Can I use larger, one level higher variant of PI device without changing the design?
I have designed a AC-DC power supply using TOP257YN with PI Expert 10. Now the device TOP257YN is not available however TOP258YN is available and we have a stock as well. Can I use TOP258YN without modifying the design or with a minor modifications to the design? The design is attached herewith for a reference.
With Best Regards,
John
Files
Attachment | 大小 |
---|---|
TOP257YN Design.PNG | 42.7 KB |
评论
Many thanks for the prompt reply. I shall try and revert back to you in case of difficulty.
With Best Regards,
John.
I went thru PIXLS to determine the necessary resistor value and got the value of 8.03 k Ohms. With some more tweaks on the PI Expert design, by updating the VOR, KP and CIN I could manage the design using the higher device for lower current limits. The design file (uds) is attached for your comments and approval. Instead of "Design Passed (Optimization Done)" it now says "Design Passed (No Optimization)". I have never seen any reliability issues when I use the PI Expert original design without any modifications when it says "Design Passed (Optimization Done)". Will this modified design work without any difficulty as the originally designed by the PI Expert?
With Best Regards,
John
Attachment | 大小 |
---|---|
TOP258YN with forced external current limit | 1.25 MB |
I opened the design, and didn't see any error or warning flags. AS an extra caution you might want to check that the transformer parameters in the new design are identical to those you used in the old.
Thank you. When you say I should check that the transformer parameters in the new design are identical to those you used in the old, do you mean all parameters including the core material, geometry, number of turns, number of layers? Can you please specify which parameters to be checked essentially?
Also I wanted to check with you in general, if I design a power supply using PI Expert by tweaking a few parameters and the design is ready with "Design Passed (No Optimization)" do I consider that it would work without any difficulty? So far I have only used the designs "Design Passed (Optimization Done)" which worked absolutely reliably.
With Best Regards,
John
The two things that you should care most about in this new design with a larger TOPSwitch is to make sure that the primary peak current is dialed down sufficiently by the X-pin resistor such that your transformer is not in danger of saturation. This is assuming that you intend to use the exact same transformer as in your previous design. With this in mind, you want to make sure that the transformer in the new spreadsheet has the same number of primary, secondary, and bias turns as your previous design, as well as the same nominal primary inductance, so that the spreadsheet does a valid check of your previous transformer working with the new TOPSwitch. You should get some low-line efficiency benefit by using a larger TOPSwitch with a dialed-down current limit (lower RDSon in the same design with the same output power). By the same token, high line light/no load performance could be slightly inferior to the original design due to the higher capacitance of the larger TOPSwitch
If you have no warning messages in your current PI Expert design, you should be good to go.
Many thanks for the clear guidelines and the answer. Closing the topic from my side.
With Best Regards,
John.
At the very least, you would need to change the value of the X pin resistor to reduce the current limit of the larger device to avoid possible transformer saturation. It would be a good idea to run the design in PIXLS to determine the necessary resistor value. You will need to specify parameters in the spreadsheet to force a design that would use the same transformer as your current design.