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PMP11303: PMP11303

Part Number: PMP11303


I want make a similar desing PMP11303 for a 55V output and 6A. I made the design, but if i don´t have output load the voltage is over the 55V (90V) for this reason i want knowing if it's necesarie a outputload for a correct output in PMP11303 desing or it's possible that my desing it´s incorrect. (The schematic it's similar but with other values)


  • Hi,

    For a half bridge LLC, the turns ratio should equal to Vin/2Vout at resonant frequency. If your did design your turns ratio for 55Vout, then the other possibility causing output voltage going so high is the parasitic capacitance on both output windings and output rectifier. Usually you can observe the over-voltage condition at light/no load condition in high output voltage designs. To verify it's a power stage design problem or the parasitic capacitance problem, you can simply apply 30%~50% load to the output. If with 30%~50% load the output voltage drop back to ~55V when switching frequency at resonant frequency, then it is parasitic capacitance problem. You will need to improve your transformer design and/or add some dummy load to help lower output voltage at light load.

    Sheng-Yang Yu