Poor Line Regulation LNK420

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Hi PI Expert,


We have designed a LNK420 based 40 Watt LED driver to operate from 86 - 300 VAC.


But the line regulation is poor and the output current variation is 10%.


can you guide us to improve output current with in 5%?





There is a series resistor coming from the peak detector to Vpin and has a typical value of 4Meg. For wide range operation, a second resistor connected from V-pin to GND may be necessary in order to improve line regulation (see DER-384 for sample schematic and new values of pull-up and pull-down resistors).


You can try to increase the value of series resistor coming from the bias winding especially if there is high leakage on the transformer.


Please also check if it's required by the customer to have 5% regulation over line or is it acceptable to get 5% between nominal input lines (i.e., 115V and 230V). If you still require tight CC across entire line and the suggestions still can't meet it, then you need to consider adding extra feedback circuit to directly sense the output current (closed-loop feedback).

Hi PI-Crumb


Can you give link to download DER-384?