UCC256404: Need Help with reference design for DC DC Buck Isolated Converter I/p 40-95V DC to dual O/p 12V 120W and 24V 120W

Hello Vijay,

From your requirements you want dual output (12V and 24V).  A buck regulator will only provide a single output.  Also, Webench is only good for single output designs.  So, based on the power requirements one possibility is the forward converter with a SMPS transformer to provide dual output.  At these high currents the active clamp forward converter will be a good choice for highest efficiency.  

Looking through our Reference Designs I can see some possibilities, but they are single output so you will need to add a winding to the transformer.

PMP7451:  12Vo/10A

PMP8861:  12Vo/10A

Both these designs use the UCC2897A, which is in stock at Digikey.

The LM5025 and LM5025A are controllers capable of the active clamp forward topology.  Some of the EVMs are dual output but not exactly what you require.

Regards,

Eric

Dear Eric,

  Thanks for your quick reply! Sorry if i was not able to explain my problem properly. I need 2 different designs both with single O/p only! but both are 100W O/p's but one with 12V and other with 24V with I/p range of 45 to 95VDC. So maybe now you can suggest for 12V and 24V 2 different designs. I checked PM7451 and PM8861 both supports I/p range max till 72V DC only and my max I/p may go upto 95VDC. it will not work for me! Sorry again for not able to explain my problem clearly. Deeply awaiting your reply.

Thanks in advance!

Your's Truly,

  Vijay Gohil

Start with Webench and enter your specifications:  40 - 95V input, 12V output, 10A.  But, do not select ISOLATED.  Generate the results.  I see 79 matches.

Use the FILTERS > TOPOLOGY to select "Active Clamp Forward" and "Flyback" and "Half Bridge".  This filtering will show designs with transformer (i.e. isolation)

I see 62 possible designs.

Next I use FILTERS > IC FEATURES to select "Over Voltage Protection".

I see 4 possibilities.  Two designs use the UCC28600 but predict 78.7% efficiency.  UCC28600 is not in stock at Digikey or Mouser.

The other two designs use the UCC28740 or UCC28742 along with UCC24636 driver.  These don't predict an efficiency but considering it's a synchronous flyback I would expect it to be good.  UCC28740 is not in stock at Digikey but Mouser shows 26 in stock.  UCC28742 is not in stock at Digikey or Mouser.

You can use the same Webench procedure for the 24V, 120W design.

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Searching the Reference Designs;

I think PMP7451 or PMP8861 (based on the UCC2897A) has the basic structure you need.  It's designed for 75V maximum input, but if you understand the design I believe it could be modified to support 95 V input:  change switching FET, HV clamp, reduce switching frequency, possibly modify transformer, etc.  Power Stage Designer can help set component and system level specifications for basically any topology.

The UCC2897A has very good CAD support: here.  Simulation models and an Excel design calculator tool.

Eric

Dear Eric,

  Thanks for your quick reply... I used Webench and i made myself a design for 12V 9A design link is given below:

https://webench.ti.com/appinfo/webench/scripts/SDP.cgi?ID=C9F1C3AEF74C836F

  Now i dont understand how to make transformer and Inductor it does not tell me which core to use! can you help me how to design transformer and Inductor for the design above(T1 and L1)?

  Deeply awaiting your reply!

Thanks again in advance.

Yours Truly,

  Vijay Gohil