Fast charging has received widespread attention as a solution to insufficient battery life.

　　Fast charging technology involves two major modules: one is the charging device, including charging head, charging cable, mobile phone integrated circuit (IC) and algorithm; the other is the battery itself. It can be said that the nature of the battery itself determines the potential for fast charging, and the quality of the charging device lies in the depth of the potential.

　　In other words, the nature of the battery itself is the "essence". If battery technology makes great progress, then the battery life problem will be solved. However, battery technology is limited by the boundaries of physics and chemistry, and it is not that simple to make progress. Therefore, major mobile phone manufacturers The fast charging technology mainly refers to innovations in charging devices.

　　Fast charging technology on the charging device side

　　Whether it is OPPO's VOOC fast charging technology or Qualcomm's QuickCharge2.0 technology, they are both fast charging technologies on the charging device side. Their essence is to increase the voltage/current reaching the battery as much as possible under certain restrictions.

　　Certain restrictions: For mobile phone batteries, the restrictions are mainly safety conditions and durability conditions. The so-called safety means that it will not explode if it is charged too fast; the durability condition means that charging it too fast will cause the lifespan to decay, but it should not decay too fast, and it can be used for at least one year.

　　Increase the voltage/current reaching the battery as much as possible: OPPO's fast charging promotion emphasizes "low voltage and high current", which will be misleading: it feels like saying that fast charging is divided into two factions, one is to increase the current, and the other is to increase the voltage. The same as pie. In fact, we can simply regard the battery as a combination of a series of resistors and capacitors. The voltage at any time is a single-valued function of the current, which has a one-to-one correspondence.

　　Two technical routes on the charging device side

　　So, is OPPO's so-called "low voltage and high current" deceiving people? Not necessarily, it is just a marketing slogan. We have all learned Joule's law, heating power = square of current * resistance. When charging quickly, heat is generated The power will be too high, and the charging cable and the interfaces at both ends of the charging cable will be unable to bear it. How can the heating power be reduced? In order to solve this problem, the technical route is divided into two groups:

　　1) Resistance reduction school: This is OPPO’s VOOC technology. The general idea is to thicken the charging cable and expand the charging cable from ordinary 4-pin or 5-pin to 7-pin. The wire is thicker, the cross-sectional area is increased, the resistance is reduced, and the heat generation is also reduced.

　　2) Current reduction school: Charging power = current * voltage. If you want to reduce the current, you need to increase the voltage. After the voltage is raised at the charging head, it is lowered again at the mobile phone's integrated circuit to charge the battery. This is consistent with the idea of our country's "UHV transmission project, which is Qualcomm's QuickCharge or MTKPEP.

　　From the perspective of voltage, compare traditional slow charging, reduced resistance fast charging technology and reduced current fast charging technology, as shown in the figure below.

　　a) In traditional slow charging technology, the charging head reduces 220V to 5V, transmits it to the voltage reduction circuit of the mobile phone through the charging cable, and reduces the voltage to 3.3V-3.6V before charging the battery.

　　b) In reduced current fast charging technology, the charging head reduces 220V to about 9-12V. The charging line has high voltage, low current, and low heat. The voltage is then reduced through the new voltage-reducing circuit of the mobile phone (such as Qualcomm's QuickCharge technology). to 3.3V-3.6V and then supply the battery.

　　c) In the resistance-reducing fast charging technology, OPPO reduces the voltage to 3.3V-3.6V in the charging head. The charging line has low voltage and high current, but due to the thickness of the line, the resistance is small and the heat is also small. In this way, the mobile phone does not need to step down again (dashed line in the picture), but can directly supply power to the battery.

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