der286 o/p current

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we made a 30w led driver using der286 . We followed every thing as per

der286 except the flyback transformer  and link switch. Link switch we

used lnk409 instead of  lnk419 and transformer  we used EI 28 as per PI

expert spreadsheet design. Also please note that we didn’t use OVP

We get output current 600-750ma for an input variation of 90to 245v.

Output current is increasing as input increases. We changed the

feedback resistor value to 98k then current starts regulate at 660-

700ma range for input variation 100-240v. During this regulation Ifb

varies from 190uA to 230uA. Also bias voltage varies from 23.8 – 24.8v

for an input variation 100-245v.
Please tell me what is wrong with my circuit.



I'm assuming you have a spreadsheet for your design. Make sure expected output current on the spreadesheet matches with yout Iout specs and there are no warnings. 


Make sure that the bias voltage you enter on the spreadsheet is the same as the bias voltage you were measuring on your board so that your IFB values are consistent. 


Please make sure that Iv and IFB currents on your spreadsheet matches with whats on the board.You cannot go above 220uA IFB, spreadsheet will issue a warning if you do that, and device will skip cycles.


There is also a trimming portion at the bottom of the spreadsheet where you can adjust the Rv resistors and RFB resistor to trim the output current.