What exactly is fast charging?

1. Definition of fast charging

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There is currently no clear definition of fast charging by any relevant organization, and everyone has their own understanding of fast charging.

Fast, as distinguished from slow, can only be judged based on a reference.

The USB standard power supply voltage is 5V. If the iPhone 11 uses Apple's 5V1A 5W charging, it is definitely classified as slow charging. However, if it uses the APPLE2.4A protocol to achieve a charging power of 12W, or uses USB-C to Lightning to obtain more than 18W of power through a PD charger, both of which are fast charging.

In terms of Android lineup, increasing the voltage through QC can also be classified as fast charging. VOOC, SCP and other low-voltage and high-current charging are also fast charging. PD ultra-high power charging is of course also fast charging.

Simply put, any method that uses different means to increase charging power can be summarized as fast charging.

2. When did fast charging come out?

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As early as the Nokia era, the means of maintaining the battery life of electronic products mostly involved replacing batteries. At that time, electronic products had single functions and low power consumption. One battery could be used for several days. It was normal to carry several batteries to extend the battery life. It can be said that there was no demand for fast charging in the market at that time.

It was not until the launch of the Samsung Note giant-screen mobile phone that the matching charger had strange specifications for the first time. The output voltage was not 5V but 5.3V, and it had a line loss compensation function to offset the voltage drop loss of the wire to increase the charging power. At this time, users found that this charger charged much faster than other 5V chargers, and with a fast and slow comparison, the experience of "fast charging" was vaguely born for the first time.

In 2014, OPPO launched the Find7 mobile phone equipped with VOOC flash charging. It was popular that charging for five minutes could provide two hours of talk time, but only OPPO users enjoyed this pleasure. In 2015, Qualcomm QC2.0 mobile phones were launched in large numbers. Based on the universal technical standards and a variety of third-party accessories, fast charging officially kicked off, and most users enjoyed the pleasure of fast charging for the first time.

3. USB-C unification promotes the development of PD fast charging

As early as December 2013, the US USB-IF Association announced the USB-C interface, and the relevant industry chain was ready for large-scale mass production in 2014. The USB-C interface supports double-sided blind insertion, which solves the experience of the device end observing the front and back before inserting. The 24-pin pin allows the interface to support 100W power transmission and 20Gbps data transmission, and the PPS voltage subset was added to the later PD3.0 standard, which has sustainable development potential.

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In 2015, many products equipped with USB-C were launched for the first time, including the first USB-C mobile phone LeTV Super Phone 1, the first USB-C notebook New Macbook, the first tablet Nokia N1, the first USB-C charger Apple 29W, and the first USB-C power bank Yubo YB-CP1. These pioneers have contributed to the rapid popularization of USB PD in the future.

The grand unification of the USB-C interface has brought vitality to the industry. Various PD fast charging accessories are inexpensive and of high quality. After several years of market development, USB PD fast charging has entered almost all mainstream electronic products in 2020.

4. Composition of the fast charging system

The fast charging system consists of three major components: the charger (power adapter) responsible for providing power, the cable (data cable) used for power transmission, and the receiving device (digital product). Each of them is a participant in the fast charging system.

1. Fast charging charger

In the past, each device required a corresponding charger because of different voltage requirements and interfaces, and the power strip was densely packed with different chargers. Now, the advanced communication mechanism of USB PD allows different devices to communicate with the charger and request the voltage that matches their needs. Whether it is a high-power laptop with up to 100W or a TWS headset with only a few watts, they can all be charged with the same PD charger, and multi-port chargers can also provide one-to-many services.

From the device perspective, traditional silicon-based chargers are bulky and inconvenient to carry. If you want to reduce the size of the charger, you must increase the switching frequency, but traditional silicon-based semiconductors cannot meet high-frequency characteristics, so the size of the charger has always remained at a large level.

In 2018, ANKER successfully mass-produced the first gallium nitride charger, heralding the entry of chargers into another dimension. The high frequency and high efficiency of gallium nitride chargers can use smaller transformers, capacitors, inductors and other devices. Combined with the three-dimensional stacking design, the size of gallium nitride chargers is nearly half that of traditional chargers at the same power.

