Hi Richard –
IMHO, considering the path to the “AC grid” is not the correct
thinking when identifying test requirements. Instead, within the EU the list
of tests are determined by function and intended use. As an cautionary tale, I
(and many on this list) have seen many portable products fail ESD testing when
on battery power *AND ALSO* when on their chargers. Connection to the “AC
grid” had no effect on the failure. That is just one of many tests that can
fail or pass independent of connection to the “AC grid”. I recommend caution
when trying to reason theoretically whether a test is important or not. Always
better to gather some data to support a line of reasoning.
But, maybe a more general question would be: “can test
requirements be reduced based on number and type of cable connections?”. The
answer is that in general, any test list can be reduced to as few tests as
desired. Sounds like good news, doesn’t it? A manufacturer is allowed to do
this as long as the reduction is supported with engineering data, discussion
and rationale rolled into a formal Technical File. However, a word of caution
on that path: deviating from a product standard breeds scrutiny and skepticism
from customers. It may be worth the extra cost of testing just to ensure
confidence from your customers.
As always- my opinion only.
Best Regards,
Patrick
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From: [email protected] [mailto:[email protected]] On Behalf Of Gartman, Richard
Sent: Thursday, May 05, 2011 12:32 PM
To: [email protected]
Subject: 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.
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