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Who can think that the mobile phone industry will affect the environment? When you think about how to reduce ecological pollution, the idea may be to change the car design, or use green energy, it will not be a mobile phone. However, we do see that mobile phone chargers have a big impact on the environment. The mobile phone industry has begun to use the Universal Charging Solution (UCS) to solve this problem, and UCS will change the way mobile phone manufacturers design mobile phones. This article will analyze the factors that need to be considered to implement a secure charging interface.
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A mobile phone user produces about 17 kilograms of carbon dioxide a year, which is equivalent to a car driving 111 kilometers. This number is not very large and does not seem to be a priority in protecting the environment. However, if you look at it from another angle, you will find that global mobile phone shipments reached 1.2 billion units last year, and each mobile phone has its own dedicated charger. Of the 1.2 billion mobile phones, an estimated 500 million are alternative mobile phones. Getting a new phone is usually exciting, but people obviously don't have any interest in replacing the charger. When you realize that the cycle of mobile phone update is 18 months on average, and most mobile phones have dedicated chargers (including the same brand of mobile phones), then there are 3 to 4 useless mobile phone chargers at home. It will be strange. In fact, the probability that the previous charger is suitable for new phones is only about 10%.
This is why we have begun to see government and institutions and well-known companies in the mobile phone industry set up special organizations to reduce this waste.
In December 2006, China’s Ministry of Information Industry issued a new standard, YD/T 1591-2006, to standardize wall chargers and connecting cables. Every new phone released in the Chinese market must be certified to meet this standard.
Another major development at the recent Mobile World Congress in Barcelona in February 2009, GSMA (including the five largest mobile phone manufacturers in the world) and 17 mobile operators agreed to provide by 2012 Universal Charging Solution (UCS) using a micro USB connector.
This action is expected to eliminate up to 51,000 tons of useless mobile phone chargers. Assuming that the production of mobile phone chargers will be reduced by 20% per year, the industry is expected to reduce greenhouse gas emissions by 1.3 to 22 million tons per year.
In addition to having a significant impact on the ecology, you don't need to carry two or three chargers when you go out on vacation with your family on weekends. You can find someone to charge your phone with a charger.
standardization
However, in order for UCS to succeed, the first requirement for handset manufacturers is their endorsement of the standard for charging batteries via USB. Version 1.0 of the Battery Charging Specification, promulgated on August 8, 2007, specifies the limits and detection mechanisms for portable devices to draw current from USB-specific chargers. The Chinese communication standard YD/T 1591-2006 also puts forward the same requirements for mobile phones released in China.
The phone needs to detect and determine whether it is a USB charger or another terminal that exchanges data (such as a computer, other mobile phones, etc.). To do this, D+ and D- are shorted in the USB charger (via a resistor RDCHGR_DAT that must be less than 200Ω). If a device is connected to the phone via the USB port, the D+ line will be driven to the VDAT_SRC voltage and the sink current will be IDAT_SRC. If a specific voltage is detected on the D-line (depending on RDCHGR_DAT and IDAT_SRC), it means that the phone is connected to the USB charger.
The above battery charging specification stipulates that the maximum output current of the charger must be 1.5A, and the maximum output voltage of the charger must be 5.25V. China's YD/T 1591-2006 specifies a charger with a maximum output current of 1.8A.
The main challenge is protection
However, the main challenge is not the well-established battery charging standard, but the quality of the USB charger. In fact, an expensive smartphone may be connected to a poor quality USB charger, such as no charge monitoring, no protection, no noise, and so on. If the mobile phone is damaged by the external charger, the user is unacceptable, and it is certain that if a certain brand of mobile phone is easily damaged by charging, the impression of the mobile phone brand will be greatly reduced.
Therefore, since handset manufacturers can no longer control the quality of wall chargers, they need to install the protection circuit directly inside the terminal. Protecting your phone is more challenging than protecting your charger for two reasons:
1. With hundreds of features integrated, the phone's PCB size is greatly reduced. The thickness of the protective device must be suitable for ultra-thin mobile phones (only 7mm thick) or flip phones.
2. The protection device must not affect the performance of the phone itself, so the leakage current must be very low.
In order to select the appropriate protection device, the handset designer must perform a risk assessment of the internal charging circuit connected to the USB port.
The first known risk is electrostatic discharge (ESD). ESD can happen at any time, whether or not the phone is charging. By touching the USB connector, the user may introduce an ESD surge voltage of up to 30kV to the USB circuit. Many designers already know that USB ports must be protected by devices capable of withstanding at least four levels of surge voltage (8kV contact discharge) in the IEC61000-4-2 standard, which is not a new risk for them. A large number of transient voltage suppressor (TVS) diodes on the market are sufficient to mitigate this risk.
However, if we don't think we can rely on the quality of the USB charger, then the second risk comes along: the phone is connected directly to the indoor power line, so it is vulnerable to any surge voltages on these lines. . This is a new factor that designers need to consider. The main sources of interference on indoor power lines are:
1. Surge voltage due to industrial events (near workshops, factories, etc.) or external high-voltage power lines (switches in the power distribution network, etc.).
2. Surge voltage due to lightning.
The most dangerous is the frequent lightning surge. Because the surge voltage caused by lightning on the transmission line is not only detected when the house that rarely occurs is directly subjected to lightning strikes. In fact, every time lightning strikes the power line or just hits the ground near the power line, it creates a boost on the (buried) ground. This wave (voltage and current) travels quickly through the power line and through the various protection devices in the central power station, even the household distribution box. Then, a residual surge voltage is transmitted directly to the power outlet plugged into the phone.
This residual surge voltage is characterized as a spike di/dt associated with the lightning strike waveform. A large number of experiments and measurements have modeled such surge currents into the following waveforms, which are defined as 8/20 μs pulses in IEC61000-4-5.
The current rise time between 10% and 90% of the current peak is specified as 8 μs, and the current must be reduced to half of the peak after 20 μs.
This overcurrent is really dangerous for electronic devices designed to operate with low voltages and low currents. A good protection device must be able to absorb this overcurrent through ground (GND) and maintain a low clamping voltage to protect the charging circuit from damage.
This surge voltage is more powerful than the ESD surge and is a more daunting challenge for designers.
In France (550,000 square kilometers), 1 million lightning strikes hit the earth every year! So this phenomenon is not an accident. Even if the probability of a lightning strike on a home is small, the probability of hitting a tree or ground within a few kilometers of a house within a year is close to 100%.
Household appliances are less susceptible to these surges, but electronic devices are easy. Appliances such as computers and televisions have been designed with the insertion of power lines in mind, so they are fully protected. Other portable devices use a dedicated charger with suitable protection or are powered by a removable battery. However, if a universal charger cannot effectively prevent such a surge voltage for cost reasons, the mobile phone can easily be damaged during charging.
The surge voltage due to industrial events or switching actions on the medium and high voltage power lines can also be modeled as 8/20μs waveforms, but the peak current will be lower. The probability of their occurrence is also very high.
The second challenge is to protect the power consumption on the device. TVS diodes that protect devices from surge voltages such as 8/20μs are everywhere, but their leakage current can be as high as 20μA. A very simple calculation shows that adding a device to the bias line will reduce standby time by about 1% for a cell with 1,000mAh and 400 hours of standby time!
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