How does a USB port work?
USB charging explained
Charging with a USB port has become routine for all gadgets. Ten years ago, you would have checked if the hookup on your gadget worked with your charger before you buy it. Today, most use micro-USB, except for Apple using the Lightning connector. And now we are starting to see more and more USB-C connectors to charge laptops.
Today you can charge your e-reader with your computer, charge your phone with your friend and connect your camera to your TV all thanks to the standardization of the connectors and the associated USB Charging Cable.
The problem today is the variety of USB charging ports. Chargers, connections and cables are not all the same. You have probably noticed that some wall chargers are more powerful than others. Some USB ports of laptops seem more powerful. And on some desktops, some ports can charge a device even if the computer is turned off. There is a reason for that. But before, let's look at how USB charging works. There are 4 USB specifications: 1.0, 2.0, 3.0 and 3.1 with the addition of the USB-C connector. They differ significantly., We will focus on the USB 3.0 because it is the most common. With a USB connection, there is a host and a device. In most cases, the PC is the host and your tablet, smart phone or camera is the device. Current flows from the host to the device, but data can move in both directions, for example, when you transfer data from your smartphone to your PC.
A USB 1.0 or 2.0 port has four pins of contacts and a four-wire USB cable. The internal pins carry the data (D + and D-) and the external pins carry the electric current of 5 Volts. USB 3.0 ports add 5 pins, so USB 3.0 compatible cables have 9 wires. In terms of current (milliamperes or mA), there are 3 types of USB ports according to the current specifications: a standard transfer port, a charge transfer port and a dedicated charging port. The first two are on your computer and the third is for wall chargers.
In the USB 1.0 and 2.0 specifications, a standard charging port can pounds up to 500mA (0.5A), In USB 3.0 it can reach 900mA (0.9A) The dedicated charge port can deliver up to 1,500mA ( 1.5A). USB 3.1 increases the bandwidth to 10Gbps so-called SuperSpeed + mode which is almost equivalent to the first generation Thunderbolt. It also supports a power of 1.5A and 3.0A on a line of 5V.
USB-C uses a different connector that is universal, which means that it does not have a specific meaning and like the Apple Lightning connector, the USB-C can double the bandwidth of USB 3.0, at the same time as it increases the charging power. Apple has paired USB-C and USB 3.1 on its new 12 "MacBook, and has also started appearing on smartphones, the first one being the OnePlus 2. Other popular models such as Google's Nexus 6P, OnePlus3 and the Samsung Galaxy Note 7. There may be old-style USB ports that support the standard 3.1.
The USB specification also allows for a "standby and charge" port, while a powered-off computer can leave a charging port on. You may have noticed it on your desktop computer while the power continues to flow through the master card. Some laptops have "sleep and charge" ports.
That's what the specification dictates. On the other hand, many USB chargers do not conform to these specifications, most are wall chargers. Apple's iPad charger, for example, provides 2.1A on 5V and Amazon's Kindle Fire charger provides 1.8A. Many car chargers can provide between 1.0A and 2.1A.
The variance between a normal 500mA USB port and a dedicated charging port that can go up to 3,000mA makes us ask the following question: if your phone comes with a 900mA wall charger and you plug it into an iPad charger 2,100mA, will it damage or explode the battery?
The short answer is no. You can plug any device with any cable into any charger and it will not work. Using a more powerful charger will only reduce the charging time.
The long answer is that the age of the device plays an important role, involving the charging speed and whether it can be charged with a wall charger. In 2007, the USB Implementers Forum released the Battery Charging Specifications, which standardized a faster way to charge USB devices, either by increasing the number of amperes passing through your PC's USB port or using a wall charger. Soon after, those who marketed USB devices implemented these specifications.
So if you have a modern USB device, you can use a high amperage USB port to enjoy faster charging. For older devices, however, it will probably not work with a USB port that uses the standard Battery Charging Specification.
A few things to remember. Computers can have two kinds of USB ports: standard downstream or downstream. Manufacturers do not always tell them. The result is that you could have one device that charges on one port of your mobile and not on the other. You will see this on older models. Most manufacturers have a lightning bolt over the port to charge a device, and in some cases these ports can charge even when the phone cover is closed. Some external devices such as 3.5-inch hard drives require more power than a normal USB port can provide. That's why they include a second USB Y port to provide more power or an AC adapter. Charging with USB has become easier over time and if the new USB-C connector is gaining popularity, it will be even easier since you will not have to pay attention to the direction of the plug to connect.