Lithium battery protection board function

Today's mobile phone batteries are all lithium batteries. All mobile phone lithium batteries have protection boards, which are usually packaged in the battery, just in the golden finger part. What is the role of the mobile phone lithium battery protection board? The following describes the function of the lithium battery protection board.

[Lithium battery protection board] The role of mobile phone lithium battery protection board Lithium battery protection board function

Mobile phone lithium battery protection board

Battery protection board, as the name suggests, lithium battery protection board is mainly for the integrated circuit board that can be charged (generally referred to as lithium battery). The reason why lithium batteries (chargeable) need protection is determined by its own characteristics. Since the material of the lithium battery itself determines that it cannot be overcharged, over discharged, over current, short circuited, and ultrahigh temperature charge and discharge, the lithium battery lithium battery assembly will always follow a protection board with a sampling resistor and a current fuse.

Definition

The protection function of the lithium battery is usually completed by the protection circuit board and the current device such as PTC or TCO. The protection board is composed of electronic circuits. It can accurately monitor the voltage and charge and discharge of the battery at -40°C to +85°C. The current in the loop controls the continuity of the current loop in real time; the PTC or TCO prevents the battery from being damaged in a high temperature environment.

The protection board usually includes a control IC, a MOS switch, a JEPSUN precision resistor and an auxiliary device NTC, an ID memory, a PCB, and the like. The control IC controls the MOS switch to conduct under all normal conditions, so that the cell communicates with the external circuit, and when the cell voltage or the loop current exceeds the specified value, it immediately controls the MOS switch to turn off (tens of milliseconds). Protect the safety of the battery cells.

NTC is the abbreviation of Negative temperature coefficient, which means the negative temperature coefficient. When the ambient temperature rises, its resistance value decreases. It uses electric equipment or charging equipment to react in time to control internal interruption and stop charging and discharging.

The ID memory is often a single-line interface memory, and the ID is the abbreviation of Identification, that is, the meaning of identification, and stores information such as the type of battery and the date of manufacture. Can be used to trace the product and limit the application.

PTC is the abbreviation of English Positive Temperature Coefficient, which means positive temperature coefficient. In the professional, the positive temperature coefficient device is usually referred to as PTC. In the battery product, the PTC can prevent the high temperature discharge of the battery and the unsafe large current. According to the voltage, current density characteristics and application environment of the battery, the PTC has special requirements.

PTC is a very important component in battery components and has an important mission to the safety of batteries. Its performance and quality are also an important factor in the performance and quality of battery packs.

When the protection board protects a single battery core, the protection board design will be relatively simple, and the technical high point is, for example, the voltage platform problem that needs attention in the design of the power battery protection board. The power battery is often required to use a large platform voltage in use. Therefore, when designing the protection board, try to make the protection board not affect the voltage of the battery discharge. Therefore, the requirements for the control IC, precision resistors and other components will be very high. Generally, the domestic IC can meet the requirements of most products, and special imported products can be used. Current sampling resistors require JEPSUN resistors to meet high precision, low temperature coefficient, and no sense. For multi-cell protection board design, there are higher technical requirements, and products with different degrees of complexity are designed according to different needs.

Lithium battery protection board function

1, overcharge protection 2, over discharge protection 3, over current, short circuit protection

Solution for mobile phone battery boot protection (from the network):

1. Charge directly on the mobile phone with the original straight flush, and the protection circuit of the battery protection board will be automatically opened.

2. Short-circuit the positive and negative terminals of the battery, and see that there is a spark on the electrode piece. Try it several times and charge it with direct charge.

3. Find a 5V DC power, touch the positive and negative poles of the battery with positive and negative poles, try several times, and then charge with the original charger.

Principle

Battery protection board works

Lithium battery protection board has different circuits and parameters depending on the use of IC, voltage, etc. Commonly used protection ICs are 8261, DW01+, CS213, GEM5018, etc. Among them, Seiko's 8261 series has better precision, and of course the price is more expensive. The latter are all from Taiwan. The domestic secondary market basically uses DW01+ and CS213. The following is explained by DW01+ with MOS tube 8205A (8pin):

The normal working process of the lithium battery protection board is:

When the cell voltage is between 2.5V and 4.3V, the first pin and the third pin of DW01 output a high level (equal to the power supply voltage), and the second pin voltage is 0V. At this time, the voltage of the first leg and the third pin of DW01 will be respectively added to the 5th and 4th legs of 8205A, and the two electronic switches in 8205A are connected to the voltage of DW01 because of their G pole, so they are all in the on state, that is, Both electronic switches are on. At this time, the negative electrode of the battery cell and the P-end of the protection plate are equivalent to direct communication, and the protection plate has a voltage output.

