Vivo's multi-coil high-power wireless flash charging technology revealed

With the development of wireless charging technology, the application of wireless charging function in electronic devices is becoming more and more popular. Electronic devices with wireless charging function are becoming more and more popular among users. Currently, wireless charging has become a standard feature of flagship phones from major manufacturers.

For example, Apple, Huawei, Xiaomi, etc. have all applied wireless charging technology to their latest flagship phones. In addition to wireless charging, wireless reverse charging technology has also become a black technology in the mobile phone industry. Compared with Huawei, Xiaomi and other manufacturers, vivo is slightly weak in wireless charging. For example, its flagship models in 2020 are not compatible with wireless charging. Perhaps wireless charging technology is not yet perfect, or it may not be the focus of vivo at present.

Despite this, vivo's R&D department is still developing related technologies for wireless charging for application in subsequent models. At present, wireless charging solutions based on the Wireless Charging Alliance standard are generally single-coil system charging solutions, which have limited output power. The maximum output power is the maximum output power that a single-coil charging circuit can provide. For example, the maximum output power of many single-coil charging circuits can only support 40W, and the charging power is relatively low.

In order to improve the charging efficiency of charging equipment, vivo applied for an invention patent called "A wireless charging device" (application number: 202010362537.8) on April 30, 2020, and the applicant was Vivo Mobile Communications Co., Ltd.

Based on the information currently disclosed in the patent, let's take a look at this wireless charging system design.

As shown in the figure above, it is a structural block diagram of the wireless charging device of the patent application, which includes N charging circuits 11, each of which has a transmitting coil. When the charging device charges a mobile phone, M of the N charging circuits can be allowed to work at the same time, which has a higher charging power than a single charging coil, thereby improving the charging efficiency.

However, there are also conditions for these charging coils to charge mobile phones at the same time. We know that wireless charging is similar to a communication method and needs to work at a specific frequency. For example, if two charging circuits start working, each charging circuit has its own operating frequency. Only when the operating frequencies of the two are the same and the difference between the operating frequency of the first charging circuit and the frequency of the ASK (amplitude shift keying) signal is greater than the threshold value, or when the operating frequencies of the two charging circuits are different and the difference between the operating frequencies of the two charging circuits is greater than the preset threshold value, can the two charging circuits start working normally.

In the scenario envisioned by the patent, not only can the wireless charger have multiple charging circuits, but also multiple receiving coils and receiving chips can be set in the mobile phone device, and each chip controls a coil. When the wireless charging device charges the mobile phone, one coil corresponds to one transmitting coil, so that the receiving coil converts the magnetic field energy into electrical energy under the action of the AC magnetic field generated by the transmitting coil to generate AC power and transmit it to the receiving chip, which can convert AC power into DC power to supply mobile phones and other devices.

In this process, the charging circuit includes components such as the transmitting coil and the resonant capacitor. When power is transmitted, the signal transmission gain must be considered. The signal gain is related to the operating frequency of the charging coil, as shown in the figure above.

is the resonant frequency of channel A, is the resonant frequency of channel B; the closer to the resonant point, the higher the system gain value and the higher the energy that can be obtained, the wireless charging system controls power transmission by adjusting the operating frequency based on this principle.

As we mentioned above, channels A and B are not limited to working within a certain frequency range, but can also work at two independent fixed frequency points. In this way, the two can adjust other parameters, such as frequency modulation, voltage modulation, duty cycle adjustment, etc., to achieve multi-channel wireless charging by adjusting these settings, thereby improving charging efficiency and reducing the voltage ripple (the industrial frequency AC component contained in the output DC voltage) on the same input power supply.

The above is the wireless charging device and system invented by vivo. By setting up multiple charging circuits in the charging device, multiple charging circuits are allowed to work at the same time, thereby increasing the charging power. In the charging receiving device (smartphone), multiple receiving coils are also set to correspond to the multiple charging circuits of this wireless charging device, so as to better play the effect of this charging device.