Times are changing, and the power consumption of large-screen smart phones has reached a new level. People's dependence on mobile phones is far more than 10 years ago. Nowadays, mobile phones have become a tool for people to communicate with the world (including but not limited to surfing the Internet and talking), and to communicate with themselves (including games, etc.). The ratio of time actually used by mobile phones has greatly increased. This places extremely high requirements on the energy of mobile phone batteries. At the same time, the design of mobile phones tends to be thin and light, and does not support rapid battery replacement. Energy input is completely dependent on charging and data ports.

　　However, instead of increasing the size of the mobile phone’s charging port, it is moving in the direction of continuous miniaturization. The decrease in the electrical contact area of the port is followed by an increase in contact resistance and a decrease in heat dissipation capacity, which reduces the current that the port can pass.

　　The input power of the port = input voltage x input current. It can be seen that the contradiction between the reduction of port current capacity and the increase of port input power can be solved by increasing the port input voltage. This is the original intention of Qualcomm QC2.0/3.0HVDCP (high voltage dedicated charging port). It is worth mentioning that USB3.1PD and MTKPUMPEXPRESSPLUS also use the same solution.

　　principle analysis

　　Before talking about the hardware implementation of QC fast charging, I would like to mention the comments on QC fast charging that I saw on the Internet some time ago. Many articles have said that the high-voltage charging used by QC is harmful to mobile phone batteries. In my opinion, the existence of this statement is precisely caused by the lack of understanding of how the circuit in the mobile phone completes the battery charging process. Therefore, the following part not only introduces how QC is implemented by hardware, but also introduces how other mobile phones complete battery charging.

　　The battery charging circuit in the mobile phone can be divided into two parts according to the function (but it does not mean that the two parts are physically separated, in fact, the two circuits are often implemented in the same integrated circuit).

　　1, measurement-feedback control part

　　is responsible for monitoring the key parameters of battery charging (such as battery charging current, battery current voltage, battery temperature), adjusting parameters such as charging current, or shutting down charging according to preset battery charging algorithms. The measurement and feedback control part of the mobile phone charging circuit can usually adjust certain parameters through software programming. Even some mobile phone charging measurement, feedback control part of most functions are completed by software. Most mobile phone charging control algorithms for lithium batteries are based on constant current-constant voltage process or its variants. The process of constant current and constant voltage charging is generally like this. First, when the battery is lower than its charging limit voltage (in the past, mobile phones were 4.2v, now common 4.35V, occasionally 4.40V), the battery is charged with a constant current.

　　The ratio of the size of the constant current to the battery capacity (called the charging current rate) is closely related to the charging speed of the mobile phone battery. To increase the charging speed of mobile phones, increasing the charging current rate is an effective means. However, the mobile phone battery has a limited ability to accept the charging current rate. Excessive charging current rate will increase the cycle attenuation of the mobile phone battery, and may even cause battery safety issues. At present, most mobile phone batteries can accept a charging current rate of 0.5-1 times. For example, for a 3000mAh cell phone battery, a charging current rate of 0.5-1 times corresponds to a charging current of 1500mA-3000mA. By optimizing the battery structure and formula, the battery can accept a greater charging current rate. As far as the current situation is concerned, the upper limit of the charging current rate of the mobile phone battery is usually not the bottleneck of the charging speed of the mobile phone.

　　When the battery reaches the battery's charge limit voltage through constant current charging, the charge limit voltage is maintained by gradually reducing the charge current. Because the lithium-ion battery voltage increases with the increase of battery fullness, the greater the charging current, the higher the battery voltage, so when the fullness continues to increase, reducing the charging current can keep the battery voltage constant. This is Constant pressure process. When the charging current is reduced to a predetermined value, the charging current will be turned off, and the charging will be completed.

　　2, voltage and current conversion part

　　The function of this part of the circuit is to convert the electric energy obtained from the charging port of the mobile phone into the charging current of the battery under the control of the measurement and feedback control part. Since the input voltage of the mobile phone charging port is usually 5V, 9V, and the like, which does not match the battery voltage (3.0V-4.35V, which varies with power and charging current), it needs to be changed. It is precisely because of this conversion process that the claim that high-voltage charging affects battery life is very absurd. Because the charging voltage and current of the mobile phone battery are determined by the charging program preset by the measurement and feedback control part. If the input voltage is a little higher or lower, as long as it is within the allowable range of the voltage-current conversion part, it will be converted by the voltage-current conversion part to the value set by the program.