Protection board over-discharge protection control principle:

When the battery is discharged through the external load, the voltage of the battery will gradually decrease, and the voltage inside the DW01 will be monitored in real time through the R1 resistor. When the cell voltage drops to about 2.3v, DW01 will consider the cell voltage has been in the state of over-discharge voltage, and immediately disconnect the output voltage of the first pin, making the voltage of the first pin change to 0V, and the switch tube in 8205A will be closed because the fifth pin has no voltage. At this time, the B- of the battery cell is disconnected from the P- of the protection board. That is, the discharge circuit of the battery cell is cut off, and the battery cell will stop discharging. The protection board is in an over discharged state and is maintained at all times. After the P and P-charge voltages of the protection board are indirectly charged, the DW01 stops the over discharge state immediately after the B-detects the charging voltage, and re-outputs the high voltage on the first pin to turn on the over discharge control tube in the 8205A. That is, the B- of the battery cell and the P- of the protection board are reconnected, and the battery core is directly charged by the charger.

Protection board over charge protection control principle:

When the battery is normally charged by the charger, as the charging time increases, the voltage of the cell will become higher and higher. When the cell voltage rises to 4.4V, the DW01 will assume that the cell voltage is in an overcharged state. Immediately disconnect the output voltage of pin 3, so that the voltage of pin 3 becomes 0V, and the switch tube in 8205A is turned off because there is no voltage on pin 4. At this time, the B- of the battery cell is disconnected from the P- of the protection board. That is, the charging circuit of the battery cell is cut off and the battery core will stop charging. The protection board is in an overcharged state and remains there. Wait until the protection board P and P- indirectly discharge the load, so although the overcharge control switch is closed, the internal diode is in the same direction as the discharge circuit, so the discharge circuit can discharge, when the voltage of the battery When it is placed below 4.3V, DW01 stops the overcharge protection state and re-outputs the high voltage on pin 3, so that the overcharge control tube in the 8205A is turned on, that is, the battery B- and the protection board P- are reconnected. The battery can perform normal charging and discharging.

Protection board short circuit protection control principle:

In the process of external discharge of the protection board, the two electronic switches in the 8205A are not completely equivalent to the two mechanical switches, but are equivalent to two resistors with small resistance, and are called the conduction internal resistance of the 8205A. The on-resistance of each switch is about 30mU03a9, which is about 60mU03a9. The voltage applied to the G-pole is actually directly controlling the on-resistance of each switch. When the G-pole voltage is greater than 1V, the guide of the switch internal resistance is small (tens of milliohms), which is equivalent to the switch closing. When the G pole voltage is less than 0.7V, the conduction internal resistance of the switching tube is very large (several MΩ), which is equivalent to the switch being disconnected. The voltage UA is the voltage generated by the conduction internal resistance and discharge current of 8205A, and the increase of the load current will definitely increase UA. Because UA0.006L×IUA is also called the tube voltage drop of 8205A, UA can simply indicate the discharge current. . When it rises to 0.2V, it is considered that the load current has reached the limit value, so the output voltage of the first pin is stopped, the voltage of the first pin is changed to 0V, the discharge control tube in the 8205A is turned off, and the discharge circuit of the battery cell is cut off, and the battery is turned off. Discharge control tube. In other words, the maximum current allowed by the DW01 is 3.3A, which achieves over current protection.

Short circuit protection control process:

Short-circuit protection is a limit form of over-current protection. The control process and principle are the same as over-current protection. Short-circuit is only equivalent to adding a small resistance (about 0Ω) between PP- to protect the load of the protection board. When the current reaches 10A or more instantaneously, the protection board immediately protects against over current.

Prospects

Due to the rapid development of power lithium batteries in recent years, whether it is production technology or material technology improvement, or price advantage, there are considerable breakthroughs, so it also lays a solid foundation for many and many strings. The era of replacing lead-acid batteries is getting closer. Regardless of whether it is an electric bicycle or a backup power source, its market share naturally begins to expand wildly. This is an undeniable fact. Then, for the safety and longevity of the battery, the effective protection of the lithium battery is naturally indispensable. At this time, the protection board is also one of the very core components in the battery pack.

