Why exactly 5V voltage in adapters for smartphones?

Question

Batteries

Very interesting, but could not find the exact information on the net. Adapters almost always indicate a voltage of 5V, which is why this value is the most common in this segment. And an additional question, if there is an opportunity to find out: in simple words, how can you raise the voltage to 12v-20v using quick charge and not ruin the board?

Answer 1

And what, exactly, is the question? Why is 5 chosen as the standard and not 4 or 6? Or, say, 12, 24, 36 or 100 volts?
You need to understand that there is such a thing as Ohm's law. Current is directly proportional to voltage and inversely proportional to resistance. Resistance is a property of a conductor, it depends (if not too deep) on what kind of metal, on its thickness and length. And we always have a limited power source of current.
Power is the amount of energy that is consumed, converted or transmitted per unit of time.
Here we have a cable and we need to transfer 5 watts through it in order to quickly charge the smartphone. How kraz turns out 5 volts * 1 ampere = 5 watts. That is, a current of 1 ampere should flow through our cable. This is a fairly large current, and if our cable has too much resistance (that is, it is long, or thin, or not made of copper), then most of the transmitted energy will be spent on useless heating of the cable.
If you want to double the power in order to charge the smartphone even faster, you will either have to double the current, and at the same time, the energy will quadruple (after all, the dependence on the current is quadratic) that goes into heating, and to prevent this from happening, you need to make the cable thicker, cover it with silver ( which has low resistance), make the wire shorter. All this is expensive and inconvenient.
The second option is to double the voltage, then at a voltage of 10 volts and the same current of 1 ampere, 10 watts of power will be transmitted with the same losses for heating the wires.
It turns out that by increasing the voltage, it is possible to reduce the losses for energy transmission along the same thin ones. flexible inexpensive wires, as before, BUT!
But. The higher the voltage, the higher the requirements for insulation between conductors with different potentials. And chemical sources usually do not produce such a large voltage, you have to turn them on in series, which makes it difficult to balance during charge / discharge, dimensions, structural complexity of the elements ... In addition, pn-junctions in transistors and diodes are not able to withstand large voltage, because breakdown may occur. The same problem can occur in inductors and capacitors. Capacitors are getting bulkier, more insulation is needed, and transistors can't be made very small.
It turns out such a dilemma. Electronics balances between current and voltage as between Scylla and Charybdis, trying to save on this and that.
Where high power is needed, it is necessary to turn up the voltage. That is why we have 220v in the outlet, and 380 between the phases. To boil a two-kilometer kettle, you have to pass a current of almost 10 amperes, but it is important for us that the kettle is heated, and not the wires from the outlet to the kettle and in the walls. Therefore, the wires are thick, much thicker than your charging cord from a mobile phone or the tracks on the board inside it.
Where logic is mainly important and power is not required much, only to illuminate the screen or a bright flash LED, a small voltage of 5 V is selected. In processors and in general in integrated circuits, it is necessary to use an even lower voltage of 3.3V so that very closely laid tracks inside do not break through. Reducing the voltage even more is already problematic, since there are restrictions from below on the opening of pn junctions. There is simply not enough voltage to transfer electrons in the semiconductor layers.
So electronics are not alive with 5 volts alone. Somewhere, for example, to power LEDs, voltage is not as important as current. It must be within the specified limits, since having exceeded the ability to dissipate heat, we will literally burn the pn junction, so we have to vary the voltage so that the current remains within acceptable limits.
In a car, the standard is 12 volts and in many trucks 24. I already spoke about the socket and there is a separate topic why and how the electrical networks of different countries are arranged. There is a whole zoo of stresses in your laptop and smartphone. Previously, there were even devices where the backlight of the screen required several kilovolts.
At the same time, the power is not large, and the insulation is designed so that nothing breaks through, but this is a separate circuit inside the device, and in each place you need the voltage for which the corresponding sections of the circuit are designed.

Answer 2

5v is the USB standard , and quick charge raises the voltage only after successful negotiations with the device. If the connected device does not know how to increase the voltage, then charging should not raise it.

Answer 3

5V is some industry standard that is compatible with USB and allows you to safely charge the battery, where the voltage is about 3.7V.
Quick Charge - and other fast charging options are not so easy to implement, but if the question is why the board is not on, it's simply because it is designed for such a voltage. Starting from the parameters of the element base, the wiring of the tracks and ending with the logic of charging the batteries (note that often in this case there is more than one battery).

Answer 4

5 V is a story 50-60 years ago with the supply voltage of one of the first series of "logical" microcircuits. For speed, they had a low breakdown voltage of the transistors (see Sergey Pankov 's post ) and the supply voltage was chosen "round and smaller". And then, as usual, - legacy.

Answer 5

before, microcircuits fed either 3.3 or from 5, there were still those that held 9-15, but this is a completely different technology
from there,
if it’s so interesting, the
versions of microcircuits of the 133 555 561 series were googled
, I just grew up with this

Answer 6

The beginning of 5 volts was laid due to the widest distribution of digital TTL logic, such a value was obtained as the most appropriate for its circuitry (by the number of direct silicon PN junctions involved in the circuits). Details of why it was done this way and not otherwise can be found in the books of V. Shilo, who wrote a lot about digital circuitry.
This baton was picked up by the USB port. And also thanks to its widest distribution, this voltage began to be used even in circuits not directly related to USB and TTL.
Well, the spread of 4-volt lithium batteries, again the widest, put an end to it - it turned out to be very convenient to build lithium chargers from 5 volts.
As for the charger's ability to raise its output voltage to 12 volts or more - this is not directly related to the origin of 5 volts and is more due to the fact that chargers have become "smart", i.e. having their own processor with their own program, into which quite complex functionality can be stuffed.