------------------------ From: Muriel Bittencourt de Liz <[email protected]> Subject: Conducted emissions on DC Date: Mon, 09 Nov 1998 18:02:29 -0200 To: Lista de EMC da IEEE <[email protected]>
> Hello Groupies, > > I have a DC-DC converter ( for example ) and i'd like to measure its > conducted interference. How do i do this using the LISN? > > If i'm doing wrong, please correct me. > > Muriel > -- > > ================================================== > > Muriel Bittencourt de Liz > INEP - Instituto de Eletronica de Potencia > Universidade Federal de Santa Catarina > Caixa Postal - 5119 > 88.040-970 - Florianopolis - SC - BRASIL > Phone: +55.48.331.9204 - Fax: +55.48.234.5422 > e-mail: [email protected] > Homepage: http://www.inep.ufsc.br > > ================================================== Muriel: INTERFERENCE is a subjective term, but you can measure the conducted EMISSIONS from a DC-DC converter. Also, you can use a LISN as part of the test equipment/setup. But, there are several common LISN designs (each with its unique source impedance). The first task is to define which LISN to use. OK, let's assume you are talking about a consumer product to be marketed in Europe. That means an LISN which conforms to the EN source impedance requirements. Next, which interfaces of your product must be tested? If we assume a simple DC-DC converter, we immediately hit a problem. The EN specification is concerned with emissions injected back into the public power mains, and the European standard power is 50Hz AC. Your DC-DC converter defines itself as being incapable of being connected directly to the AC mains. (If it could be connected to the mains, you would have to call it an AC/DC to DC converter, right?) As I see it, you require additional equipment (an AC-DC converter) to connect to the power mains. Your DC-DC converter must either be equipped with such circuitry, and then tested as a whole. OR, you must specify a third party AC-DC converter, obtain one, and test your product with that specific accessory. In my market area (US military), you would then either have to supply this accessory along with each sale of your product, or you would otherwise have to ensure that the exact third-party equipment was always used along with your equipment. This isn't very easy to guarantee, since you have no control of the third-party's product. If your product does require a DC input, then I would think that the conducted emission requirement is not applicable directly to your product since you do not connect directly to the power mains. Hmmm, do I see a loophole here? If you make a product that has inherent nasty conducted emissions, do you just leave it to the consumer to buy a "wall wart" AC-DC universal converter to power your equipment? The "wall-wart" manufacturer can't be responsible for every unknown equipment that it may power (or can it?), and your product doesn't connect to the power mains, so you're not responsible. So that leaves the consumer responsible since they have assumed the role of "system integrator?" Comments invited! Now of course, you could use the LISN method to make a relative measurement of the emissions that your product injects into the official impedance (using a DC power source). And, you could also measure the emissions that your product injects into the official impedance (using a resistive load) placed into your DC output lines. These measurements would be technically interesting, although not very useful since the official impedance would be unlikely to exist on any real-world loads. (And not legally required.) And don't forget to protect the spectrum analyzer RF input circuitry from destruction caused by counter EMF across the LISN inductor. Always use an attenuator on the LISN signal output, and don't turn the EUT On or Off with the coax connected to the attenuator. Regards, Ed -------------------------- Ed Price [email protected] Electromagnetic Compatibility Lab Cubic Defense Systems San Diego, CA. USA 619-505-2780 List-Post: [email protected] Date: 11/10/1998 Time: 08:21:29 -------------------------- --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
