In my opinion, it seems inappropriate to rely on equipment, external to the
test subject, to determine emissions performance. i.e. the attenuating effect
of whatever your USB device is connected to, which will be highly variable
between various hosts. The test subject should be assessed in its own right.
In the absence of a conducted emissions test in the directly applicable
standards, I would be tempted to ‘borrow’ or apply an appropriate test from
another EMC standard.
e.g. Conducted Emissions DC Emissions from, say, EN 301 489-1. This uses the
method and limits from EN 55022 but using a DC power source. I would feel I’ve
done all I should to determine the USB device’s emissions.
Awaiting rafts of disagreement……
Tony
----- Original Message -----
From: Gartman, Richard
Sent: 05/05/11 07:32 PM
To: [email protected]
Subject: [PSES] Opinion regarding USB and EMC testing
Panel of experts ..
To demonstrate compliance with the EMC directive, products that have a
“path” to the AC grid must be tested for:
Radiated Emissions < 1GHz – EN 55022
Radiated Emissions > 1GHz - EN 55022:2006+A1:2007
Conducted Emissions – EN 55022
Radiated Immunity – IEC 61000-4-3
EFT – IEC 61000-4-4
Surge – IEC 61000-4-5
Conducted Immunity – IEC 61000-4-6
Voltage dips & Interruptions – IEC 61000-4-11
Harmonics – IEC 61000-3-2
Flicker – IEC 61000-3-3
ESD - Electrostatic Discharge – IEC 61000-4-2
A product with a UBS connector has a path to the AC grid. The 5V on the
connector may be provided by an AC adapter or a piece of ITE equipment, i.e. a
computer. If the “device” can ONLY be powered by a USB connector from a
computer, does the “computer isolation” on the path to the AC grid reduce the
testing required to demonstrate compliance of the device? The “device” would
only function when it is connected to a computer via the USB.
Configuration example:
Line voltage => AC adapter => Computer => USB connection => Device
The USB connection would also be providing data between the computer
and device
I would be interested in hearing any opinions on this.
Thank you for your views
W. Richard Gartman, MS, CSP
Product Stewardship Manager
Texas Instruments, Education Technology
7800 Banner Drive, Dallas, Tx 75251
Office: 972-917-1636 Email: [email protected]
<mailto:[email protected]>
www.education.ti.com/us/productstewardship
<http://education.ti.com/us/productstewardship>
Car racing also prepares you for and expects you to live in the moment
– perspective comes before and after the race. Preparation equals success.
<http://education.ti.com/us/productstewardship>
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