Why do laptop power adaptors need earthing. Output is 2 wire DC ..?

Question

The earlier models were 2 wire input, but present one's are 3 wire.
Input voltage typically is 100 to 250 volts AC, autosensing

Why this change in design ?

mike > just tested continuity: outer sheath or -ve to ground terminal on plug >> nil > no continuity

Requirements of the ....

Mike,
first half of your answer seems more apt
i frankly do not see any safety or technical issues
some weird regulations or something at work, is how i see it for now !

Billtronix,
simple snubber's do the job for most elementary circuits. a laptop adaptor is lil more complex than a desktop smps unit. no voltage selector switch for 110 / 220 volts, no cooling fan & ventilation > fully enclosed & sealed unit

Thanks rhsaunders,
technically > i. case is hard plastic / often abs too, hence leakage to case almost ruled out ii. very basic solid state relays employ optic isolation., hence leakage of line voltage to dc supply can easily be eliminated at low cost & space
am actally not sure if optic isolation is presently being used or not
here again, second part of your answer sounds more appealing, lol

Thanks Philip,
the advent of the m or mobile processor is revolutionary indeed and is still evolving furthermore, good., but as u mentioned > higher sensitivity, which fact is not good ... however does not matter
plenty many advances in power & control electronics too
repeating from above, a snubber on line side absorbs most of the spike, besides protecting primary ckt. & optic isolation ensures non of the residual ripple is passed onto dc output or secondary side

wanted to share another interesting comment i came across > 2 pin wall sockets are becoming increasingly rare !

Answer 1

I could go on forever with a variety of valid reasons for this, however, the true determining factor has mostly to do with the new series of processors (low voltage -dual core) used in modern laptops.

Given their higher sensitivity to electrical current it became imperative that manufacturers take every precaution necessary to safeguard them from as many possible risks of even the slightest "spike".

That's it .... that's all.

Yes .... we could say that it is a safety precaution in regards to external factors such as environmental wiring or such, however, given the sudden low power consumption of processors & subsequently laptop PCs it is clear that the power input must now offer a substantially lower ratio (range) of potentail fluctuaion than on earlier units.

I remain supremely confident in this conclusion & believe firmly that all other explainations are mere speculation.

regards,
Philip T

Answer 2

As usual, the safety ground is intended to protect users of the appliance from possible leakage voltage that could appear on the case due to a fault in the device's electrical system. A failure in the adapter could allow line voltage to be superposed on the DC supply to the laptop, posing a hazard. It is not a particularly significant hazard, as few exposed parts of a typical laptop are metallic, but there is a growing tendency toward emphasis on safety.

A funny tale is relevant. I had brought into my office a fluorescent lamp fixture, of the kind that is often used under kitchen counters. The company safety people gave me a hard time about it, as it had only a two-wire cord. I told them that I would be happy to put a three-wire cord on it, if they would tell me where to connect the ground wire; since the thing was entirely made out of plastic, there were no metal parts to ground. They decided to let it be.

Answer 3

Requirements of the insurance and testing industries having to do with when you are allowed/required to use non-polarized, polarized, and ground plugs. The most likely answer is that the outer sleeve of the DC is connected to AC earth ground and if it plugged in reversed, it might be at 120 AC above earth ground, like the toaster I once owned.

Answer 4

It is just a step to protect your equipment. the ground takes any excess voltage or surges and doesn't let it spike your computer. It leads to better battery life and less electronic damage. Not that there was much before, it is just safer. Good luck.