The rise of smart phones has caused the power consumption of mobile phones to rise rapidly. The cost and battery technology have limited the battery life. When there is no way to solve the problem of battery life, it is a matter of course to solve the problem of mobile phone standby. In this context, more and more mobile phone fast charging technologies are being used and favored by mobile phone manufacturers.
One: fast charging technology principle - fast charging principleThe battery core is still lithium-ion. Most manufacturers are basically "open source" and "throttle". Battery manufacturers are striving to increase energy density and increase capacity. Chip manufacturers are looking for low-power Solutions, but Both have a ceiling: the former is limited by the portability of the phone, and the latter is a technical limitation.
Since the effect of open source and throttling is not obvious, manufacturers have begun to adopt the "curve to save the country" program: to improve the charging speed of mobile phones, from the conventional 1-2 hours to become shorter, in order to reduce the cost of charging time, in exchange for convenience.
The basic condition for battery charging is that the charger voltage is higher than the battery voltage to overcome the battery voltage and cause it to generate a charging current to complete the charge transfer process.
Junior high school physics has learned, power (P) = voltage (U) x current (I), in the case of a certain battery power, power marks the charging speed, you can shorten the charging time by the following three ways:
1, the current does not change, boost the voltage
2, the voltage is constant, increase the current
3. Both voltage and current are improved
Comparing the charging to the water storage in the pool and raising the voltage will bring more pressure on the pool wall, posing a safety hazard. Therefore, there are not many ways to simply use the boost voltage.
From the physical calculation formula, power (P) = voltage (U) x current (I), in the case of a certain battery power, the power marks the charging speed, we can shorten the charging time in the following three ways.
1. High-voltage constant current mode: The charging process of a general mobile phone is to first reduce the 220V voltage to the 5V charger voltage, and the 5V charger voltage to the 4.2V battery voltage. During the entire charging process, if the voltage is increased, heat is generated, so when charging, the charger will heat up and the phone will heat up. Moreover, the greater the power consumption, the greater the damage to the battery.
2. Low-voltage high-current mode: When the voltage is constant, the current can be increased by using a parallel circuit. Under constant voltage, the smaller the pressure shared by each circuit after parallel shunting, the other is also carried out in the mobile phone. In the same way, the pressure on each circuit is smaller.
3, high voltage and high current mode: This way increases the current and voltage at the same time, so from the previous formula P = UI, we can know that this way is the best way to increase power, but increase the voltage At the same time, more heat is generated, so that the more energy is consumed, and the voltage and current are not freely increased without limitation.
A common problem with these three approaches is the higher demand for electronic components for chargers, cell phones, and charging data lines. Qualcomm wants to take advantage of its technical advantages to make a third way, while OPPO chooses the next best and adopts the second way to improve charging efficiency.
It is more common to increase the current with constant voltage. Currently, the standard adapter of the mobile phone is usually 5V/1A output. Some manufacturers increase the charging current to 2A, which shortens the charging time of the mobile phone to a certain extent. This is indeed a solution, but it is a solution. The problem is, first of all, 2A needs both charger and mobile phone support, there are controllers on the mobile phone, not much current can support, if you use 2A charger to charge only 1A mobile phone, in fact, the output is only 1A.
In addition, the current can not be improved indefinitely. Large current charging will generate more heat. If the heating speed exceeds the heat dissipation speed and there is no protection mechanism, the temperature of the battery will rise continuously, and the life will be reduced or even explode. All electronics, chargers and the product itself limit the maximum current.
At present, two methods of increasing the charging power either increase the voltage, increase the current, or increase the voltage and current. And only certified mobile phones and adapters can achieve efficient charging.
First, the charger steps down the 220V of the household electric power to the 5V output to the Micro USB interface of the mobile phone, and then the internal circuit of the mobile phone is stepped down to about 4.3V to charge the battery. There are two steps in the buck.
Let's take a look at the charging time and charging process of the lithium battery.
In the above figure, the abscissa is time and the ordinate is the lithium battery voltage. Due to the particularity of the lithium battery, overvoltage or undervoltage will cause the battery to be scrapped. Therefore, the current lithium battery charge and discharge protection circuit principle is to measure the lithium battery voltage, and then judge whether the lithium battery is in a normal state according to the voltage (non-overvoltage, non-under Pressure).
The charging current of the lithium battery is shown in the pink line above. Lithium battery charging is divided into three stages, namely constant current pre-charging, high-current constant current charging and constant voltage charging.
When the voltage is lower than 3.0V, the charger will precharge the lithium battery with 100mA current, which is the CC Pre-charge stage in the above figure. The Chinese name is the constant current pre-charge phase, and the purpose is to slowly recover the over-discharged lithium battery. Is a protective measure. A qualified charger will have this charging phase.
Then the problem is related. When the lithium battery voltage is higher than 3.0V, it enters the second stage, the high current constant current charging phase (CC Fast charge). Since the lithium battery has been precharged in the first stage, its state has been relatively stable (the role of the precharge phase can be understood as such - but not rigorous). Therefore, in the second stage, the charging current can be appropriately increased. According to different batteries, the current can vary from 0.1C to several C. C refers to the battery capacity, such as 2600mAh lithium battery, 0.1C is Refers to the current of 260mA.
