What is 130 in your calculation?
Yeah it’s a smps. At some point I will release the project.
My estimate of a reliable design max Tj could go to 150°C if the divice were operated at a constant temperature. (i.e. wasn’t cycled on and off very often)
Massive SMPS design is a highly specialized field. Professionals use dedicated proprietary software and SPICE just to get started. Even electronics experts delegate SMPS design. There’s a reason only a few companies dominate the field and everyone buys off of them. I don’t mean to insult or dismay you, but your project is most likely going to explode and catch on fire if you’re struggling with heat sinks.
Sorry for my ambiguous writing. I’m not referring to the smps that handle mains voltage. I’m referring to a buck boost converter.
Send us the part number of the device or better still a PDF of the datasheet for the exact device you want to use and how you intend to use it 
Right now I can’t send it but I will send it in 10 hours or less. It’s very late.
Here is the link to the datasheet:LINK
EDIT: It should only heat up 70°C over ambient temperature
1 Like
Dissipating so much power in a diode is very old fashioned. Look into synchronous rectification. The IC’s for that probably cost less then the heat sink you need now.
1 Like
That is actually a viable option.
Info from datasheet:
- Maximum Ratings table
48A is possible provided you are able to ensure Tc=25°C. How you plan to do it? - Figure 1. With Tj=175°C (you will certainly work around such condition) and 40A you have voltage drop = 2.7V. So dissipated power = 108W. And you want 45A. Extending ch-c linearly voltage drop can be about 2.9V. So we get 45*2.9=130.5W.
- Figure 3. For 130W you have to ensure Tc below 40°C. Only little hot when inside it has Tj=175°C. It is your main problem.
Where from is this sentence/conclusion ?
I will use an active rectefier as sugested by pauldvh.
Sorry for any confusion caused
The only easy way to dissipate 10s of Watts from a surface mount PCB is to use IMS or “Insulated Metal Substrate” with the aluminium plate clamped to a heatsink
thank you for the info .
Not related to KiCad, and the discussion seems to be over.