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UCC28710: UCC2871//Audible noise

Part Number: UCC28710

Hi Team,

We have selected UCC28710 part no for 1 Phase or 3 Phase Power supply with 24V/3 A output, so in proto type we are facing audible noise as per low descriptions , when we have turn on at load so audible  noise observed 

please help to  troubleshooting 

Design parameters 

Output:- 24V/3A

NP-38,Ns-10 turns ,Lp-505uH

  • Hi Chandan,

    Thank you for the query on UCC28710.

    We recommend that you verify the max frequency of your design is sufficiently high enough to prevent the switching frequency from entering audible band (<20kHz) when significant power is being delivered. If your switching frequency is below 20kHz when it's audible we recommend you modify the design to increase the switching frequency.  You can use our excel calculator and simulation models available on our website here https://www.ti.com/product/UCC28710#design-development##design-tools-simulation  Feel free to share a filled copy of the calacultor and schematic to see if there are any discrepancies in components, esp. current sense resistor and magnetizing inductance.

    I would recommend reviewing the design to see which component is causing the ringing.  If it is the transformer, you can reduce or potentially eliminate noise by varnishing the transformer.  If it is capacitor (snubber) you can glue them to the PCB to prevent them from causing noise or use a metal film cap instead of ceramic.

    Regards,

    Harish

  • Please provide your inputs to the above to proceed further. 

  • HI Harish,

    thanks for the suggestion, now noise issues resolved but now we are not getting switching frequency which is consider during design time ,design time taken 100khz but now observed 30-33Khz only please advice further 

  • Hi Chandan,

    Seems from the limited pspecifications which you have shared, the primary inductance value of 505uH seems to be on the higher side. Using equations 14 and 15 of the datasheet you can calculate the magnetizing inductance for 100khz for Nps=3.8. Rcs comes close to 0.2ohm and Lm comes to 108uH. So you might have to lower the primary inductance to increase switching frequency.

    Thank you

    Regards,

    Harish

  • Hi Harish ,

    As per your last suggestion we have to calculate below parameter 

    Lm=120uH

    Turn ratio =4.5

    Np-32 

    Fsw=100Khz

    now noise issues resolved but Fsw is not meeting as per taken during design time so how can meet the switching frequency . 

  • Hi Chandan, 

    In your first post you had mentioned Lm as 505uH and a different turns ratio Nps = 3.8. Hence I suggested reducing this to push Fsw higher.

    Can you please confirm your design parameters? 120uH or 505uH being used currently? Can you please forward your schematic with component values so that we can support better?