On Sat, 08 Dec 2012 22:35:19 -0800, the renowned Jeff Liebermann
wrote:



Yes. The conspiracy theory is that components are selected to survive
no longer than the warranty period.

I think it's more a design spec than a conspiracy.

Looking at a typical specs of the internal parts of a linear wall
wart- at full rated current, the winding temperature rise is 70°C. At
a 30°C average ambient, if we assume the temperature in the wall wart
interior rises only 15°C (say half rated current), and 10°C internal
cap heating from the ripple current, we'll have the cap at 55°C. With
a 105°C/2000 hour rating, we should get

Life = 2000 hours * 2^((105-55)/K) where K is 10-15

Assuming K is 15, we get a life of 20,000 hours. Plugged in all the
time (24/7) that's about 2-1/3 years.

Run it at full rated current in a high ambient and you'll be at a
small fraction of that.

There are caps that will last longer, but they're too expensive to use
in an AC adapter.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
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