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UCC28710: Audible Noise from the UCC28710 controller based Flyback power supply

Part Number: UCC28710
Other Parts Discussed in Thread: UCC28704

Hi Team,

We are using UCC28710 controller in the fly-back power supply .The input range is of 110V to 230V single/three phase and the output power requirement is of 60W. We are facing an audible noise from the transformer when the DUT(Device under test) is powered on with load >0.5A and the noise is gradually increasing w.r.t  increase in load .Kindly let us know how to troubleshoot and suppress the audible noise.

  • Vishal

    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 

    If you cannot change the design, we 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 you can glue them to the PCB to prevent them from causing noise.

    Best Regards,

    Eric

  • Hi Eric,

    Thank you for the reply. Attached the design that we are using except the controller is UCC28710 instead of UCC28704. The transformer used is already varnished and we have tried replacing the ceramic capacitor C2 in snubber circuit with Metal film capacitor but there is no improvement in the audible noise. Can you please let us know how we can prevent the switching frequency from entering audible band (<20kHz).We are not sure which component is actually causing this issue.Kindly suggest any work around that can be used to troubleshoot and eliminate the noise .(The work around should not impact the design requirements)

    1106.2273.Flyback_convertor_A0.pdf

  • Hi Eric,

    Can you please update on this?

  • Vishal

    The switching frequency is determined by the inductance of the transformer.  The schematic you provided does not specify what the inductance of the transformer in your design is.

    Equation 16 (page 20) of the datasheet shows how to calculate the inductance of the transformer.  In this equation "fmax" refers to the maximum switching frequency of the design, which for UCC28710 can be up to 100 kHz.  You can use the excel design calculator for UCC28710 https://www.ti.com/lit/zip/sluc590 to make this calculation, as well as verify parameter values for the rest of the design.

    What we recommend is that you set the switching frequency is as high as possible.  This will help reduce the instances where the switching frequency is below 20kHz, reducing the generated audible noise.  At this point if there is still audible noise, mitigation techniques such as varnishing the transformer typically enable designs to no longer have audible noise concerns.

    Best Regards,

    Eric