With the development of the economy, electronic products have entered the homes of ordinary people. People’s demand for the use of electronic products is also getting higher and higher. With the higher and higher demand for the use of electronic products, people’s demand for lithium batteries is also higher and higher. As a battery with relatively large electric storage, lithium batteries are used Used in various electronic products. However, some unscrupulous merchants in the market have aimed at this point. They flooded the entire market with a large number of fake and inferior batteries, making it difficult for consumers to buy genuine products.

These counterfeit and shoddy lithium batteries have serious quality problems. These counterfeit and shoddy lithium batteries are likely to have overcharge and overdischarge problems, which may cause an explosion, or a short circuit of the internal circuit may cause an explosion. However, there is a product that can effectively prevent lithium batteries from overcharging, overdischarging and short-circuiting of internal circuits. It is a lithium battery protection board. Today, I will explain the role of lithium battery protection board from a professional perspective.

We all know that the lithium battery we use is actually composed of several small internal lithium batteries connected in parallel. There are several plastic-like plates separating them in the gaps between the internal lithium batteries. These small plastic-like boards are actually lithium battery protection boards. In fact, the lithium battery protection board is not made of plastic. It is composed of several non-conductive fiberboards wrapped with a layer of oil. We all know that oil is non-conductive, which is why the lithium battery protection board can isolate several lithium batteries and avoid short circuits in the circuit.

Secondly, we talked about the lithium battery protection board also has the function of protecting the battery and avoiding battery overcharging. When the external power supply continues to quickly charge the battery, the lithium battery protection board will have a protective effect. When the internal power of the lithium battery reaches the saturation level, the internal circuit of the lithium battery protection board will automatically cut off the external fast charging power supply. So that the external power source cannot enter the battery. This is exactly the principle that the lithium battery protection board protects the battery from overcharging.

We also went to the lithium battery protection board to protect the lithium battery and prevent the lithium battery from over-discharging. When the lithium battery is over-discharged, the internal memory content of the lithium battery will undergo a qualitative change. At this time, the lithium battery protection board can sense this, so as to quickly cut off the discharge power supply so that the lithium battery will not discharge all the electricity. This ensures the stability of the internal current of the lithium battery and avoids the over-discharge of the lithium battery.

Battery protection board, as the name implies, lithium battery protection board is mainly an integrated circuit board for rechargeable (generally referred to as lithium battery) protection. The reason why lithium battery (rechargeable type) needs protection is determined by its own characteristics. Since the material of the lithium battery itself determines that it cannot be overcharged, overdischarged, overcurrent, short-circuited, and ultra-high temperature charging and discharging, the lithium battery components of the lithium battery will always appear with a protection board with a sampling resistor and a current fuse.

The protection function of lithium battery is usually completed by the protection circuit board and current devices such as PTC or TCO. The protection board is composed of electronic circuits, which can accurately monitor the voltage and charge and discharge of the cell at all times in the environment of -40℃ to +85℃ The current of the loop can instantly control the on and off of the current loop; PTC or TCO can prevent severe damage to the battery in a high temperature environment.

The protection board usually includes control IC, MOS switch, JEPSUN precision resistor and auxiliary device NTC, ID memory, PCB and so on. Among them, the control IC controls the MOS switch to turn on under all normal conditions to make the cell communicate with the external circuit. When the cell voltage or loop current exceeds the specified value, it immediately controls the MOS switch to turn off (tens of milliseconds). Protect the safety of batteries.

NTC is the abbreviation of Negativetemperaturecoefficient, which means negative temperature coefficient. When the ambient temperature rises, its resistance decreases. The electrical equipment or charging equipment is used to respond in time and control internal interruptions to stop charging and discharging.

ID memory is often a single-wire interface memory. ID is the abbreviation of Identification, which means identification, and stores information such as battery type and production date. Can play a role in product traceability and application restrictions.

PTC is the abbreviation of PositiveTemperatureCoefficient in English, which means positive temperature coefficient. Professionals usually refer to positive temperature coefficient devices as PTC for short. In battery products, PTC can prevent the occurrence of high-temperature battery discharge and unsafe high current. According to the battery's voltage, current density characteristics and application environment, PTC has special requirements.

PTC is a very important component in battery assembly products, and it bears an important mission for battery safety. Its performance and quality are also an important factor of battery pack performance and quality.

When the protection board protects a single battery cell, the protection board design will be relatively simple, and the technicality is higher, such as the voltage platform problem that needs to be paid attention to in the design of the power battery protection board. The power battery often requires a large platform voltage during use. Therefore, when designing the protection board, try to ensure that the protection board does not affect the voltage of the battery discharge, so that the requirements for control ICs, precision resistors and other components will be very high. Generally, domestic ICs can meet the requirements of most products, and imported products can be used in special cases. Current sampling resistors need to use JEPSUN resistors to meet the requirements of high precision, low temperature coefficient, and no inductance. For the design of multi-cell protection boards, there are higher technical requirements, and products with different levels of complexity are designed according to different needs.

