[RFI] buying a AC adapter

[Jim Brown]

On 4/26/2013 4:29 PM, Aaron Kreider wrote:
> Are class 2 adapters mostly or entirely linear? 

"Class 2" means ONLY that the thing connected to the power line is 
sufficiently insulated against electrical shock that it is alloed to be 
connected to the power line with a 2-wire plug (that is, no safety 
grounding pin). Both linear and switching power supplies CAN be built 
this way.

In general, nearly all linear supplies are clean and most switching 
power supplies are dirty.  There are exceptions to every rule.

Also in general, the heavier the "wall wart" sort of supply, the more 
likely it is to be a linear supply. Older supplies are also more likely 
to be linear.  Hamfests are a good place to find old linear power 
adapters, and they're usually cheap.  MOST, but not all, power adapters 
have little more than a step-down transformer and bridge rectifier. Some 
may also include filter capacitors. All of these provide DC, but 
capacitors are needed to filter the DC.  A few power adapters are ONLY 
transformers with no rectifiers or filters, and are designed for use 
with rectifier and filters in the equipment.

And if that isn't enough, there are at least a half dozen different 
types of power connectors, not including those on equipment like cell 
phones, tablets, etc.

  All this means that you need to carefully study what you're buying and 
make sure it's what you need.

73, Jim K9YC