DER136 Modification

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with reference with DER136 ,we  have modified the existing design  with TOP244PN for 7W for 42V and 160mA , the problem we are facing is that we are not able to set the output cuurent to exactly or close to 160mA, by fine tuning the sense resistor the output current is either too low  or high, please suggest the changes that we can tweak at the output side , so that precision  current setting is possible , please note that the output transistor circuit we taken it as same , but the only change we made is with current sense resistor, 

please help me in this regards,

Please use either our LinkSwitch-PL or LinkSwitch-PH products for your LED lighting designs.  If you look on our design example pages (, we have a large number of reference designs that meet your design criteria.  In fact, there are a number of completed designs that could probably be leveraged almost completely for your use.


-The Traveler

We have a number of RDK/DER's with fairly low THD (many in the low teens) and the vast majority of them meet Class C harmonic requirements as does DER136.  


Can you give me an idea of what your power supply specs and requirements are?  Maybe I can help you locate an RDK/DER that might be closer to your application.  DER136 does provide good constant-current performance but as is the case with your experience, the feedback circuitry can be tricky to troubleshoot.



-The Traveler

With the non-isolated topology and low %A-THD requirements, I would really recommend going with our LinkSwitch-PL product line.  We have several RDK and DER designs with very low THD.


Here are some good starting points:


Your application's input voltage will affect your THD performance greatly.  I'm not sure if you're in a low-line, high-line or universal input category but if you can limit your design to one input voltage case it will really help with your design.  


Another nice aspect of LinkPL is that with the non-isolated topology, the IC can sample the output of the LED driver directly and not rely on a bias/feedback winding, an opto, etc.  This will improve the tolerances on your perforamance envelope, allwo you to create a less expensive design and will also make your design process easier as the feedback circuitry becomes *much* simpler.


Even if you do decide to use a TopSwitch solution, it would be best if you moved this post to the LED forum.  This will give you access to the engineers in the LED product group and they will be able to address any questions you have in much better detail.



-The Traveler