FEDEVEL
Platform forum

Sniper2 , 04-25-2024, 04:21 PM

What is your target for EMC precompliance ?
How bad is 45dBuV?
And 51 on a smps mosfet?
PS i am considering all standards EU and US also the stricter ones
PSS measurements were with near fiel probe on the PCB so no metal enclosure and earth GND

QDrives , 04-26-2024, 03:42 PM

45dBuV at what frequency?
As you mention near field probe, I assume you mean radiated?
Near field is no indication on far field. It helps finding the source.
You also did not mention which near field probe (ie. size).
For example CISPR 11, class B - 30...230MHz = 30dBuV @10m and quasi peak.
https://www.academyofemc.com/emc-standards

Sniper2 , 04-26-2024, 04:18 PM

100KHz -500k if i remeber well

Sniper2 , 04-26-2024, 04:18 PM

yes

QDrives , 04-26-2024, 04:37 PM

"Yes" to what?

150kHz to 30MHz is in conducted range. 30MHz and higher is radiated.
For conducted you measure the currents on the cables (microamps!)
You use a LISN to measure the conducted emission.
Watch videos of Min Zhang (Mach One), like this one https://www.youtube.com/watch?v=0uCXs602_6M

QDrives , 04-26-2024, 04:38 PM

Below 150kHz are few standards and the emission limits are something like > 50dBuV.

Sniper2 , 04-26-2024, 07:51 PM

yes as in radiated

Sniper2 , 04-26-2024, 07:52 PM

THX

QDrives , 04-27-2024, 03:27 PM

"yes as in radiated", but the frequency "100KHz -500k if i remeber well" is in the conducted region.
Do note that spikes at 100kHz can (will) have harmonics in much higher frequencies.
I have seen problems with the 19th harmonic of an 8MHz oscillator.

Sniper2 , 04-27-2024, 03:32 PM

well i set the max bandwidth when probeing

Sniper2 , 04-27-2024, 03:32 PM

i didnt read the required specs and i was only told that 50dbuv was on the high side

QDrives , 04-28-2024, 06:30 PM

As with everything in electronics - "it depends!".
At 100kHz measured through a LISN, you will probably be ok.
At 50MHz radiated measurement at 10m to CISPR 11 class B, you are over 20dBuV above the limit.

Another question is: can you think of something cheap and simple to improve it, regardless of the standards/limits?

Sniper2 , 04-28-2024, 06:50 PM

decoupling caps and series resitances

Sniper2 , 04-28-2024, 06:50 PM

optimised like 10-12bbuv from that alone