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Charger Solution
In recent years, in our country and even in the world, electronic products continue to enter our vision like green bamboo shoots after spring rain. The most intuitive ones are mobile phones, MP3, MP4, netbooks, digital cameras, electric vehicles and other electronic products. The emergence of these high-tech products has greatly promoted economic development and improved our quality of life. However, at the same time, many accidents have been caused. For example, we often hear that mobile phones explode, the battery is pregnant, and the battery is hot. Carry out reasonable protection and normal charging and discharging. In order to avoid similar tragedies from happening again, we can help from the charger. Therefore, this paper proposes an intelligent and highly concentrated multi-function charger.
1. The analysis principle of common batteries
Let's take the most common lithium polymer battery as an example. Of course, this principle is applicable to some other batteries. Our daily mobile phone batteries, digital camera batteries, MP3, MP4, etc. all use lithium polymer batteries. Lithium batteries used in daily life are basically single-core, while those used in industries or laboratories with higher requirements are basically It is a multi-cell lithium battery. The so-called multi-cell battery is to connect batteries with the same capacity, consistent internal resistance, and consistent discharge capacity in series, parallel or series-parallel. The main purpose of series connection is to increase the voltage of the battery.
We can clearly see that the higher the voltage used by the electrical appliance, the smaller the current flowing through the electrical appliance. Generally, the voltage of a single-cell lithium battery is 3.7V. If 6 sets of batteries are connected in series, the current passing through the electrical appliance will be 6 times smaller when used on the same electrical appliance. We can know that the loss of the line will be reduced by 36 times. The current without series connection is 5A, and the loss on the line will be 25 R; after series connection, the current is (5/6)A. The loss on the line is (25/36)R, from which we can know that the purpose of doing so will reduce the huge loss of capacity. Discharging with a small current can prolong the service life of the battery, because the activation factor inside the battery decreases when the battery is charging and discharging, especially when working with a large current, and the chemical reaction inside the battery increases the internal resistance of the battery. The parameters of the battery are generally 6000mah 25C. The 6000mah here means that the battery can be continuously discharged with a current of 6A for 1 hour. If it is discharged with a current of 12A, it can be discharged for 30 minutes. It can be calculated in the same way, that is to say, the smaller the discharge current is, the longer the discharge time will be. The 25C here means that the maximum discharge current of this battery is 6000*25/1000=150A.
2. Cell structure and principle
To sum up, we know that we use batteries in series or parallel in many occasions. The design of the smart charger appeared logically, because multiple batteries need centralized and unified management when charging and discharging to ensure the maximum service life of the battery. At present, the chargers we use basically charge directly in series, that is, only monitor the total voltage during charging, and stop charging the battery if the monitored voltage of the rechargeable battery reaches the standard voltage. In such a developed industrial society, the vast majority of products are produced on the production line, so there will be a phenomenon that the internal resistance of each cell is inconsistent.
When using the battery to discharge, the chemical reaction inside the battery cell is basically the same, but the intensity of the reaction may be different. Let's take the example of 6 sets of batteries connected in series, that is, 6s batteries. Since the batteries are connected in series, the current passing through each battery cell is the same during use. According to Ohm's law, we can know. However, since the internal resistance of each cell is different, the energy stones consumed by the internal resistance of the battery are different, and the voltage of each cell will be different after the discharge is completed. It is possible that the voltage of some batteries is 3.7, 3.8, 3.6, etc. If this happens, this phenomenon will occur when using this series charger. When the total voltage is 25.2V, some batteries may be overcharged, and Some batteries are in a non-saturated state. For an overcharged cell, it will seriously shorten the life of the battery. For an unsaturated cell: it will absorb the power of other cells during use, which is not conducive to the use of the battery.
