[TenTec] On Switching Power Supplies

[geoffrey mendelson]

On 1/16/2014 5:10 PM, Bob McGraw - K4TAX wrote:
> A few weeks ago during a discussion of switching power supply and related noise, I made a comment that the charger for my laptop computer did cause noise.
>
> Subsequently I did find need to replace that charger with a new one.  In comparing the two, one makes noise and one does not make noise.  Now the interesting observations, both were made in China, both have the exact same rating, both have the exact same symbols for certification.
>

I know someone is going to be upset if I say this, but you have to 
understand the process of certification in terms of noise. The CE 
practices what is called self certification, where the vendor takes the 
item to an approved laboratory, gets a report of compliance, and submits 
that report with other documentation (photographs of the circuit board, 
etc) and if the levels in the report are below the limits, the 
application is approved and therefore certified to be compliant.

The FCC used to test items themselves, they no longer do, and their 
certification is achieved the same way.

Once an item is certified, there is no policing of the products. No one 
checks to make sure that production units comply, or that they contain 
the same circuitry as the test units.

It's also interesting to note in a related way the same thing with part 
90 certification. I know a radio that passed part 90 certification, 
which includes a requirement to prevent the end user from changing 
frequencies except by changing pre-programmed channels. The radio has 
had it's internals reused in several different products, which since 
they are electrically the same the FCC accepted them for part 90 based 
upon the original certificate. The problem is that the other models do 
allow frequency changes. Basically no one cares. :-(


Geoff.

-- 
Geoffrey S. Mendelson 4X1GM/N3OWJ
Jerusalem Israel.