Conducted noise doubt
I'm reposting a previous doubt since i think i ve got some more information of the situation now.. :)
I'm working on a PLC communication equipment.An AC/DC converter specifically a fly back topology converts the input power to DC voltage for the rest of the circuitry operation in the unit.
The P & N wires that are coming to the AC/DC converter are themselves used to transmit signals to and receive signals from, the PLC channels in the band 2-100MHz.
The AC/DC converter should not couple any noise to the Power line channel since it will affect the SNR of the signal.
The typical requirement is like that the noise levels should be equal to -150dBm/Hz (PSD) in the channel over 2-100Hz band.The background noise in PLC channels are measured in PSD and any injected noise power from AC/DC converter can affect the SNR.
A detailed measurement procedure of PLC channel noise levels can be seen at the link
(http://www.ict-omega.eu/83B4379B-A7F...Omega_D3.2.pdf) page number 92.
So i think the best solution will be to provide an filter stage in the AC/DC input (prior to the place of coupling of transmit signals) to kill conducted & common mode noise arising from the flyback converter to the PLC channel.
1. So is it possible to design such a filter , does standard power line filters are available or do we need to custom design the same..?and what will be the best method to follow, since i ve not completed design of the converter i cant know its noise levels.. ?
2. Also is it possible to convert the PSD levels into dBuV conucted emission measurement units with a similar test setup specified as in the document?
Thanks for any help,
ku637,
Your design almost requires a 'diplexer' connected to the AC line with outputs to (1) the PS and to (2) the PLC communications equipment.
Most common AC Line filters employ a 'Pi' filter with shunt caps to ground either side of an inductor. This would shunt PLC Comms to ground.
This design almost certainly calls for a custom design; I hope you are familiar with filter design ... at the outset you might be able to employ a standard AC Line filter before your flyback PS, but you will required additional LC circuitry in front of the AC Line filter to 'isolate' it from frequencies your PLC communications apparatus uses.
So, from the AC Line input then following rough filter topology would exist:
AC Line ------ High Pass Filt above say 1 MHz (first series element = Capacitor) -- PLC Comms
. . . . . . |
. . . . . . |----Low pass Filt below say 100 kHz (1st series element = Inductor) --- AC Line Filter --- PS
Values of course TBD.
As for PS noise, is it possible to use values supplied for a similar design by a manufacturer of SMPS as a starting point?
Regards,
RF_Jim