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25w non dimmable driver

Posted by: stalindm on Wed, 07/04/2012


    we made a 36v, 0.7A non dimmable led driver using LNK409.We followed der286 as reference and we got current 500ma to 630ma for an input variation 90v - 245v. Please find the attached ckt diagram and spread sheet design.

Observation is as shown below for input variation 90 - 245v.

IFB - 140uA - 150uA

IV  -   33uA  -  84uA

VB - 20.3V  -  21.6V

Out put current is less than expected and there is no regulation. Please let us know what is wrong with our circuit.




Attachment Size
DER286.pdf 17.55 KB
25w non dimmable.xls 43 KB


Submitted by PI-Dunwell on Wed, 07/04/2012

Youre almost there. Rv value on the spreadsheet is 3.9 M, yours is 4M (R2 + R5 +R8). The spreadsheet also calls for Rv2 which is 1.4M. Rv2 is the resistor connected between V pin and source pin (not on your schematic). You need this resistor to improve your regulation.

Submitted by stalindm on Thu, 07/05/2012

Thanks for your advice. We changed Rv to 3.9M and added 1.4M as Rv2. But we are not getting any regulation in output current. When we changed the feedback resistor to 78k( that means IFB more than 220uA) we get 480mA out put current with good regulation. Transformer winding is very tight and as per PI expert software construction instructions. Is it the problem with EI28 core? Also we put a flexible band outer covering with copper foil as per der286. Please help us to solve the problem.



Submitted by PI-Dunwell on Thu, 07/05/2012

I'm not really sure what else is causing you problem. Pls check your layout if R12, C9 and the Rv2 resistor is closer to the source pin , it might be noise. Have you tried using a 419 device?