Background and significance of 12V lithium battery protection circuit

Low power 12 v lithium battery premise of protecting circuit background and significance

Due to the 12 v lithium battery energy density is high, in the condition of overcharge, the battery temperature rise after the excess energy will then the electrolyte decomposition and produce gas, easy to make the internal pressure rise and the risk of spontaneous combustion or broken;On the other hand, in the condition of excessive discharge, caused by decomposition of electrolyte battery degradation characteristics and durability, reduce the number of rechargeable, shorten the battery life.So for the 12 v lithium battery of protection is very important, the 12 v lithium battery applications must have the battery protection chip, to prevent the battery overcharge, overdischarge and overcurrent.

Due to the lithium battery energy density is high, in the condition of excessive charging, the battery temperature rise after the excess energy will then the electrolyte decomposition and produce gas, easy to make the internal pressure rise and risk of spontaneous combustion or broken;On the other hand, in the condition of excessive discharge, caused by decomposition of electrolyte battery degradation characteristics and durability, reduce the number of rechargeable, shorten the battery life.Therefore is very important for the protection of lithium battery, lithium battery applications must have the battery protection chip, to prevent the battery overcharge, overdischarge and overcurrent.

To sum up, lithium battery protection circuit design is very important. But lithium battery protection circuit will increase the extra battery energy loss, reduces the cast time of battery application, which requires the lithium battery protection circuit to achieve low power consumption in high precision. A lithium battery protection chip can be done in addition to charging protection, over discharge protection and over current protection and other basic functions, but also meet the following requirements - this is also the goal of this paper designed the chip.

(1) low power consumption. Lithium battery protection circuit on the job, its power consumption is the wastage of the battery. Therefore, we should put the lithium battery protection circuit of the power consumption to a minimum.

(2) high precision detecting voltage. In order to make the lithium battery protection circuit for different working state of the battery to make the right response, protection circuit must be able to accurately measure had charge voltage protection, over discharge protection voltage parameters such as voltage.

(3) work properly under large voltage range. Due to the lithium battery protection circuit of power supply voltage of the battery voltage, the battery voltage is floating in a larger scope, reason for lithium battery protection circuit in the voltage range can work correctly.

Lithium battery protection circuit

Currently used in all kinds of batteries, lithium batteries (also known as lithium ion secondary battery or lithium ion battery) is developed in recent years a new type of power supply. Lithium battery is different from the general chemical power source, and its working process is through the charging and discharging lithium ion battery is negative in the embedded embedding and take off. Lithium battery anode carbon materials, such as graphite. The anode is lithium transition metal oxides, such as lithium cobalt oxide (LiC002).And lithium-ion battery anode materials are all use lithium ion free embedded in and out of the lithium ion embedded with layered structure compounds, lithium ion in the interlayer, in the proper electrolyte, electrochemical reaction will happen. When charging, the external electric field under the drive of lithium ion emerge from the positive lattice, through the electrolyte, embedded in the cathode in the lattice. Discharge process is just the opposite, lithium ion returned to the anode, the electrons pass along an external circuit is to reach the positive with lithium ion compound.

Compared with the common nickel cadmium, nickel metal hydride batteries, lithium batteries has many superior characteristics, mainly manifested in the following aspects:

(1) lithium battery power supply voltage is high, the general is 3.6 v, which is about three times the nickel cadmium battery, nickel metal hydride battery voltage of. Higher requirements for the power supply voltage of the electronic equipment, battery number series batteries needed can be greatly reduced. So use a combination of lithium battery is easy to get higher voltage.

(2) is higher than the energy, that is, with the weight of the lithium battery provides energy is higher than other batteries. The specific energy of lithium-ion batteries for nickel cadmium battery, nickel metal hydride batteries commonly 2 ~ 3 times. So small, lightweight portable electronic equipment.

(3) no memory effect. Nickel cadmium battery, nickel metal hydride batteries has memory effect, must be regularly discharge, or it will battery failure caused by memory effect. The lithium battery has no memory effect, don't have to ignore the amount of residual capacity, can be recharged directly. This allows the lithium battery efficiency into full play.

(4) Long service life. Lithium battery using carbon anode, carbon negative not generated in the process of charging and discharging lithium metal, in order to avoid the battery by the metal lithium inside short circuit and damage. At present, the cycle life of lithium-ion batteries can reach more than 5000 times, far higher than other kinds of cells.

(5) wide working temperature range, can generally be 30 ℃ in a Sichuan work between 0 ℃, with excellent high and low temperature discharge performance.

(6) Low self-discharge rate. Also called charge retention, self-discharge refers to how much battery automatic discharge when not in use. Lithium battery self-discharge rate was 2% ~ 5%, between 25% ~ 30% nickel cadmium battery, nickel metal hydride batteries is between 30% ~ 35%.Therefore, under the same environment lithium battery charge time longest.

(7) lithium battery does not contain any toxic elements such as mercury, cadmium, is the real green environmental protection battery.

Based on the above advantages, lithium batteries are widely used in portable electronic devices. Lithium battery, on the other hand, because of its high energy density, making it difficult to ensure the safety of the battery. Specifically, in the condition of charging, the electrolyte will be dismantled, makes the battery internal temperature and pressure rise; After discharge state, the anode in the electrolysis materials - copper melt due to internal short circuit, makes the temperature rise: in an external circuit electrical short circuit or discharge the first chapter introduction 3 through the large, due to the characteristics of high resistance, inside the battery power consumption increases, the temperature increase, may cause the oxidation and decomposition of the electrolyte, lithium battery life expectancy. In addition, if excessive discharge of the lithium battery will make the battery electrolyte in produces change, but the number of times a charging circuit can reduce because of this, thus influence the service life of lithium-ion batteries.

Due to the lithium batteries had a disadvantage of the above analysis, in the application of lithium batteries must be combined with protection circuit. The basic function of the protection circuit also want to and the above shortcomings, so we ask for lithium battery power protection chip to achieve the following basic functions: over charging protection, discharge protection, over current protection and short circuit protection. The application requirement of lithium battery by above knowable, in order to improve the service life of lithium-ion batteries and ensure the safety of the battery is used, need lithium battery protection circuit has the following features:

(1) if a battery charging voltage exceeds allowed maximum, can provide the battery discharge circuit.

(2) if the discharge voltage was below the minimum allowed battery, can provide the battery charging circuit. Is to cut off the battery and the external circuit connection, and then cut off the battery and the external circuit connection, and

(3) If the battery charge and discharge current is greater than the limit value, is to cut off the battery and the external circuit connection.

(4) When the battery back to normal, protective circuit should be able to remove the corresponding protection status, made battery can continue to work normally.

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