Off line SMPS transformer selection

[Joe Voytovich]

I trying to replace a linear supply on a new design with a switcher. It will be marketed overseas, so it will see 110/220, and a switcher can handle that without any jumper changes.

I've got a few designs in mind using Fairchild ICs, but the one problem I have now is finding a matching transformer. I saw a demo board on their site that has a BOM with a transformer listed from SEN HUEI INDUSTRIAL, but no luck finding them.

What is a typical source for these parts? The demo board shows transformer specs for windings, wire size, etc. Are these parts custom designed or usually off-the-shelf?

 

[Dan Mills]

Usually custom, but Wurth/Midcom spring to mind as having a small selection of off the shelf switchmode transformers, nothing very sophisticated but useful for the simpler sort of smpsu.

I strongly suspect you will either have to design a switcher around the available magnetics (Sometimes viable in small quantities) or use a custom part.

Regards, Dan.

 

[Joe Voytovich]

Thanks Dan. I did recently find that some coil companies have stock parts that will work with specific ICs. They do list those so they're easy to find. Wurth is one. I also found Precision Inc makes some for Power Integrations (among others), and Coilcraft makes some for ON Semi, Linear and TI.

What I'll probably do is pick out some ICs that might work, then contact the companies to see if they have any vendors that make coils for those parts.

Wondering... instead of putting in an SMPS with crazy tight regulation (and more costs), would it be cheaper to have the switcher put out 7V with a little less regulation and use an LDO to get the final voltage? That way you wouldn't have to worry about any hash or spikes slipping though on the switcher output.

 

[Dan Mills]

Linear post regulators are reasonably common where the eventual load is sensitive analogue, but note that they seldom help much with the switching spikes, what helps there more then anything is lossy ferrite beads.

I dont think tighter regulation (Within limits) has any real costs apart from possibly some small NRE cost due to design time and maybe a few more passives.

There are any number of companies out there that will wind you pretty much whatever you like, it gets much cheaper when ordering hundreds however.....

Regards, Dan.