The Principle of Reverse Wireless Charging in Phones
- Electromagnetic Induction
Traditional electromagnetic induction wireless charging is based on Faraday’s law of electromagnetic induction. When an alternating current is passed through the transmitting coil, it generates an alternating magnetic field. When the receiving coil is placed in this magnetic field, an induced electromotive force is generated, thereby charging the device. This principle is well-established and commonly used in many devices that support wireless charging. However, electromagnetic induction wireless charging requires precise alignment of the transmitting and receiving coils, and the charging distance is very short, usually only a few millimeters.
- Magnetic Resonance
Magnetic resonance wireless charging is a special case of electromagnetic induction. It utilizes the principle of electromagnetic coupling resonance. By setting up LC resonant circuits in both the transmitting and receiving ends and tuning them to the same frequency, magnetic resonance can be generated to achieve efficient energy transfer. Compared with electromagnetic induction, magnetic resonance wireless charging has the advantages of a longer effective charging distance, up to tens of centimeters, and the ability to charge multiple devices simultaneously, offering greater flexibility and freedom.
Devices That Support Reverse Charging
- Headphones
Nowadays, many true wireless stereo (TWS) headphones come with wireless charging capabilities, such as Apple’s AirPods 2nd generation and Huawei’s FreeBuds. These headphones come with wireless charging cases that can be conveniently charged via phones that support reverse wireless charging. For example, the reverse wireless charging function of the Huawei Mate 20 Pro can be used to charge TWS headphones.
- Smartwatches
Smartwatches are also increasingly adopting wireless charging functions, such as Apple’s Apple Watch and Huawei’s smartwatches. If a user’s smartwatch runs out of power while outdoors or traveling, they can use a phone with reverse wireless charging capabilities to provide temporary power.
- Other Phones
Some flagship phones support reverse wireless charging and can charge other phones that support wireless charging in emergency situations. For instance, phones like the Huawei Mate series and the Samsung S10 series support reverse wireless charging, serving as a temporary rescue solution when a friend’s phone is out of power.
Efficiency and Heating Issues in Practical Use
- Efficiency Issues
The efficiency of reverse wireless charging is not particularly high, generally ranging from 30% to 60%. This means that the phone’s own power consumption can be relatively high. For example, the Huawei Mate 60 Pro has a wireless reverse charging power of 7.5W. However, when using it to charge other devices, the phone’s own power consumption may exceed the actual output power.
- Heating Issues
When using the reverse wireless charging function, it is common for the phone to heat up. During the charging process, the temperature of the phone’s back may rise above 45℃, especially in summer or high-temperature environments. This may trigger the phone’s overheating protection mechanism, interrupting the charging process and affecting charging efficiency and device safety.From the above content, it can be seen that while reverse wireless charging technology provides convenience for our lives, there are still some limitations in practical use. Understanding its principles, applicable devices, and practical issues can help us better utilize this function in daily life.
How to Improve the Low Efficiency of Reverse Wireless Charging
The low efficiency of reverse wireless charging is mainly due to energy losses during electromagnetic transmission as well as hardware and software limitations of the devices. Here are some methods to improve the efficiency of reverse wireless charging and the latest research progress
Optimizing Circuit Design
The efficiency of reverse wireless charging can be effectively improved by optimizing the circuit design. For example, adopting a multi-mode combination circuit control strategy, such as the combination of modes Ⅰ, Ⅱ, Ⅲ, and Ⅳ, can adjust the working mode according to different pulse densities to optimize energy transmission efficiency. In addition, for LCC/LCC type bidirectional wireless charging systems, adjusting the conduction angle and the phase difference of the drive signal can significantly reduce the fundamental voltage phase shift angle, thereby improving the system’s power factor and operating efficiency.
