Will the new Macbook's USB-C explode if you connect it incorrectly? You need to review your junior high school physics

Why did some consumers buy the wrong USB Type-C data cable and burn their laptops? How to avoid plugging the Type-C interface incorrectly? What are the advantages of USB 3.1? What are the precautions when choosing a USB Type-C data cable?

At Apple's fall conference in October this year, the long-awaited Macbook Pro finally made its debut, with many people cheering and pessimistic about it. In particular, the Macbook cancelled all external interfaces, including the previous generation Thunderbolt interface, SD card reader interface, and HDMI video output port. Apple integrated them all into USB Type-C, based on the USB 3.1 communication standard, which can transfer files and digital media content at a maximum rate of 40Gbps, and also supports high-power power transmission, replacing the original power port.

Apple's logic is not difficult to understand. USB Type-C is the future global standard peripheral interface. However, many netizens are beginning to worry that if one interface realizes multiple functions, it will be a mess. Especially the feature of supporting 100W charging output. If you buy the wrong cable and plug it into the wrong port, the phone will explode, and the loss will be too great. This worry is not groundless. Foreign media theverge has reported that consumers have bought the wrong cable and suffered tragedies.

The buyer from Silicon Valley is called Benson Leung. His Chromebook Pixel notebook has a USB 3.0 port, which looks the same as a regular USB port. He also has a device with a USB Type-C port, which is the same as the one on the newly released Macbook Pro. To test the device, he bought a Surjtech USB adapter cable from Amazon. Unexpectedly, after plugging it in, the device burned up immediately. When the computer restarted, it prompted that the USB controller could not be verified. It seemed that the hardware was broken.

Such accidents are worrying. How unsafe is USB Type-C? What precautions should consumers take when using it? To find the answers, Transcend reporters specifically referred to official documents and consulted industry experts to roughly understand the principles.

What exactly is USB 3.1?

Most of the USB flash drives and mobile phone data cables we have now use the USB2.0 protocol, with a maximum transmission speed of 480Mbps. The next generation is USB 3.0 and the more powerful 3.1, which have increased their speeds by 10 times and 20 times, reaching 5Gbps and 10Gbps respectively. 3.1 has a faster transmission rate than 3.0, and has an additional PD (Power Delivery) function, which can automatically match peripherals to achieve intelligent power supply.

USB 3.0/3.1 has a clear advantage in speed. One reason is that the single-channel transmission rate is faster. Another reason is that two more data channels are added. Compared with one channel, the speed of three transmission channels is of course much faster, but the cost is that the interface becomes more complicated.

The picture above is the definition of Type-C pins used by USB 3.1. It looks like there are 24 contact points, but in fact, in order to support forward and reverse insertion, the pins are symmetrically equivalent.

As you can see from the port picture above, USB 3.1 has three more parts than USB 2.0:

Two high-speed data channels (one pair in the upper left corner, another pair in the upper right corner)

A pair of communication lines for controlling voltage output (the yellow parts CC1 and CC2 in the figure)

Ports reserved for future USB version upgrades (SBU1 and SBU2)

The following figure is a cross section of a USB 3.0 standard data cable made by a foreign netizen. Compared with the 3.1 version, it has one less control line and one less reserved line. The four lines arranged vertically in the middle are fully compatible with USB2.0. The three extra lines on the left and right are the two additional high-speed data transmission channels of the 3.0 standard.

Due to the lack of control lines, USB 3.0 does not support automatic voltage adjustment. USB3.1 has two more control lines to allow devices to coordinate the supply voltage, support 5V to 20V dynamic output, and support up to 100W power output.

This solves the previous doubts of consumers: what if the phone explodes when the output is 100W? USB 3.1 outputs 5V voltage by default. If the peripheral device supports higher voltage input, it will send a signal to the host device. After the two parties negotiate and confirm, the USB 3.1 controller will increase the output voltage.

Some users are still worried that even if the voltage matches, what if the current does not match? If they buy the wrong cable at the store when using a projector, and the device only supports 1A, but the data cable is 4A standard, will it be dangerous? This is a bit unprofessional, and this situation is impossible to happen.

For a power source with a constant voltage, the working current of the data cable is determined by the power-consuming device, not the charging device or cable. The maximum charging current of iPhone 6s is only 1A. When we use a charger and data cable that support 3A output to charge, the current of the data cable is still only 1A. The output current marked on the charger represents the maximum current that the charger can output, not the working current. The same is true for the data cable. 3A means that the data cable can carry a maximum current of 3A.

