90W LED Driver with LNK420

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Dear sir, We plan to freeze the design of LED driver with LNK420. Please advise feasibility of such a design for continuous duty. The PI expert passed the design with a comment 'The device is small for continuous duty'  Please advise what can be done to use LNK420 safely for this application.



Can you pls attached the design file so we can understand the problem better 


Dear Sir, Thanks for your reply. We actually used PI expert suite for freezing the design of three Drivers.

1.36V/1.6Amp,  2. 36V/1.8Amp 3.36V/2.48Amp  Attached please see the work sheets. We customised the transformer with Ferroxcube PQ3630-3c90 Core. In all the cases the design were passed but not Optimized. All factors considered we felt it is the fit factor which was higher than 100%.Please confirm. The Optimized designs recommended by PI expert uses the ETD39 cores which are too large for the enclosure and we felt the choice was rather conservative.


Even with the PQ cores the Expert optimized the designs only as long as the OVP was not selected. With the OVP selected we could not get the design "optimized" no matter whatever combinations of Kp, Vor and efficiency were tried. Please clarify how the OVP impacts the optimization.


In the case of the 36V/2.48Amp driver the design was passed with the rider "The PI device is small for continuous duty"  Please suggest a suitable package for continuous duty. We can increase the ACmin input voltage also. We can use 0.33Mfd/630V cap in the place of 0.22Mfd/630V.We can size the Heatsink also appropriately.Please advise the best course of action and send the revised design files for our ref and use.Regards


Fit Factor. If its more than 100% you need to check the actual winding if it really doesn’t fit. If it doesn’t fit, then either you reduced the wire size or increase the transformer size.
“PI device may be too small for continuous output power”. LNK 420 can go ideally to 78W for a wide range design as stated on the datasheet. I saw on your spreadsheet that you push the IFB to 182uA. Ideally we want to center it at ~150uA for better CC regulation. To verify if your design works, you need to double check your CC at line and load and temperature variations on your design.
OVP is just an additional circuit and should have no effect on the optimization unless of course your optimizing for cost where it could remove the OVP circuit. OVP has no effect on the other parameters.
Thank you for using PI-products on a lot of your project. I may also suggest that you can also contact the local PI FAE on your area that can probably help you faster on most of your inquiries.