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Can someone please tell me how the values of RV, RV2, RFB1 on page 16 of the Design Example Report (Revision 2)and the values of RV1, RV2, RFB1, RFB2 on page 18 correspond to the circuit diagram on pages 7 and 8 and the Bill of material on pages 12 and 13? I'm just getting the feeling that the resistor values in the transformer design does not have any bearing on the actual circuit. Please HELP. To what circuit does these resistors refer to?

On the spreadsheet, RV is the same as RV1 described as upper Vpin resistor. RV2 is for lower Vpin resistor. RFB1 is upper FB resistor and RFB2 for lower FB resistor.

In the circuit diagram, however, the upper Vpin resistor corresponds to R2, R5, and R8. The FB pin resistor corresponds to R10. There are no RV2 and RFB2.

I think the confusion here is that RV1 and RV2 in the schematic are actually surge protection components, and are not related to the values in the spreadsheet.

Thanks a lot.
1. In the schematic RV1 is 3.887Mohm while in the bill of material it is 4.1Mohm. Why the difference?
2. In the transformer design spreadsheet there is a RV1(3.91Mohm) and a RV2(1.4Mohm). In the schematic there is no RV2. What is happening here?
3. In the transformer design RFB1 is 90kohm while in the schematic and the BOM R10 is 78.7kohm.
What is the correct values for 1. 2. and 3. above then?

Two important functions of Voltage monitor (V) pin are: a)It sets the line UV and line OV threshold; and b) Together with FB pin, it controls the output LED current.

In a usual wide-range input spec of 90VAC to 265VAC, Vpin resistor can either be: (RV1=4Meg, RV2=OPEN for dimming applications),(RV1=3.91Mohm, RV2=1.4Mohm for non-dimming applications. RV2 provides line compensation such that the current regulation over wide range input is better. In DER-286, however, there was an acceptable current regulation already even without RV2 and that is why RV2 was not installed (-response to q.2)

The spec for DER-286 is actually up to 308VAC. In this case, a value of 4.1Mohm as listed in the BOM is the correct value in order to avoid triggering the line OV threshold (107uA). Please choose Vpin resistor based on your operating conditions. (-response to q.1)

On q.3, RFB1 value was changed because unlike in the spreadsheet wherein the bias voltage is fixed (ideal), its actual value will vary depending on the transformer design, and it could be off by 1 or 2 volts, and therefore you need to adjust RFB1 accordingly in order to meet the desired current.

Now this is getting somwhere! Thank you.
We already have LED light units that used another type of PSU but the power factor is very poor and the inrush current is inhibitive. We urgently need 2600 new LED drivers. The DER 286 looks perfect for this application with the only difference being: we need an output voltage of 12.3V at a constant current of 1.75Amp and obviously as good a power factor as we can get (at least 0.9).
1. Looking at your response... should I start with the transformer design and these specs and then do some further imperical iterations to get to what we want or can someone of you people help me reducing the R&D time ti get to our specs?
2. This is quite an urgent matter and we don't have a lot of time to get the new LED driver to production.
3. I am strugling to get the local distributors to co-operate in getting the LNK419EG. Is there a possibility to deal with PI directly? We are in South Africa.

You can modify the transformer design to meet your specs. I provided a sample PI expert design using a smaller transformer since your power requirement is lower. Anyway, please feel free to modify the spreadsheet if you want to use other transformer.

Please double check that the power components such as output rectifier,output capacitors, etc, have correct voltage and current ratings.

With regards to the availability of LNK419EG on your region, please contact the nearest PI sales office in your region or you may directly contact PI sales here in the US:

5245 Hellyer Avenue
San Jose, CA 95138 USA
FAX: +1-408-414-9765

You can find more sales information at :

Thanks so long. I did contact our local distributors but for 3 weeks now they cannot come back to me with prices and deliver times. So I think I will just contact the USA sales office.

I don't see any gapping information in the transformer design. Can I safely accept that the transformer design do not use any gapping or will I have to verify this at prototype level looking at the transformer saturation?

Please ignore my previous message about the gap information. It is very clearly specified on the spread sheet.

Thanks for the support.