If you still don't understand, you can refer to the part about Ohm's law in the junior high school physics textbook. The left side of the equal sign represents the current, and the right side of the equal sign is the voltage divided by the resistance. When the voltage remains unchanged, the current is determined by R, and R represents your smartphone. So, there is no need to worry about high-power data cables causing your beloved electronic devices to explode.

Some older smartphones do not support USB 3.0/3.1, but still use the Type-C interface. Is it dangerous to mix old and new devices? Don't worry. Although the phone supports the Type-C interface, the internal control line is not actually used. Due to the lack of charging negotiation process, when plugged into a new Macbook, the interface will only output the default 5V voltage, and it works the same as USB 2.0.

As for other devices, the same principle applies. USB 3.1 automatically matches the voltage and the communication rate, so consumers don't have to worry about it. For devices that support the 3.1 protocol, the interfaces communicate and negotiate the transmission rate and power supply voltage. For USB 1.0 and USB 2.0, compatibility can also be achieved by selectively giving up the use of certain lines.

If the USB interface is used to transmit HDMI video signals, how should the video cable and data cable be distinguished? The answer is no, they are actually the same inside. The three high-speed data channels in USB 3.1 can transmit word documents, so why can't they transmit video data to a TV or projector at high speed? In technical terms, this is called 'port multiplexing'.

However, the American buyer's laptop accidentally burned up, wasn't it because he used the wrong data cable? How to explain this? The answer is at the bottom of his long review. Pay attention to the content in the red box. The gist is as follows: I used a Type-C development board and a multimeter to carefully study this data cable. It turned out that the manufacturer connected the cable incorrectly. The negative and positive poles of the power supply were connected in reverse.

With such a low-level mistake, it is no wonder that the data cable has received the lowest rating of 0.5 stars and the product has been removed from the shelves.

Of course, ordinary data cables cannot support 100W or even 60W of power. For this reason, a chip needs to be packaged to tell the USB 3.1 controller in the new Macbook its maximum carrying capacity.

How should I choose?

This is a USB Type-A to Type-C data cable. This cable undoubtedly supports USB 2.0. Whether it supports USB 3.0 and 3.1 depends on the interface and the internal design of the cable.

The connector on the left in the above picture is a regular USB Type-A. If it only has 4 contacts, it only supports USB 2.0. If it has 9 contacts, it may be able to achieve USB 3.0 and 3.1 transmission speeds, but the output voltage can only be the default 5V.

The left side of the above picture shows the USB 3.0/3.1 Type-A plug definition, and the right side shows the USB 3.1 Type-A socket definition. The two are fully compatible, but when observing the socket, it can be found that there are no power control line contacts, which shows that the Type-A connector does not inherently support intelligent voltage regulation.

To buy a truly full-featured USB 3.1 data cable that supports high-speed transmission and voltage regulation, one necessary condition is that both ends use a multi-contact interface such as Type-C, and the other is a built-in chip. You have to ask the merchant whether there is a chip or not, because you really can't tell from the appearance.

So if you want to save trouble, just buy a Macbook with a built-in chip and USB Type-C on both ends, which is enough to handle most peripherals. If you really need a higher transmission power, then buy it based on your needs. But even if you buy the wrong one and mix them up, it’s okay. The USB 3.1 controller will communicate with the chip inside the data cable, and the output power will not exceed its carrying capacity.

The only thing you need to worry about is buying a counterfeit power cable and using cheating methods to deceive the USB 3.1 host controller. However, the actual power carrying capacity does not meet the requirements, and there is indeed a risk of overheating and fire.

As a winner of Toutiao's Qingyun Plan and Baijiahao's Bai+ Plan, the 2019 Baidu Digital Author of the Year, the Baijiahao's Most Popular Author in the Technology Field, the 2019 Sogou Technology and Culture Author, and the 2021 Baijiahao Quarterly Influential Creator, he has won many awards, including the 2013 Sohu Best Industry Media Person, the 2015 China New Media Entrepreneurship Competition Beijing Third Place, the 2015 Guangmang Experience Award, the 2015 China New Media Entrepreneurship Competition Finals Third Place, and the 2018 Baidu Dynamic Annual Powerful Celebrity.