DPA423 - Device turn on transient/ fast edge EMC issues

Posted by: shoubhikdoss on 05/24/2013

Hello -

We are using the DPA423GN in a multi output configuration using a EF20 style transformer. The DPA switch works fine in every aspect except for emissions, both conducted and radiated.

The problem frequencies being 15MHz - 30MHz for the conducted, and

65MHz - 225MHz for radiated.

We have identified the ringing in the turn on transient of the internal device to be the source of these EMC issues.

Image 001 - shows the ringing post turn on

Image 003 - shows the high dv/dt during the transient

As the switch is internal there is not much that can be done in terms of slowing it down by gate resistors.

Please advise if:

1. The transformer windings could be altered to minimize this unintentional current flow through from the primary to the secondary. We do not have any shield winding in it right now.

2. Any active/passive network between the drain-source terminals to alleviate the problem.

Files

003.png (55.53 KB)

Comments

Could you upload schematic and layout?

thanks

Please find attached the schematic and layout of the DPA423 attached. These are screen captures in a word file. Thanks.

Shoubhik

I found that Zenner was used for the snubber at primary side. Would you like to try RCD snubber? PLS make sure that the RCD snubber has good damping.

regards

I can surely try that; however, would a RCD snubber also help supress the ringing in the tunr-on transient as shown in the screen captures? Thanks.

PLS use RC snubber for the two output diodes at secondary too, and I believe they can reduce the ring by them. Y cap between primary side to secondary can help you to solve the issue too.

Sorry to response you late.

I will give this a shot.. Thanks for responding.

Regards,

Shoubhik

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