,

Sorry I cannot comment on the NRE. To my limited knowledge, the off-the-shelf flyback transformers are usually less than 100W.  I haven't seen any standard flyback transformer that could do 136W.  Let me check with another vendor, and see if they have something or able to support by doing a custom design.  

Best Regards,

Youhao

Hi Ravi,

I contacted Coilcraft and they do have an off-the-shelf high power flyback transformer FA2443 but it is not suitable to your application: It runs in CCM and the dual output windings have the same number of turns hence unable to support your 30V and 7V dual rails.  However, this transformer can be modified to fit for your application, but it also means a custom design.

Please contact tech_support@coilcraft.com and the Coilcraft engineers on the receiving end have known your case and they are happy to support you.

Good luck!

Youhao

Hi Youhao, 

This is unfortunate. Could you please suggest any other proven alternate cost-effective solutions for my requirements. If I do not find any other effective design solutions for output 30V @4A for low input voltage specified. I need to drop this flyback concept proposal due to cost constraints. Let me know your thoughts. 

Thanks & Regards,

Ravi 

Hi David, 

Thanks for your response. 

Yes, I have contacted the coilcraft team. Today i got reply saying that they are working on my request. Also, they proposed below one reference part supported for LM5185 design,

ZD2250-AE, ZE2432-AE Flyback Transformers for Texas Instruments LM5185-Q1 | Power Converter Transformers | Coilcraft

Let me know your comments. 

Regards,

Ravi 

Hi Eric, 

Fortunately, Coilcraft team responded on my request for custom design, herewith attached preliminary specifications of transformer which they proposed by confirming this they will move forward on other specification design and costing. Please review the same and let me know if you have any comments.

3581.1-1-0.2 Preliminary SPEC_Rev01.pdf2043.125W PSR Flyback--LM5185_Design_Updated_29May24.xlsx 

Thanks & Regards,

Ravi

Hello Ravindran 

I think the inputs in the excel file do not match with your component selections, especially the transformer specifications. Please double check your inputs.

-EL

Hi Eric, 

Are you pointing that given transformer schematic polarity is not matching with excel sheet derived transformer coil polarity pattern?  

(or)

The current proposed part of the transformer ratio is 1:1:0.2 for 30V @4A and 5V @ 1A, Excel sheet derived transformer ratio is 1:1:0.21 for 30V @ 4A and 6V @ <1A . Given input voltage range is 19V to 48V DC. 

Are you pointing that highlighted specification difference? I think they used my initial requirement spec 5V @ 1A in the datasheet. But for 1:1:0.2 the secondary output2 should be 6V @1W. 

Please let me know your detailed comments on shared transformer datasheet and excel worksheet. It will help me to understand and clarify the same with vendor.  

Regards,

Ravi 

Hello Ravi

Yes, that was what I found. 

Loos like the MOSFET power loss is ~6W and the diode power loss is ~ 3.5W at room temperature. Are your converter able to handle this amount of power loss at the maximum ambient temperature ? The MOSFET power loss will be even higher at higher temperature.

-EL 

Hi Eric, 

Thanks for your review, I have confirmed that the transformer design is equal to our requirements, please find the image below, 

For the MOSFET power dissipation, I have alternate solution using two MOSFET in Parallel for switching operation suggested by Youhauo Xi. Somthing like below reference schematic but not finalized. 

Let me know if you have any further comments/ suggestions

Regards,

Ravi 

Hi Eric, 

Thanks for the comments. Will you recommend any additional heatsink or design modification for the LM5185. I will follow the TI recommended Layout guidelines. 

Regards,

Ravi