Wireless charging applications that reduce charging energy consumption

[Introduction] Wireless charging technology is not new. It is just that the design scheme was limited in the early days because wireless charging technology could not achieve high power, high-speed charging and safety considerations. Therefore, wireless charging technology could only be applied to low-power and small-power designs.

Wireless charging is not a new technical solution. In fact, there are a lot of wireless charging applications in our daily life, such as electric toothbrushes, electric shavers, and other consumer electronic devices. However, the difference in charging efficiency and safety when using wireless charging applications has not been effectively improved. Until now, with the integration of microcontroller applications, wireless charging has achieved higher charging efficiency and better practical value...

Wireless charging technology is not actually new. It is just that in the early days, due to the inability of wireless charging technology to achieve high-power, high-speed charging and safety considerations, wireless charging technology could only be applied to low-power and low-electricity designs. For example, in the design of electronic products that need to be waterproof and dustproof, wireless charging technology can be used to eliminate the need for exposed metal charging connectors in the design, such as in the design of electric toothbrushes, electric shavers and other products.

The wireless charging solution uses the Tx-end coil to form an electric field, and then the Rx-end coil inductively converts energy for wireless power transmission. Texas Instruments

In order to enhance the efficiency of energy transmission, the design and size of the coil will also affect the transmission performance. The picture shows the wireless charging coil module developed by TDK. TDK Corporation

Wireless charging technology with no contacts or wires for energy transmission is suitable for high-durability design solutions

Basically, in low-power charging applications, wireless charging technology can be said to be a fairly common application solution. It can be mainly used to solve the application needs of weather-resistant, waterproof/dust-proof electronic product designs. However, when wireless charging technology is used in such electronic products, there is no need to overly demand charging performance. At the same time, due to low power, higher application safety can be achieved. Naturally, the technology does not need to improve the existing usage solutions to meet design requirements. However, if the design product is replaced with a smartphone, digital camera/camcorder or a mobile device with a higher capacity battery, the old wireless charging technology will not be able to meet the design requirements.

First, let's examine the problems that battery-powered devices often encounter when charging. The key to the energy consumption of battery chargers can be examined from two aspects: charging efficiency and standby power consumption. In terms of standby power consumption, many users often use the charger to plug the device into the power supply circuit after the device is fully charged. This means that the charging environment will generate a large amount of additional standby power consumption (i.e. no-load power consumption). In addition, in order to save costs, the circuit design of the charger is relatively simple. Often, the energy consumption generated by the device charger when it is no-load is almost the same as the energy consumption during charging!

Wireless charging technology has effectively improved the energy consumption of chargers when not in use

When designing wireless charging solutions, the no-load energy consumption problem must be optimized and improved so that the charging system can achieve more effective energy-saving benefits when upgrading the wireless application environment. At least, the meaningless no-load power consumption problem can be improved. This has also become a key value-added benefit for increasing the introduction of wireless charging applications. The current new generation of wireless charging systems has a no-load power consumption design for the Tx (Transmitter) solution. The current no-load power consumption can reach less than 100mW, which has greatly exceeded the no-load power consumption performance of general traditional chargers.

For wireless charging applications, charging efficiency is another key factor that affects power consumption, because the higher the charging efficiency, the faster the charging process can be completed. With the current wireless charging solution, wireless transmission cannot be compared with direct copper cable transmission performance, but the current wireless technology solution can achieve more than 70% of wireless transmission performance. If more efficient components can be used in the wireless charging Rx (Receiver)/Tx (Transmitter), the performance of this wireless charging can be further improved.

Wireless charging solutions can save energy by charging multiple devices simultaneously

When discussing wireless charging applications, people are not only concerned about the more dazzling and convenient IT/3C peripheral charging benefits, but also whether the upgraded wireless charging solution will increase the overall power consumption due to daily charging needs? Basically, this must be examined from many aspects, because the power consumption statistics of electronic products will have a huge calculation gap due to different user habits and charging application methods. If the evaluation takes the default application scenarios of most users as the basis, for example, a set of wireless charging Tx is selected to replace several chargers (currently wireless charging Tx can support simultaneous charging of multiple Rx devices), the introduction of wireless charging solutions will be more effective under this usage basis, because it saves more than one set of wired chargers and saves the waste of no-load power consumption of several wired chargers.

For AC chargers that meet the "Energy Start" green energy application label, the energy conversion efficiency of a 5W charger is about 70~75%, and the average power consumption of a 5W charger is generally 0.1~0.15W. If the user has bad habits, most users will not unplug the charger after charging, but will continue to plug the charger into the power socket for a whole day or even for several months. This usage scenario will cause a huge loss of power consumption during the entire process!