3. Design principle of smart charger
The design of traditional chargers can no longer meet the needs of users, and overcharging the battery may cause the battery to explode. In order to enjoy the fun brought by technology more safely and comfortably, we specialize in this smart charger. The charging method used by this charger is no longer a serial charging method but a parallel method, and an independent balancing process is added while designing. The principle of the smart charger is as follows: the main control chip we use is ATM EG A 128 type AVR single-chip microcomputer. High security and strong confidentiality. A voltage loop circuit is mainly designed in the charger. The voltage loop circuit mainly detects whether the voltage of the battery cell is equal to the standard set voltage. If it is consistent with the set voltage, a linear small current is slowly fed into the battery. Make it able to save better quality electric energy; the other is the current loop circuit, which also needs to put O. The 05 ohm resistor is amplified by the operational amplifier and then sent to AD conversion. Finally, the pulse width of 32K hz can be controlled to control the current. If the monitored current is 50m a, the circuit can be automatically disconnected and the buzzer will start The device alarm prompts the user that the battery is fully charged.
At the same time, the charger also has 6 A-D conversion ports, which can monitor the voltage of the 6 batteries in real time by using these 6 A-D conversions. During the charging process, if the internal resistance of some batteries is small, it will show The current voltage is higher than the voltage of other batteries. Under the same circumstances, the charging time of a cell with a large internal resistance will be faster than that of other cells. This is the concept of parallel charging, that is, the charging of each cell is synchronized, but the charging between each cell will not interfere with each other. That is to say, if the charging circuit of the first battery cell reaches 4.2V, it will automatically disconnect the charging circuit of the battery cell, and the battery cell that does not reach 4.2 V will continue to charge, so that the battery can be charged to the maximum. Ability to protect the battery cell. According to the analysis of major data, the internal activation factor of lithium battery is the lowest in the low temperature environment between 3.8-3.9V, which means that if the user does not use the battery for a long time, it is best to be able to replace the battery. For this reason, the voltage is within this range and it is guaranteed to be in a low temperature environment. The charger can directly start the internal fan to achieve this uniform discharge effect and keep the voltage of each cell consistent. After the discharge is completed, the circuit will be automatically disconnected and the user will be notified by a buzzer alarm, after which the user can enter the cold storage protection.
4. Smart Charger Solution Design
The design of smart chargers based on single-chip microcomputer control needs to consider the actual functionality of each component and the compatibility after matching. Therefore, when designing, it is necessary to clarify the actual functions of each part of the components, and then apply them in combination.
The circuit of the smart charger is mainly composed of three parts, namely: (1) power circuit. (2) Main control circuit. (3) Signal controller.
Among them, the power circuit can provide stable 12V charging voltage and 14V charging voltage, as well as different voltages required by the battery during charging. The main control circuit can effectively control the charging state, for example, effectively control the charging process. Signal control can effectively guarantee charging safety.
5. Charging control technology
1. Timing charging control
This type of control method is very simple, and the main practical scope is the constant current point charging method. The constant current charging method is adopted, and the charging time required for the current is determined according to the charging condition of the battery and the specific capacity. During the specific charging process, the timer can send out a signal to allow the charger to stop charging quickly, or it can transfer the charger to keep it in the maintenance state of floating charge, so as to avoid large changes in the charging time of the battery. Current charging for a long time. Disadvantages of regular charging: It is difficult to know the capacity of the battery before charging, so the long-term operation of the battery during the charging process will cause serious heating, which can damage the battery power, and it is difficult to determine the charging time of the battery. When the charging time of the battery cannot be adjusted according to the battery status, the battery in the battery pack will be undercharged, and even many batteries will be overcharged, so this charging method can only be used when the charging power is lower than 0.3 C constant current charging.
2. Battery voltage control
(1) Maximum voltage control method: It can be known from the curve of charging characteristics that when the battery voltage reaches the maximum value, the battery can be fully charged, and it is necessary to stop charging quickly at this moment. The disadvantage of applying this method is that when the battery is fully charged, as the voltage environment increases, the temperature will also increase, and the charging rate will also increase. It will be difficult to judge whether the battery is fully charged by applying this method.