In theory, the power multi-string battery protection board has not much electronic technology content, such as circuit and software processing, there are too many choices. The main reason is how to make the protection part stable, reliable, safer and more practical. Of course, the price is one of them. To really want to do it well, it is a very complicated and careful revolving work. If you want to compare the ratio of experience to technical value, the technology only accounts for 20%. Experience accounts for 80%. It is still difficult to do a good job in the power battery protection board without three or five years of experience. Of course, doing well and being able to do it is two different things. Why is there such a conclusion? This is valid. To be honest, the circuit of the protection board is not complicated. As long as it works in the battery electronics industry for a year or two, it is not difficult to design a circuit and copy a circuit. For example: a series of power batteries, he is mainly high voltage, high current, high internal resistance work (micro current), battery pack working environment, etc., which involve many years of comprehensive experience in electronics. It is big enough to understand the whole PACK, as small as a resistor, capacitor or transistor, or attention to detail when laying the board. In a word, the protection board is mainly to stabilize, reliable, and safely protect the battery pack, to ensure the normal safe use of the battery pack or to use it for a long time. Other unique technologies and functions added are clouds.

Main role

1. Voltage protection: Overcharge, over discharge, this should be changed according to the material of the battery, this seems simple, but in terms of details, there is still experience to learn.

Overcharge protection, in our previous single-cell battery protection voltage will be higher than the battery charge voltage 50~150mV. But the power battery is different. If you want to extend the battery life, your protection voltage will choose the battery's full voltage, and even lower than this voltage. For example, manganese lithium battery, you can choose 4.18V~4.2V. Because it is multi-string, the life capacity of the entire battery pack is mainly based on the battery with the lowest capacity, and the small capacity always works at high current and high voltage, so the attenuation is accelerated. The large capacity is light and light, and the natural attenuation is much slower. In order to make the small-capacity battery light and light, the overcharge protection voltage point should not be too high. This protection delay can be done 1S to prevent the influence of the pulse and thus protect.

Over-discharge protection is also related to the material of the battery. For example, manganese-lithium batteries are generally selected at 2.8V~3.0V. Try to be slightly higher than the voltage of its single battery over discharge. Because, in domestically produced batteries, after the battery voltage is lower than 3.3V, the discharge characteristics of each battery are completely different, so the battery is protected in advance. Which is a good protection for the battery life.

The general point is to try to make every battery work in light and light work, it must be a help to the battery life.

Over-discharge protection delay time, it must be changed according to the load, such as power tools, his starting current is generally above 10C, so the battery voltage will be pulled to the over-discharge voltage point in a short time protection. The battery cannot be operated at this time. This is a noteworthy place.

2. Current protection: It is mainly reflected in the working current and over current to disconnect the switch MOS to protect the battery pack or load.

The damage of the MOS tube is mainly due to the sharp rise of temperature. The heat of the MOS tube is also determined by the magnitude of the current and its internal resistance. Of course, the small current has no effect on the MOS, but the high current, this must be done some well. When passing the rated current, the small current is below 10A, we can directly drive the MOS tube with voltage. The large current must be added to drive the MOS to a large enough drive current. The following is mentioned in the MOS tube driver.

Working current, when designing, there should be no more than 0.3W of power on the MOS tube. Calculation method: I2*R/N. R is the internal resistance of MOS, and N is the number of MOS. If the power is exceeded, MOS will produce a temperature rise of more than 25 degrees, and because they are all sealed, even if there is a heat sink, the temperature will still go up when working for a long time, because he has no place to dissipate heat. Of course, the MOS tube is no problem. The problem is that his heat will affect the battery. After all, the protection board is placed with the battery.

Over current protection (maximum current), this is an essential and very critical protection parameter for the protection board. The magnitude of the protection current is closely related to the power of the MOS. Therefore, when designing, try to give the margin of MOS capability. When laying out the board, the current detection point must be selected, not only when it is connected, which requires experience. It is generally recommended to connect to the middle of the sense resistor. Also pay attention to the interference problem at the current detection terminal because its signal is susceptible to interference.

Over current protection delay, it is also necessary to make corresponding adjustments to different products. Not much to say here.

3. Short-circuit protection: Strictly speaking, he is a voltage-comparative type of protection, that is to say, it is directly shut down or driven by the comparison of voltages. Do not go through unnecessary processing.

The setting of the short-circuit delay is also critical, because in our products, the input filter capacitor is very large, charging the capacitor for the first time during contact, which is equivalent to short-circuiting the battery to charge the capacitor.

4. Temperature protection: It is generally used on smart batteries, and it is also indispensable. But often its perfection always brings about another deficiency. We mainly detect the temperature of the battery to disconnect the main switch to protect the battery itself or the load. If it is under a constant environmental condition, of course there will be no problem. Since the working environment of the battery is uncontrollable, too many complicated changes, it is not a good choice. For example, in the winter in the north, how much is it appropriate? In the southern part of the summer, how much is appropriate? It is obvious that there are too many factors that are too wide and uncontrollable. The benevolent sees benevolence, and the wise sees wisdom.

