DER-845 - Irradiated emissions

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Hi, we developed a circuit based on the DER-845, but we're facing some irradiated emissions problem for class B category and a high pitched audible noise (around 6 kHz to 7 kHz).
As a company policy, I'm not able to share the schematics / layout here in the forum. How can I send my files so you guys can verify what we can do to make it a better design ?
Best regards, Drauzio.


Radiated emissions from this topology usually come from the loop consisting of the input capacitor, the freewheeling diode, and LNK3296. This loop acts as an antenna and minimizing its area is imperative. Looking at DER-845, below methods should help:
1.) Placing C2, C7, D5 and U1/U2 as close possible to reduce trace lengths.
2.) If necessary, place a 1kV high frequency ceramic bypass capacitor directly across U1/U2 drain and D5 anode. Values between 100pF to 1nF should suffice.
3.) If still necessary, an RC snubber circuit across U1/U2 drain-source should also help. Values are up to 100pF for the capacitor and 10 to 100 ohms for the resistor.

As for the audible noise, 'glueing' L2 (buck choke) to the PCB to minimize vibrations is also helpful. We also had some success with increasing C4 (sample-and-hold capacitor) from 10uF to 22uF/33uF but at a cost of adding a few mV to the output ripple voltage.

Hope this helps.


Hi PI-BERJ, thanks a lot for the information. We will try it here, and about the pictures and schematic that we have, is there any email we could send it so you guys can check more stuff for us ?
Thanks again.
Best Regards, Drauzio.

As a company policy, we are also not permitted to post our e-mail address in a public forum. However you can give us an e-mail address and we can exchange information privately.

PI-BERJ, here's my email:
Best regards, Drauzio.