Main technical functions:

1. Overcharge protection 2. Over discharge protection 3. Over current and short circuit protection

The solution after the mobile phone battery protection is activated (from the network):

1. Charge the phone directly with the original direct charge, which will automatically open the protection circuit of the battery protection board.

2. Instantly short-circuit the positive and negative poles of the battery, and you can see sparks on the electrodes. Try a few more times, and then use direct charging.

3. Find a 5V direct current, lightly touch the positive and negative poles of the battery with the positive and negative poles, try several times, and then use the original charger to charge.

Working principle of battery protection board

Lithium battery protection boards have different circuits and parameters according to different ICs and voltages used. Commonly used protection ICs are 8261, DW01+, CS213, GEM5018, etc. Among them, Seiko's 8261 series have better accuracy and of course the price is more expensive. The latter are all made in Taiwan. The domestic secondary market basically uses DW01+ and CS213. The following is an explanation with 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 both output high level (equal to the supply voltage), and the second pin voltage is 0V. At this time, the voltage of pin 1 and pin 3 of DW01 will be applied to pins 5 and 4 of 8205A respectively. The two electronic switches in 8205A are in the conducting state because their G poles are connected to the voltage from DW01, that is Both electronic switches are in the open state. At this time, the negative pole of the battery is directly connected to the P- terminal of the protection board, and the protection board has a voltage output.

Protection board over-discharge protection control principle:

When the cell is discharged through an external load, the voltage of the cell will slowly decrease, and at the same time, DW01 will monitor the cell voltage in real time through the R1 resistor. When the cell voltage drops to about 2.3V, DW01 will consider that the cell voltage has been In the over-discharge voltage state, immediately disconnect the output voltage of the first pin, so that the voltage of the first pin becomes 0V, and the switch tube in the 8205A is closed because there is no voltage on the fifth pin. At this time, the B- of the battery cell and the P- of the protection board are in a disconnected state. 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-discharge state and has been maintained. After the P and P- of the protection board have indirect charging voltages, DW01 will immediately stop the over-discharge state after B- detects the charging voltage, and output a high voltage at pin 1 again 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 is directly charged by the charger.

Protection board overcharge 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, DW01 will consider the cell voltage to be in an overcharge voltage state. It immediately disconnects the output voltage of the third pin, so that the voltage of the third pin becomes 0V, and the switch tube in the 8205A is closed because the fourth pin has no voltage. At this time, the B- of the battery cell and the P- of the protection board are in a disconnected state. That is, the charging circuit of the battery cell is cut off, and the battery cell will stop charging. The protection board is in an overcharged state and has been maintained. After the P and P- of the protection board discharge the load indirectly, although the overcharge control switch is turned off, the forward direction of the diode inside is the same as the direction of the discharge circuit, so the discharge circuit can be discharged. When the voltage of the battery cell When it is placed below 4.3V, DW01 stops the overcharge protection state and outputs a high voltage at pin 3 again, so that the overcharge control tube in 8205A is turned on, that is, the B- of the battery and the protection board P- are reconnected , The battery cell can be charged and discharged normally.

Principle of short-circuit protection control of protection board:

As shown in the figure, in the process of external discharge of the protection board, the two electronic switches in the 8205A are not completely equivalent to two mechanical switches, but are equivalent to two resistors with very small resistance, and are called 8205A. Turn-on internal resistance, the turn-on internal resistance of each switch is about 30m\U03a9 and a total of about 60m\U03a9. The voltage applied to the G pole actually directly controls the on-resistance of each switch. When the G pole When the voltage is greater than 1V, the internal resistance of the switch tube is very small (tens of milliohms), which is equivalent to the switch being closed. When the voltage of the G pole is less than 0.7V, the internal resistance of the switch tube is very large (several MΩ). Equivalent to switch off. The voltage UA is the voltage generated by the internal resistance of 8205A and the discharge current. When the load current increases, UA will inevitably increase. Because UA0.006L×IUA is also called the tube voltage drop of 8205A, UA can be abbreviated to indicate the size of 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 pin 1 is stopped, so that the voltage of pin 1 becomes 0V, the discharge control tube in 8205A is closed, and the discharge circuit of the battery is cut off. Discharge control tube. In other words, the maximum allowable output current of DW01 is 3.3A, which realizes over-current protection.

Short circuit protection control process:

Short-circuit protection is a limit form of over-current protection. Its 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 board. When the current reaches more than 10A instantaneously, the protection board immediately performs over-current protection.

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