Traditional chargers have low unit prices, but no-load energy consumption often results in greater waste

For example, if a 5W charger consumes about 2~3W of power during charging, and the higher 3W is used to calculate the one-hour charging time, with a design solution of 70% energy conversion efficiency, it means that 4.3W of power is consumed during the charging process. If the charger is plugged into the power socket for a whole day (i.e. 23 hours of no-load/1 hour of charging process), it means that 0.15W of power is lost every hour in 23 hours, and a total of 3.45W of energy is generated in 23 hours. The energy consumption during charging plus the no-load energy consumption equals a loss of 7.75W for the whole day.

From the calculation process, it can be found that the energy consumption of traditional chargers will be wasted due to the energy consumption of standby no-load. If two chargers are used in similar usage scenarios, it means that the two chargers will consume 15.5W of energy in a day. Based on this, when comparing wireless charging solutions, even though the power transmitted through the wireless mechanism currently has a power loss of nearly 30%, because the wireless charging pads of multiple charging devices are integrated, as long as the no-load power consumption can be effectively reduced to 100mW, as long as there is more than one set of wired charger application conditions, the overall power consumption of wireless chargers can be significantly better than that of wired charger solutions.

Wireless charging technology is complex in design. Coil size, angle, and transmission method will affect energy transfer.

Let's look at the principle and structure of the wireless charging design. The wireless charging solution mainly uses the inductive coupling process to transmit power wirelessly after energy is converted into wireless transmission. Basically, the Tx (transmitter) passes the alternating current through the coil to form a magnetic field, and then uses the Rx (receiver) coil to induce a voltage difference. This voltage difference formed in the Rx coil through the wireless process can be used to directly drive the power supply of electronic devices, or form a power source for charging batteries after conversion and transformation through the Rx line.

As for the transmission efficiency of electric energy, it is actually determined by the difference in the coupling (k) value and the quality (Q) parameter between Tx/Rx. There are many key factors that affect coupling and quality, such as the distance between Tx/Rx, relative size, coil design, coil angle, coil shape, etc.

Generally speaking, there are many ways to improve the energy transmission efficiency of wireless charging, such as reducing the distance between Tx/Rx as much as possible. The shorter the distance, the higher the wireless charging performance! In addition, the larger the difference in coil size between Tx/Rx, the lower the energy transmission efficiency will be. If you want to achieve the goal of high-efficiency energy transmission of wireless charging, due to the limitation of energy transmission, you should reduce the distance between Tx/Rx as much as possible, and design the coils of Tx/Rx as close to the same size as possible to achieve the best transmission efficiency.

Wireless charging solutions have been greatly improved in terms of safety and practicality

However, when designing wireless transmission application solutions, if the transmission energy density increases, it also means that the energy loss caused by the transmission process will be lost in the form of heat. In other words, the higher the transmission energy, the more heat generated during the charging process. For the design of wireless charging solutions, system problems should be optimized to the maximum extent. By reducing power loss, the heat problem generated during the charging process can also be further improved. If the charging energy density is increased to improve the charging efficiency, but an active heat dissipation design (such as a fan) must be set for the Tx and Rx, this will cause additional power consumption waste by forcibly driving the fan for heat dissipation, which conflicts with the energy saving design purpose of the overall charging system.

Another common problem with wireless charging solutions is the EMF (Electric and Magnetic Fields) problem. Wireless charging generates an electromagnetic field at the Tx end, which inducts and converts wireless energy with the Rx end coil through the formation of the electromagnetic field. In order to enhance the charging performance, the electromagnetic energy of the Tx must be enhanced. Even the environment we live in is full of electromagnetic fields of various intensities. In fact, the electromagnetic field generated by the wireless charging Tx will also cause health concerns for users.

Taking wireless charging solutions as an example, the electromagnetic spectrum used is generally non-ionospheric segment, and the electromagnetic field that is significantly harmful to the human body is mainly in the ionized segment. The radio wave energy in the non-ionospheric segment is usually very small and has little effect on human tissue. At present, most wireless charging solutions also focus on user application safety issues and conduct certification audits based on user concerns, which can also minimize concerns about safety of use. For wireless charging applications, in addition to bringing more convenient use of 3C electronic products, the introduction of safer intelligent control and high-efficiency active intelligent adjustment of charging energy design during charging applications can not only make full-load charging safer, but also reduce the no-load power consumption of charging equipment to a lower level, and long-term use can also achieve the purpose of energy saving.