2. Fast charging cable

In addition to a charger, fast charging also requires a data cable. The data cables used for fast charging are mainly divided into three types: USB-C to USB-C, USB-C to Lightning, and USB-C to USB-A.

USB-C to USB-C is also known as CC cable. According to the cable specifications and whether it has a 5A E-Marker chip, it can be divided into 60W power transmission cable and 100W power transmission cable. If the user needs to use more than 3A current, it must be used with a 5A E-Marker cable. CC cable has become the most common cable for Android phones, tablets, and laptops.

USB-C to Lightning is a special cable launched by Apple for connecting to PD chargers. Applicable devices include iPhone, AirPods, mid- and low-end iPads and other Apple devices. As a Lightning cable, each one needs to pass MFi certification.

There are two types of USB-C to USB-A. One is a special specification mainly used for some special fast charging devices, such as Huawei's low-voltage fast charging SCP, OPPO's low-voltage fast charging VOOC, and Xiaomi's private magic fast charging; the other is a universal cable. The universal cable does not support PD fast charging, but only supports QC, AFC, FCP, PE and other fast charging.

3. Equipment

In 2020, most digital products support fast charging. Mainstream devices such as Android phones, iPhone 8 and later models, iPads, notebooks, game consoles, TWS headphones, smart wearables, etc. all support USB PD charging.

5. Future fast charging technology core

Let's take the mobile phone with rapid development of fast charging technology as an example. A few years ago, the QC fast charging power of mainstream mobile phones stagnated at 18W for a long time, and the full charging time was about 2 hours. As for why it has been maintained for many years? That's because it's okay to use, but the heat brought by the low-cost, simple and crude QC high-voltage fast charging is not a good experience. So Huawei and OPPO began to take the low-voltage direct charging route, which is faster and does not generate too much heat. Compared with QC, it has a great advantage, and the charging speed is about 1 hour, which has been improved to a certain extent.

The following technologies used in fast charging have become stable and mature. Compared with the previous slow evolution, they have reached the level of cross-generational upgrades and can be defined as fast mainstream technologies in the next few years or even decades.

1. Charge Pump

Fast charging technology made a major step-by-step leap in 2017. Meizu launched the 55W Super mCharge fast charging technology for the first time in the world at MWC 2017, demonstrating the charge pump technology that was very advanced at the time, and providing technical verification value for various fast charging development routes in the future. The charge pump chip can provide a voltage division function. The charger increases the voltage for transmission, no longer requiring thick wires to transmit large currents, reducing line losses, and then entering the mobile phone and being converted into low-voltage high currents through the charge pump. The entire system is extremely efficient, far exceeding other step-down ICs.

2. Series direct charging technology

In 2018, OPPO launched the 10V5A high-voltage direct charging technology for series-connected batteries. The conversion circuit that causes heat in the mobile phone was moved to the charger. The two 4.4V batteries were connected in series to become an 8.8V battery pack. There is no large voltage difference between the charging voltage and the battery pack voltage, achieving both low heat and fast charging.

3. Graphene-based batteries

In 2020, the core battery of fast charging finally ushered in a material change. The large-scale production of graphene-based batteries has allowed ultra-high-power fast charging to be free from PPT drawings. Combined with charge pump and series charging technology, the charging power of mobile phones has exceeded the 100W mark for the first time in history, and even surpassed the power of laptops. OPPO, VIVO, and Xiaomi have successfully mass-produced flagship mobile phones with fast charging of more than 100W, and the charging speed is calculated in minutes.

Summarize

The three major performance selling points of mobile phones in 2020 are processors, cameras, and fast charging. Charging has gone through a long process from being insignificant at the beginning to becoming a key module of digital products. It only takes tens of minutes to quickly restore power for digital products to continue using. From a technical point of view, the huge market demand for fast charging of electronic products has promoted the development of the industrial chain, accelerated the research and development of materials science, and the gradual reduction in mass production costs ultimately benefited consumers. Ultra-high-power fast charging makes you unaware of its existence, and it is fully charged before you come to your senses, silently reducing the user's waiting time and enjoying life to the fullest.