5. MOS protection: mainly MOS voltage, current and temperature. Of course, it involves the selection of MOS tubes. The withstand voltage of MOS must of course exceed the voltage of the battery pack, which is necessary. The current is said to be the temperature rise of the MOS tube body when the rated current is passed, and the temperature rise is generally not more than 25 degrees. The personal experience value is for reference only.

MOS driver, maybe someone will say, I use MOS tube with low internal resistance and high current, but why is there a very high temperature? This is the driver part of MOS tube is not done well, the driving MOS should be big enough The current, and the specific driving current, should be determined according to the input capacitance of the power MOS transistor. Therefore, the general over current and short-circuit drive can not be directly driven by the chip, it must be added. When working at high current (more than 50A), multi-stage multi-channel driving must be done to ensure that the same current is normally turned on and off at the same time of MOS. Because MOS tube has an input capacitor, the power of MOS tube and the larger the current is, the larger the input capacitor will be. Without sufficient current, complete control will not be made in a short time. Especially when the current exceeds 50A, the current design should be more refined, and the multi-stage multi-channel driving control must be achieved. Only in this way can the normal over-current and short-circuit protection of MOS be guaranteed.

MOS current balance, mainly when multiple MOS are used together, the current through which each MOS transistor passes, the opening and closing times are the same. This is to start with the drawing board. Their input and output must be symmetrical. It is necessary to ensure that the current through each tube is consistent.

6. Self-consumption power, this parameter is as small as possible, the most ideal state is zero, but it is impossible to do so. Just because everyone wants to make this parameter small, there are many people who have lower requirements and even outrageous. We think about it, there are chips on the protection board, they are working, can be done very low, but reliability? It should be to consider the problem of self-consumption when the performance is reliable and completely OK. Some friends may have entered a misunderstanding, and the self-consumption is divided into the overall self-consumption and the self-consumption of each string.

The overall power consumption, if it is between 100 and 500uA, is not a problem, because the power battery capacity itself is very large. Of course, the power tools of another analysis. For example, the 5AH battery, discharging 500uA, will last for a long time, so it is very weak for the whole battery pack.

Each string of self-consumption is the most critical, this is not possible to zero, of course, it is carried out under the condition that the performance is completely feasible, but one point, the self-consumption power of each string must be consistent, generally the difference of each string cannot be more than 5uA. At this point, everyone should know that if the power consumption of each string is different, the battery capacity will change when it is left for a long time.

7. Equilibrium: This piece of equilibrium is the focus of this article. At present, the most common methods of equalization are divided into two types, one is energy-consuming and the other is trans-power.

A energy-consuming equalization is mainly to lose excess power by using a certain amount of batteries in a series of batteries or a resistor with a high voltage. It is also divided into the following three.

First, the charging time is balanced, it is mainly when the voltage of any one battery is higher than the average voltage of all the batteries when charging, it starts to equalize, no matter what the voltage of the battery is, it is mainly applied to the intelligent software solution. Of course, how to define can be arbitrarily adjusted by software. The advantage of this solution is that it gives more time to do the voltage equalization of the battery.

Second, the voltage fixed-point equalization is to set the equilibrium start at a voltage point, such as manganese lithium battery, many of which are set at 4.2V to start equalization. This method is only performed at the end of the battery charging, so the equalization time is short, and the use can be imagined.

Third, static automatic equalization, it can also be carried out during the charging process, or it can be carried out during discharge. What is more, when the battery is in the static state, if the voltage is inconsistent, it is also balanced until the battery voltage Achieve consistency. But some people think that the battery is not working, why is the protection board still hot?

All three are balanced by reference voltage. However, high battery voltage does not necessarily mean high capacity, perhaps quite the opposite. The following will discuss.

The advantage is that the cost is low, the design is simple, and the battery voltage can play a certain role when the battery voltage is inconsistent, which is mainly reflected in the voltage inconsistency caused by the self-consumption of the battery for a long time. In theory, there is a weak feasibility.

Disadvantages, complicated circuit, many components, high temperature, poor anti-static, high failure rate.

The specific discussion is as follows.

When the new single cell is divided into partial pressure and internal resistance, the PACK will be formed. The total monomer capacity will be low, and the monomer with the lowest capacity will have the fastest rise during charging. It is also the first to reach the starting equilibrium voltage. At this time, the large-capacity monomer has not reached the voltage point and does not start to equalize, and the small capacity does start to be balanced, so that each time the cycle works, this small-capacity monomer It has been working in a full and full state, and it is also the fastest aging, and the internal resistance will naturally increase slowly compared with other monomers, thus forming a vicious circle. This is a huge drawback.

