Problems with LED Driver 115W

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Iam having a problems in the output driver. Without load, the output voltage is 90 VDC. With charging drops to 60 VDC. With this, I cant reach the desired current on LED and I dont know if it is some error in the project with the diodes VR1 or the diode D3 that I defined. Wait your comments and helps. Thank you


Best Regards,


Murilo Dyple

Murilo -


Can you please attach a PDF of your circuit schematic, PCB layout as well as your transformer build diagram? 


-The Traveler

Attached files!!


I still have the same problem..

Murilo -


Sorry for the late reply.  I had responded a few days ago but for some reason my response didn't get posted to the forum :-(


I was hoping to get the actual schematic and PCB layout that you're using in your design but assuming it's very similar to the PI Expert schematic I have a few suggestions.


Primary side regulation:  At your power levels, primary side regulation is not going to work well.  With the poor coupling in your transformer, primary side regulation will be even more difficult.


Constant Voltage vs. Constant Current:  The feedback method you're using would implement a constant voltage type feedback scheme.  With an LED driver, you need to sense and regulate the output current because LED forward current is exponentially proportional to the LED forward voltage.  Small changes in Vf will create HUGE changes in If.  


Transformer Design:   

This transformer has some serios design issues.  The number of layers being used for both the primary and secondary are excessive and will cause problems with proximity and skin effect related losses.  Also, the winding arrangement will create poor coupling from primary to secondary.  The poor coupling will create high leakage inductance, increasing your clamp losses, dropping efficiency and further increasing your regulation problems in primary side feedback designs.


To implement an accurate constant current control scheme, you'll need monitor and regulate the output current directly (especially at the power levels you're working with.  Something like this IC would likely do the trick for you


I hope this is helpful.  Please let me know if you need any further help. 






-The Traveler