I wonder if anyone can help me with my confusion over the proper way to evaluate conducted EMC on the DC input lines to DC-DC converters.
Our radios are available with a variety of slide-in modular supplies, including 24 and 48 VDC. When DC power is ordered, it is up to the customer to have a source, we don't provide a line operated DC supply. When EMC labs have measured line conducted on the DC radios, they have used either a "golden" or customer specified AC-DC converter (i.e., DC power supply) and placed the LISN between the AC side of that supply and the mains. Any conducted noise produced by the supply itself is "subtracted out" supposedly leaving any noise put out by the radio and its DC-DC converter. We are now looking at some DC-DC converters for their conducted noise levels. The power supply manufacturer is measuring noise by using a standard 50 uH LISN on the DC input line (as opposed to the AC supply line). Is this generally considered an acceptable method of measurement? On the one hand, you are looking at the noise where it first appears, but on the other hand, regulatory concern is for noise getting back into the mains. Also, are the 50 uH chokes in commercial LISNs typically air core so that they can carry DC without saturation ? Our ultimate requirements are to meet FCC Part 15 and EN 55022. What are the gorup's opinions ? Thanks, Jack Jacob Z. Schanker, P.E. Director of Agency Compliance California Microwave 716 242 8454 (voice) 716 242 8427 (fax) [email protected] --------------------------------------->