(2) Negative voltage increment: The negative increment of battery voltage has little relationship with the absolute voltage of the battery pack. This method can accurately determine whether the battery is charged without being affected by factors such as the environment and stability. Finish. But the disadvantage is that before the battery is fully charged, there will be a partial voltage drop, causing the battery to stop fast charging after detecting a negative voltage increase before it is fully charged.
6. The working principle and design of the control circuit
The negative feedback control system is mainly based on the control of the switching power supply, and the design of the main control link is very important. This paper mainly controls the charging system of its power battery. The specific control methods are three control methods: inner loop control, voltage outer loop control and double closed loop control.
When the power device is turned on and off, the main circuit is affected by different circuit topologies and exists as a nonlinear system. In the process of engineering design, it is necessary to obtain the low-frequency equivalent circuit model according to the average method of the state space, and then design the regulator according to the existing performance indicators on this basis. When designing and designing, in order to obtain better dynamic and static effects of the converter, it is more customary to use different forms of voltage or current for negative feedback.
1. Main control circuit
The main control circuit consists of four major parts: (1) current control return. (2) Charging current and capacity display circuit. (3) Detection and sampling circuit. (4) Alarm circuit.
Due to various factors in the circuit, the switching power supply is very prone to failure. Therefore, it is necessary to carefully consider when selecting the model and type of the switch, and choose according to the actual situation of the circuit.
2. Transformer
When selecting a transformer, a high-frequency transformer must be used. The performance of this transformer is relatively good, but it has higher requirements for the use of magnetic materials. The transformer can give the circuit a stable voltage output, so that the circuit can reduce the voltage impact when it is working.
3. Capacitor
Due to the problem of different frequency of use of the power supply, for the power supply used at high frequency, the loss of ordinary capacitors is quite large, and the inductance also increases accordingly. As the frequency continues to increase, the attenuation phenomenon is very obvious, which cannot meet the normal use requirements. Therefore, when selecting a capacitor, it is necessary to decide whether to use a special capacitor according to the actual situation of the circuit to meet the requirements of high frequency and high temperature resistance, so that the circuit can run stably.
4. Microcontroller
When the system is powered on, the microcontroller will detect the power supply and charger. When the power supply and the charger are both working normally, the microcontroller will feed back the detection samples to the internal system, and finally decide which charging method to use, which has met the charging requirements. The PWM pulse width can effectively control the whole process of charging, so that trickle current, high current, overcharge and floating charge are all under control. During multi-detection, it is found that the voltage of the battery is higher than the specified voltage set in the microcontroller, or the temperature exceeds the preset temperature, then the floating charge state will be turned on, and an alarm will be issued at the same time.
Summarize
The intelligent charger controlled by a single-chip microcomputer can effectively carry out charging work, and can effectively ensure charging safety at the same time. The smart charger mainly follows the design concept of safety first, efficiency first, and optimized structure. It refers to and consulted the design methods of various chargers and re-established the design scheme. The charger has been tested many times in the laboratory and has been shown to meet the conditions of use of batteries other than lithium batteries. It is believed that it can bring different enjoyment to the society and benefit the society at the same time.
The above are the details of the charger solution introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have the electronic function development needs of the charger, you can rest assured to entrust it to us. We have rich experience in customizing the development of electronic products. We can evaluate the development cycle and IC price as soon as possible, and can also calculate the PCBA quotation. We are a number of chip agents at home and abroad: Songhan, Yingguang, Jieli, Ankai, Quanzhi, realtek, with MCU, voice IC, Bluetooth IC and module, wifi module. Our development capabilities cover PCB design, single-chip microcomputer development, Bluetooth technology development, software customization development, APP customization development, WeChat official account development and other hardware and software design. It can also undertake the research and development of smart electronic products, the design of household appliances, the development of beauty equipment, the development of Internet of Things applications, the design of smart home solutions, the development of TWS earphones, the development of Bluetooth earphone speakers, the development of children's toys, and the development of electronic education products.
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