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UCC28630: Peak noise at 700-750kHz

Franz Schellhase
Expert 3605 points
Part Number: UCC28630

Hi guys,

my customer uses UCC28630 in a 50W LED power supply. When measuring grid-bound noise (150kHz-30MHz) they notice some peak noise at 700-750kHz, which they were only able to filter out using a RC-Snubber (Drain MOSFET -> GND-AUX). Choke, suppresion capacitor and switching frequency of the MOSFET help everywhere else but not at the mentioned frequency range.

In previously designed lower power supplies they are seeing the same tendencies.

Is this a known phenomenon and can it be mitigated in different way?

They would like to save the reduction of efficiency caused by RC-Snubbers or prefer to move it to the transformer.

Thank you for your support,

Franz

  • 0
    TI__Expert 8210 points

    Franz

    Dealing with electrical noise that is generated from the harmonics of the switching frequency is a common challenge in switched mode power supply design.  For high voltage input designs, which UCC28630 targets, this noise can be even worse sine the ringing voltages are much larger.

    The way that this noise is commonly resolved is to use a snubber to dampen the ringing at the switch node.  For the UCC28630 EVM UCC28630EVM-572 these components are D6, C8, R12, D9, D8 and C16.  The following app note explains different ways to implement this snubber http://www.ti.com/lit/an/snva744/snva744.pdf

    If the snubber is not sufficient, either since the ringing is too large or the losses associated with it are too great, adding low pass RC filter around key pin of the controller and other sensitive pins can help filter out the noise from interfering with proper operation.  Proper layout, as all of our datasheets have in the end of the datasheet (section 11 page 74-75 for UCC28630) will also reduce the impact of this noise since it will reduce parasitic inductance and capacitance.

    Best Regards,

    Eric