In this charging phase, the standard charging recommended by the state is to charge with 0.1C current, which is the standard charging. However, the standard charging standard was proposed very early, more than a decade ago. At that time, because lithium battery technology is far less stable than current (not allowing high current charging), so there will be such a standard ~~~ The only advantage of using standard charging is that the charging process is stable, the probability of explosion is very small; It is time! ! !
Fast charging means charging at a current of more than 0.1C at this stage. If the lithium battery capacity is 2600mAh, then the standard charging current is 260mA, as long as the charging current is greater than 260mA, it can be defined as fast charging. However, from the current level of lithium battery and the level of charge and discharge management chip, it is no problem to charge with 1C current. So fast charging is not as dangerous as you might think. Generally, the charging current for fast charging is 0.2~0.8C, so fast charging is safe. Due to the improvement in recent years, the current chargers are basically fast charging types.
The last stage of charging the lithium battery is the constant voltage charging phase. When the lithium battery voltage is equal to 4.2V, the charger enters the constant voltage charging mode. At this stage, the charging voltage is constant at 4.2V, and the charging current is coming. The smaller (slowly filled, the current must be smaller ~). When the charging current is less than 100 mA, it is judged that the battery is full and the charging circuit is cut off.
The characteristics of this stage can also explain why the phone is fully charged, pull out the USB cable and plug it in again, and the phone shows to continue charging.
In addition, it needs to be said: the above charging is the most ideal charging process for a single-cell lithium battery, and the current qualified lithium battery charging and discharging protection board works like this.
At present, the batteries used in mobile phones are all lithium-ion batteries. When the mobile phone is working, the battery is continuously discharged, the battery voltage is continuously decreased, the current discharged by the battery is different, and the curve rate of the voltage drop is also different. Generally, the battery voltage is 3.5V to 4.2. 90% of the battery energy is concentrated between V. The battery energy distribution is shown in the figure below.
Battery energy distribution overview
In combination with the actual situation of the lithium battery, the working setting of the general mobile phone is set to be unable to talk or forcibly shut down when the lithium ion battery is discharged to a certain degree. Deep discharge will cause irreversible damage to the life of lithium-ion batteries, so the shutdown voltage is generally set to about 3.5V. From the energy distribution of the battery and the actual situation of the use of the mobile phone, the charging current that affects the charging time is the charging current in the constant current charging phase. The charging current set by the mainstream mobile phone is about 450 mA. If you want to achieve fast charging, the most practical way is to increase the charging time of constant current. The best charging rate for lithium batteries is 1C, which means that a 1000 mAh battery pack needs to be quickly charged at 1000 mA. Charging at this rate can achieve the shortest charging time without reducing the performance and shortening of the battery pack. Service life. For a battery with an increasing capacity, to achieve such a satisfactory charging rate, it is inevitable to increase the charging current value.
Two: fast charging technology principle - fast charging program typical application circuit diagramThe fast charging solution consists of two parts, a charger part and a power management part. The chip of the power management part is placed in the mobile intelligent terminal, and has an independent power management chip, and some are directly integrated in the mobile phone set, and the power management chip is lithium. The entire charging process of the battery is managed and monitored, including complex processing algorithms. The lithium battery charging includes several stages: pre-charging stage, constant current charging stage, constant voltage charging stage, trickle charging stage, and charge management chip according to lithium battery. The electrical characteristics of each stage of the charging process, send a command to the charger to inform the charger to change the charging voltage and current, and the charger receives the demand from the charging management system, adjusts the output parameters of the charger in real time, and cooperates with the charging management system to achieve fast Charging.
The following figure is a typical application circuit diagram for matching MediaTek
The AW3208, introduced for the MT6235/36 platform, provides intelligent charging while adding OVP functionality to meet fast charging capabilities. As shown in Figure 2, the AW3208 has built-in proprietary K-ChargeTM technology that intelligently adjusts the output current based on the chip temperature to ensure the safety of the entire charging system during charging. This makes the mobile phone not achieve normal charging due to high ambient temperature or excessive charging current, which causes the chip to enter over-temperature protection. The figure above shows a typical application diagram on MT6235 and MT6236.
The following figure is a typical application circuit diagram of Qualcomm QC2.0
In fact, in general, the fast charging technology commonly used in mobile phones on the market basically comes from three companies: Qualcomm, MediaTek and OPPO. For example, Xiaomi 5 uses the fast charging technology of QC3.0.
1. Qualcomm Quick Charge
Let's talk about Qualcomm first. Now Qualcomm QC4.0 has been released, but most of the Qualcomm Quick Charge fast charging standards commonly available on the market are QC2.0 and QC3.0, compared to 5V/2A in the first generation. For fixed current and voltage technology, QC2.0 provides voltages of three gears of 5V, 9V and 12V, as well as currents of up to 3A (generally mobile phone adapters do not reach so much). Compared to QC1.0, the charging rate has increased a lot.
