WEBENCH® Tools/UC3845: Transformer for UC3845

Hi Jim,

Thanks for contacting us regarding your WEBENCH design.  Your output is fairly high current and probably beyond what WEBENCH would consider "standard." The WEBENCH designer algorithm designs the transformer taking into consideration several factors: maximum permissible power loss, maximum number of feasible layers, strands, etc. One or more of these parameters could not be met with your design using available core/bobbin database materials and this is why you only received limited information. I ran the WEBENCH and used 48V input and 12V/2A output just to check. Here you see much more detailed transformer design info is returned:

Since the transformer for your design is "custom", TI does not have a recommendation for the materials needed to complete the transformer design. There are plenty of excellent app notes on the internet for guidance on how to design a custom flyback transformer. 120W at 10A is a bit aggressive for a general purpose PWM like UC3845. If you're committed to the UC3845, it will most likely be challenging to optimize but 30V to 12V/10A is a sweet spot for a UCC2897a active clamp forward. If you are willing to consider the active clamp topology, TI has some nice reference designs and lots of good support for UCC2897a. Here are three reference designs I found that are close to your requirements:

1. PMP8861
2. PMP8380
3. PMP6547

If you want to try designing the UC3845 flyback transformer yourself here are a few TI magnetics references to help guide you: SLUP127, SLUP338, SLYP494.

Thanks and good luck with your design.

Steve M

Hi Steve M,

Thanks for your reply and the help. With your information i can see more possibilities in my design.

Regards,

Jim

No problem - good luck

Steve M