how do mobile devices such as laptops, phones and etc, ground themselves?

[glsn]

a quite dumb question came into my mind...

 

[ThrashZone]

Hi,
Negative battery only needs a little metal to be a ground.

 

[glsn]

Hi,
Negative battery only needs a little metal to be a ground.

more info about it?

googling online I either foundout that they don't really need a ground because they do use the negative end of a battery (?), and that the case should be double insulated, even though that doesn't always happen

though from a quick look to any laptop inside, it looks like they do use like a sheet of metal that should also be used as reinforcement structure and em shielding;
though if that sheet is used as a ground, what happens if the case is fully metal? or they don't and use anyway composite materials?

 

[ArdWar]

They use one supply polarity (typically "negative" one) as a ground reference and that's it. They don't have literal ground connection. "Double insulation" is safety and regulatory requirement, so no need to double insulate since mobile devices are not connected to mains power. Usually only the chargers need double insulation.

By the way, there's little semantic quirk here. "Grounding" refer to the zero potential reference point, no need to actually connect to "ground"; while "earthing" refers to the protection for current return path that have to be actually connected to "earth".

 

[glsn]

They use one supply polarity (typically "negative" one) as a ground reference and that's it. They don't have literal ground connection. "Double insulation" is safety and regulatory requirement, so no need to double insulate since mobile devices are not connected to mains power. Usually only the chargers need double insulation.

By the way, there's little semantic quirk here. "Grounding" refer to the zero potential reference point, no need to actually connect to "ground"; while "earthing" refers to the protection for current return path that have to be actually connected to "earth".

so then, why do some pieces of a laptop pcb make contact with a sheet of metal of the chasis?
and each of those sections are like copper filled, if it were just for support contact, then they would have not bother to cut pieces of the plastic shielding that allows components of the board to not short with the aluminum sheet

ps: not the best photo, but it shows what I do mean by plastic shielding/cuts of the plastic shielding

 

[Grog6]

The only ground is the power cord, if attached.
Otherwise, system voltages are related to the negative batt terminal

 

[ArdWar]

so then, why do some pieces of a laptop pcb make contact with a sheet of metal of the chasis?

That's how they connect together all the ground points. Tying the chassis to circuit ground point is good practices to minimize potential charge buildup, potential ESD damage, helps with EMC too (especially with the metalized films).

 

[ThaiTaffy]

Many electronics use a method called floating ground which pretty much uses the neutral terminal of a DC supply or battery as it's earth as many electronics cannot be grounded in the manner most people would understand, planes are a prime example fitting a ground rod to something 30,000 feet in the air is not exactly practical even though many systems in them can be considered high voltage. Even the power points in business class for laptops and such would have a working earth loop that works due to the floating ground theory.

 

[Bill_Bright]

how do mobile devices such as laptops, phones and etc, ground themselves?

They don't. As others have noted, they use an isolated and floating, common ground.

It is isolated so it does not expose the user to any voltages, or to any conductors. This is to ensure you don't get shocked from any exposed contacts or circuits. But also, should you put your phone on a metal filing cabinet, for example, no voltage in the phone can be shorted through other devices in the phone and potentially cause a fire hazard.

The ground is floating because it does not tie to Earth ground.

And it is common because the various circuits inside the phone all share a common [floating] ground.

Think about your car, boat or airplanes. There are all sorts of electronics in all of them - especially in aircraft which have an abundance of radio transmitters and receivers, radar and other navigational aids that use high voltages in high current circuits. The rubber tires in our cars insulate the car from the road, and of course, flying aircraft are not grounded to Earth ground. And boat sit in water. Yet occupants, mechanics and service people don't get zapped - kinda important when refueling.

why do some pieces of a laptop pcb make contact with a sheet of metal of the chasis?

It is the same inside all electronics, not just laptops. Inside your PC case, your TV, home theater receiver, etc. there is a "common" ground - typically the chassis, as you noted. Motherboards typically have 5 or 6 mounting points to the common ground, then another ground through every connector. A graphics card is connected to ground through the PCIe slot, through its mounting bracket and screw, and if it requires auxiliary power, through the power cable(s) too. Then the monitor's ground is tied to the PC's ground through the graphics cable. The speakers are grounded to the PC through the audio cables - same with every USB device. They all connect to establish a common (single value/potential) ground.

This common ground ensures there is NO "difference in potentials" (AKA "voltage") between the different ground points. When you have different potentials, you can have current flow. This is caused by different distances through different conductors to ground - thus different resistances to ground. When you tie them all together, they all are equal.

Ensuring there is only one "common" ground in any electronics systems is important for safety reasons - especially where deadly voltages are present. But even in low voltage applications, ensuring a common ground also help eliminate or at least mitigate potential EMI/RFI issues, which can disrupt a circuit completely, and/or cause very annoying "noise" problems in audio and analog video circuits.