Let's take QC2.0 as an example. Quick Charge 2.0 requires both mobile phones and chargers to meet this standard. In order to prevent the old version of the phone from being burned by excessive current during charging, an IC controller is added to the charger. Of course, 5V low voltage and 1A current are also available for non-compliance with the Quick Charge standard.
Quick Charge 2.0 has been integrated into the Qualcomm Snapdragon 801 processor chip. Currently, mobile phones that support this technology can be supported with the corresponding chargers, such as Xiaomi 4, Samsung S5 or HTC One M8. In theory, Quick Charge 2.0 is 75% faster than traditional USB charging. It can charge 60% of the battery for 3300 mAh in 30 minutes.
The limitations of this technology are in the chip, which is Qualcomm's technical barrier. Although the Snapdragon 210 is also supported by this entry, non-Qualcomm chips, such as Meizu's Samsung Exynos, Huawei's HiSilicon, and MTK6595, have no choice.
In fact, QC2.0 has basically solved the problem of charging power. If the charging power is increased, it may cause serious mobile phone heating problems. Therefore, the starting point of QC3.0 is to solve the receiving efficiency of the mobile phone side.
Compared with QC2.0, Qualcomm QC3.0 mainly adds an "Intelligent NegoTIaTIon for OpTImum Voltage" (INOV) algorithm, which can be intelligently adjusted with a step of 200mV, providing flexibility from 5V to 20V. Choice (the original QC2.0 only supports three gears of 9V, 12V, 20V). In this way, the mobile phone can obtain the right voltage at different charging stages to achieve the expected charging current, so that the power loss is minimized.
Qualcomm officially announced that QC3.0 charging efficiency is 1 times higher than QC1.0, 38% higher than QC2.0, 4 times that of ordinary charging technology, and can charge a typical mobile phone from zero in about 35 minutes. Charge to 80%!
2, OPPO VOOC flash charge
Domestic manufacturer OPPO has developed a VOOC flash charging solution. The principle is to increase the current by constant voltage, but this method has been improved. Their method is to increase the current to 4.5A by constant voltage and high current. Boost.
The charging process of the conventional mobile phone is that the adapter steps down the 220V AC to 5V DC, and the battery is charged to the battery by the charging control circuit to 4.2V. In the voltage regulation process, the power is generated due to the loss of power (this is also our It is often said that the phone will heat up when charging.) VOOC flash charging technology transplants the charging control circuit to the charger, transplants the heat source to the adapter, and transfers the heat problem of the mobile phone.
The VOOC flash charger also has a special chip called MCU chip, which replaces the charging control circuit in traditional charging. This chip can automatically identify whether the current charging device supports VOOC flash charging. In addition, its charging port, although also MicroUSB, has 7 pins, the battery is also specially made, and the contacts reach 8.
Special adapters, batteries, data lines, circuits, interfaces, all of which are sufficient to enable flash charging and achieve a 4.5A high current output input. If it is detected that it is not supported, it will automatically use the stable charging current to achieve slow charging.
OPPO VOOC flash charging comparison 1A and 2A current charging speed
3, MediaTek fast charging technology - Pump Express
MediaTek also launched its own fast charging technology - Pump Express, and with OPPO bar, MediaTek Pump Express 3.0 fast charging technology, a mobile phone power from 0 to 70% only 20 minutes, is expected to officially at the end of this year application. Known as charging for 5 minutes for 4 hours, OPPO's announcement is overwhelming, but it is only charging for 5 minutes for 2 hours.
MediaTek Pump Express features: Allows the charger to determine the initial voltage required for charging according to the current. The pulse current command sent by the PMIC is transmitted to the charger via the USB Vbus. The charger adjusts the output voltage according to this command, and the voltage gradually increases up to 5V. Maximum charging current.
MediaTek currently has two fast charge specifications:
(1) Pump Express provides less than 10W (5V) output power for fast DC charger, controlled output voltage: 5V/4.8V/4.6V/4.4V/4.2V/4.0V/3.8V/3.6V, mainstream output Power: 5V/1A & 5V/1.5A
(2) Pump Express Plus provides the charger with an output power greater than 15W. The difference is that the controlled output voltage is increased by 12V, 9V and 7V, which is 12V/9V/7V/5V/4.8V/4.6V/ 4.4V/4.2V/4.0V/3.8V/3.6V.
The principle of MediaTek MTP Pump Express Plus is similar to that of Qualcomm Quick Charge. Based on the guaranteed charging current of 2A, the charging power is increased by increasing the voltage of the charger to the USB port of the mobile phone.
4, TI MaxCharge
TI's MaxCharge fast charging technology integrates a 5A single-cell Li-Ion battery charger circuit that supports input voltages up to 14V at currents up to 5A. Backward compatible with Qualcomm Quick Charge 2.0's 9V, 12V two-speed voltage, the MediaTek Pump Express Plus's 7V, 9V, 12V support is also a problem. Compared to existing battery chargers, this device reduces charging time by more than half and increases charging time by up to 60%.
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