The more components are, the higher the failure rate.

Temperature, as you can imagine, energy-consuming, is to use the so-called excess electricity to consume excess electric energy in the form of heat. It has become a veritable heat source. The high temperature is a very fatal factor for the cell itself. It may cause the battery to burn and may cause the battery to explode. Originally, we were trying every means to reduce the temperature of the entire battery pack, and the energy consumption was balanced. At the same time, its temperature was so high that everyone could test it, of course, in a totally enclosed environment. In general, it is a heating element, and heat is the deadly natural enemy of the battery.

Electrostatic, when I personally designed the protective plate, I never used a low-power MOS tube, even one, because I have learned too many lessons in this field. It is the electrostatic problem of MOS tube. Not to mention the working environment of small MOS, if the workshop humidity is lower than 60% in the production and processing of PCBA patch, the defect rate of small MOS will exceed 10%, and then the humidity will be adjusted to 80%. The defect rate of small MOS is zero. You can try. What does this point to? If our product is in the northern winter, whether the small MOS can pass, it needs time to verify. Moreover, the MOS tube is only damaged by short circuit. If the short circuit is conceivable, it means that the battery will be damaged immediately. What's more, we still use a lot of small MOS on balance. At this time, some people will suddenly realize that it is no wonder that the returned goods are all due to the damage of single battery caused by the bad balance, and are all MOS broken. At this time the battery factory and the protection board factory began to quarrel. Who's to blame?

B energy transfer equalization, which is to transfer a large-capacity battery to a small-capacity battery in the form of energy storage, which sounds very smart and practical. It is also divided into capacity time equalization and capacity fixed point balance. It is balanced by detecting the capacity of the battery, but it does not seem to take into account the voltage of the battery. Think about it take 10AH battery pack as an example. If there is one capacity in the battery pack at 10.1AH, a capacity small point is at 9.8AH, the charging current is 2A, and the energy equalization current is 0.5A. At this time, 10.1AH should charge a small capacity of 9.8AH, and the charging current of 9.8AH is 2A+0.5A=2.5A. At this time, the charging current of 9.8AH battery is 2.5A, then the capacity of 9.8AH It is replenished, but what is the voltage of the 9.8AH battery? It will obviously rise faster than other batteries. If it reaches the end of charging, 9.8AH will be greatly overcharged in advance, in each charge and discharge cycle. The small-capacity battery has been in a deep-filled state. And if other batteries are full, there are too many uncertainties. The faint and intuitive analysis is small, and the analysis is too much to be confused.

Other related

If you insist on using balanced functions, I can conclude that this person does not have the experience of mass production of power battery protection boards or PACK. If there is a large-scale production, he will certainly suffer a lot of losses in the balance. Personally think that it is a bit funny to use the protection board in a balanced way. Because the protection board is protected, it only protects the battery at the most extreme time. It has no ability to improve the performance of the battery. The protection board is only a passive part. Can the protection wire or protection switch at home be improved? Electricity at home? Of course impossible. It only serves as a protection.

Batteries

The cell is the active device, and we want to improve the performance of the cell and technology, mainly consistency. Say again balanced do go up in protective board, no matter be from theory or be applied actually, it has harm advantageous, but in theory, balanced have certain effect, but use how old, apparent and visible. Why? Because charging is generally at 2~10A current, and the balance we can only do 200mA at most. This difference is too great, and some equalization schemes start at the end of the charging voltage. And it has a downside, too much.

Port

VDD is the positive pole of the IC power supply, VSS is the negative pole of the power supply, V- is the over current/short-circuit detection terminal, Dout is the discharge protection execution terminal, and Cout is the charging protection execution terminal. 2, protection board port description: B+, B- are respectively connected to the positive pole of the battery, negative: P+, P- are the positive and negative poles of the protection board output respectively; T is the temperature resistance (NTC) port, generally need to use the MCU of the appliance In conjunction with the generation of protection actions, as will be described later, this port is sometimes also labeled ID, which means the identification port. At this time, R3 is generally a fixed resistance resistor, which allows the CPU of the appliance to identify whether it is a designated battery.

1. Output negative pole, charging negative pole, battery negative pole, must be wired in order, do not reverse the circuit to avoid burning circuit components

2, Charging line, discharge line, battery negative. Try to use thick lines, otherwise it will not pass large current, it will protect against over current, causing the circuit to not work.

3. The positive output of the battery does not need to pass through the protection circuit and is directly connected to the output.

The page contains the contents of the machine translation.