UCC28632: Off the shelf transformer

Hello Zach,

Thanks for posting your specifications, problem description concerning transformer winding customization and supply, how many designs you've tried, in addition to how you're modelling the UCC28632DR design using Webench.

Please help me understand the following two questions, so that I can provide the most appropriate response:

1. Unfortunately the reality is that custom transformers are often necessary to optimize the function of a flyback power supply for the exact specifications of any arbitrary system need. How was this controller identified or chosen for this application?
   1. It might be helpful for the customer to identify the off the shelf transformer that is best for the application first
      1. Then we can find the controller (ideally in supply) that is best suited to work with that off the shelf transformer.
   2. If need be, we can try some creative methods to get UCC28634 or any other controller working with an off the shelf transformer.
2. Can you be more specific about what is needed to pass UL certification? I'm not familiar with the exact guidelines or standards your application must design for. But if you help me understand this I think I can help you understand how to supply voltage to to the switcher IC without UL violations. 

However, I think flyback transformer vendors should not have an issue with designing something custom (it's relatively normal/standard) that does not violate UL, even in this supply-constrained environment, especially if it's in high enough volume. 

Regards,

Andrew

Andrew, thanks for the response.

1) How was this controller identified or chosen for this application?

Running through the Webench designs, I prioritized low BOM count, and then looked for controllers with good stock in the supply chain.  This part was readily available... that day.  I would be open to other designs with good part availability.

2) Can you be more specific about what is needed to pass UL certification?

Isolation.  Many transformers are built so that 8mil wide slices can be cut out of the PCB to satisfy these requirements.  

Again, I'm open to other designs, but am just looking for some assistance finding an off the shelf component that can work in one of the webench designs.  I cannot find one that recommends an OTS for what I thought would be a pretty common application (120->24).  I'm afraid the volumes for this product will not be high enough to warrant a custom part, and still stay in budget.

Hi Zach,

Thanks for explaining about how you chose this controller and UL certification. The EVM for this part uses the RLTI-1100 from Renco. I found https://www.we-online.com/redexpert/ which is an online tool from a popular transformer vendor. I haven't used this tool before so I cannot comment on how to get started with it or if it will solve your problem for sure.  

Anyways, if you can share publicly, what is the cost target for the transformer? 

Once you have a list of parts that meet your budget constraints, use relevant standards, design calculations, and performance metrics from your application to search more specifically. All of these factors are better understood by the customer. For example, use the turns ratio, inductance, currents (primary & secondary, both peak and RMS), and core shape because all of these are needed to implement the design, regardless if it's custom. In terms of standards and benchmarks, these could be isolation, EMI, thermal management, etc.

Regards,

Andrew