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UC3854B: conducted emission reduction

SMPL
Intellectual 551 points
Part Number: UC3854B
Other Parts Discussed in Thread: UC2526

Respected sir,

we are doing the EMI/EMC test of our SMPS(1600W) . It is failing at high frequency (Greater than 20 MHz)  region during conducted emission test.

We are using PFC Controller UC3854BDW and we are also using UC2526 as voltage mode PWM controller for DC DC stage.

Kindly suggest solution for this.

Regards,

Akshat

  • 0
    TI__Genius 10665 points

    Hi Akshat,

    This is a very broad question, so it's not something I can directly answer.  In general, since 20MHz is well above the switching frequency of either controller, the noise is more likely coming from a fast edge on a power device. As one example, you should inspect the signals at the boost MOSFET to see if there are edges in this frequency range.  If this were the case, increasing the series gate resistor would slow the edge down. You could also use a snubber or perhaps a D-S cap if you have room in your efficiency specs.

    If this isn't the case, probe around the board looking for fast edges and review the filtering you're using, especially at the input(s) and output(s).

    Also, board layout plays a big role and there are many ways that EMI can be affected by component placement, shielding, routing, etc. As you know, this is a big subject with a very wide scope, so it's something you'll have to look at if you can't resolve this with component changes.

    I hope this helped.

    Ray