PFS726 output power is limited to 200W!

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when performing various test with PFS726 we noticed, that is working very well

until 200W of output loat, but when load was increased to about 250W the output

voltages goes low as 310V from initial 385V. Till 200W the power factor is very high

what we can see from input currerent waveform. 

The question is what could be a reason, since we use the same circuits like for 900W version

with PFS729 from data sheet?


Which components could have such effect? We also tryed to cool down PFS726 with

external ventilator if for some reason some temperature trip accured. 


thanks and best regards. 


It can go into power limit if the PFC inductor value is too small.

Could you please let me know what is the input voltage of the converter when this problem occurs.

Could you please send me the schematics, PIxls file and PCB Layout files for review.





we did't use PIXls designer, because family of PFS72x is not supported like I can see. We took

schematics from data sheet, where PFS729 (900W) is showed. Regarding PFC inductor we use

IRON core T157-60 (micrometals) which has 1.8mH at 2.5A and 1.2mH at 6A. We tryed various input

voltages from 160V DC .. 315V DC, which was measured after diode bridge.





PFS72X device family is supported by PIXls designer.


Please find the attached PIxls file with PFS726.


Please send me the schematic, and probably capture the inductor current waveform at this condition. We will the review the schematic and suggest you if it requires any changes.


Since powdered Iron has higher core loss, compared to ferrite and sendust material, I wonder as if the core is getting saturated in your case becuase of thermal runaway.


you can try using sendust core or ferrite core if the inductopr is getting saturated with powdered Iron core.






thank you for design. I have checked it and I can see, that there are some component difference between

PIXls design and our schematics.

I will try to capture inductor current, but in a mean time please check attached schematics, for possible

mistakes, which could lead to power limitations.


thanks and best regards




Please implement following chnages in addition to the inductor change.


1.Remove R67.

2.Change D8 to 1N5408-T (because 1N4007 will not be handle peak inrush current)

3.Add a 470pf capacitor from R73 to GND.


I am not sure about how you are getting the Vcc supply for the IC. If it is regulated 12V the circuit is fine, If it is not regulted please use the circuit which is shown in DER-274.