Issues that should be considered in charging technology
First: Battery acceptance
To put it simply, charging is about feeding the battery. So first of all, we have to consider the battery’s feelings. Taking the popular iPhone X Plus, Huawei P9, Le 2, and Xiaomi Note as examples, the battery capacity does not exceed 3000mAH. According to 4.35V as the highest voltage and 1.5C charging, the maximum possible charging power is about 20W. Of course, this is the limit. In addition to power receiving capacity, current acceptance is also involved. When charging at 1.5C, the charging current of a 3000mAH battery will reach 4.5A. Therefore, the battery contacts and the current transmission structure inside the battery cell must be optimized as necessary.
Second: Power supply capacity of the adapter
Without considering the interface’s bearing capacity, 20W power is easy for the adapter. However, the maximum current carrying capacity of the traditional MicroUSB interface in the standard specification is 2A and the maximum voltage is 5.25V. There is only 10.5W, which cannot meet the 20W requirement. How to solve this problem? Obviously there are two solutions, increasing the current or increasing the voltage. If the physical interface is not changed, increasing the current is not an option, so increasing the voltage is the only option in the MicroUSB era, which is the origin of Qualcomm’s QC fast charging method. Therefore, we can see that 1.5A is the current recommended by the QC standard, because 2A is the limit of MicroUSB. The general consensus in the industry is not to use the device to the limit value, but to reserve a margin. In this regard, OPPO and Qualcomm took the opposite path. They physically patched MicroUSB and added additional contact pins specifically for transmitting large currents. The maximum charging current reached 4.5A, but the voltage remained unchanged at 5V. It also achieved a power transmission of more than 20W. The emergence of the Type-C interface has made this problem no longer exist, because the TYPE-C port supports a maximum input current of 5A, which can fully meet the fast charging needs of existing mobile phone batteries.
Third: Charging management and heat dissipation capabilities of mobile phones
Charging management and heat dissipation capabilities of mobile phones. Charging management inevitably involves voltage conversion, constant current control and other links, which will lead to a decrease in charging efficiency and heat dissipation problems. Therefore, the best charging design in theory is that the mobile phone does not manage charging internally, and completely hands it over to the external charger for control. In this regard, QC is at a disadvantage, because high voltage and low current input will inevitably lead to energy conversion inside the mobile phone, turning it into low voltage and high current. This will bring big problems in the heat dissipation of the mobile phone. Therefore, from a technical point of view, the historical limitations of QC have been highlighted. The more serious problem is that the TYPE-C interface and USB PD are strictly prohibited from adjusting the charging voltage by methods other than USB PD. Qualcomm has made great efforts to persuade the USB-IF organization to allow QC and PD to coexist in the TYPE-C interface. However, unfortunately, it was ruthlessly rejected, and the latest TYPE-C1.2 and USB PD3.0 maintained the description of this feature. Therefore, QC will face the danger of being eliminated both technically and theoretically. Of course, Qualcomm itself is very clear about this trend. Therefore, the negotiation function of USB PD has been integrated into the latest processor core.
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