Universal Power Adapters: How Do They Work?
Universal power adapters are unlike the power adapter that ships with your notebook. The most obvious difference is that the aftermarket adapters include a variety of tips. Each tip has a unique fitting to accommodate as many manufacturers' hardware as possible. Vendors use a range of voltages, and varied sizes help prevent connectivity between incompatible components.
Even within a single brand you'll find notebooks that use different voltages and plug sizes. For example, Dell has a standard plug size, but the Inspiron Minis don't follow it.
Here's another difference: the stock power adapter that ships with your notebook supplies voltage at a fixed setting. This is not the case with universal power adapters. In order to satisfy the multiple voltages required of different devices, they must be capable of outputting different voltages as well.
The switching mechanism is in the tips. Inside any given tip, there is a sense resistor that has variable resistance to the current supplied by the power adapter. This resistor drops the voltage as the current crosses its path. The small voltage drops are then fed to a simple comparator circuit, which then is used to further control the DC output from the power supply.
|Tip # (Targus)||Voltage||Pin 1-3 resistance (kΩ)||Pin 1-4 resistance (kΩ)||Connector ID (mm)||Connector OD (mm)||Connector length (mm)||Systems|
|L105||16.5||13.9||168||2.5||5.5||11.1||IBM (older T4X connector)|
If you take measurements from the tips themselves, you'll notice the difference in resistance output. Pins 1 and 2 supply power to the computer, and we've numbered the pins from the center pin in the connector. Pin 1 is negative and pin 2 is positive. These measurements are unique to the tips, not the adapter.
With the technical explanation out of the way, let's compare three universal power adapters.
That seems unusual. In my house we have 3 different laptops spanning 6 year purchase dates and they all have the exact same plug. Two of the laptops are Latitudes and the other is a Studio XPS. The only difference is that the Studio XPS came with a 130 watt adapter as opposed to 65 watt adapters for the Latitudes. So no gaming with that machine while plugged into the 65 watt adapters.
Actually this sort of standard DOES exist in Europe for smart phones and cell phones, I'm not sure if it includes laptop or netbooks but it might. I'll have to search around.
It seems the bottom line today is buy the OEM adapters if you want to play it safe.
come on Toms, get the BD benchies out already.
So that $800 laptop then requires another $270 to run after 3 years? And this is assuming you don't drop the thing, or break it through normal wear and tear. And laptops do not age as gracefully as desktops because they are generally crap hardware to begin with. Much better to stick with a $300 laptop, and a decent desktop. The desktop will keep up with the times longer and will have less maintenance, while the laptop can be swapped out when need be.
Instead of buying a new Lithium-Ion batt (that would only last about another 2 years anyway), I just use a 12V 7.2Ah Lead Acid connected to the PSU input when I don't have access to a mains supply for an extended period (e.g. on long train journey).
It works cos the PSU output voltage is 15V so 12V is close enough.