Principle and application of lithium battery charging circuit

Lithium ion battery charging process can be divided into three stages: a trickle charge (low voltage pre-charge), constant current charging and constant voltage charging.

The lithium battery is pressure limiting constant current charging way, are all controlled by the IC chip, typical charging way is: detection for charging battery voltage, if the electricity

Down to 3 v, have to be pre charge first, 1/10 of the charging current to set current, voltage to 3 v, in the process of charging standard. Standard process for:

To set for constant current charging current and battery voltage rises to 4.20 V, the constant voltage charging, instead to keep charging voltage of 4.20 V. At this point, the charging current gradually

Fall, when the current dropped to set up 1/10 of the charging current, charging is over.

Everyone know already, the lithium ion battery anode materials for lithium cobalt oxide, the cathode is carbon.

The working principle of lithium-ion battery is refers to the principle of charging and discharging. When charging the battery, the battery has lithium ions generated in the anode, the generated lithium ions through the electrolyte to the negative movement. As a cathode carbon layer structure, it has many pores, arrived in the cathode of lithium ion is embedded into the microporous carbon layer, the embedded lithium ion, the more the higher the charge capacity.

Likewise, when to discharge the battery (i.e., we use the battery process), embedded in the cathode carbon layer of emergence, lithium ions and movement back to the anode. Back to the anode of lithium ion, the more the higher the discharge capacity. We usually mean by battery capacity is the discharge capacity.

It is not hard to see, in the process of charging and discharging lithium ion batteries, lithium ion in the motion state from the positive and negative to the anode. If we compared the image of the lithium ion battery as a rocking chair, rocking chair at both ends of the poles for the battery, and lithium ion as excellent athlete, running to and fro in the ends of the rocking chair. So, the experts gave lithium ion battery rocking-chair batteries a cute name.

The principle and application of lithium battery charging circuit

Lithium-ion batteries for its excellent properties are widely used in: mobile phones, camcorder, laptops, cordless phones, power tools, electric toys, remote control or cameras, and other portable electronic devices.

A, Lithium battery and nickel cadmium, nickel metal hydride rechargeable battery:

Lithium ion battery negative extremely graphite crystal, the anode is usually lithium oxide. Rechargeable lithium ion embedded graphite layer by the positive to the negative movement. When discharge, lithium ion from graphite crystals inside the cathode surface from moving to the anode. So, in the process of the battery charging and discharging lithium always appear in lithium ion form, rather than the form of metal lithium. So this battery is called lithium-ion batteries, lithium batteries for short.

Lithium battery has: small size, large capacity, light weight, no pollution, single section high voltage, low self-discharge rate, cell cycle times more advantages, such as, but more expensive. Nickel cadmium battery because of low capacity, self-discharge is serious, and there is pollution to the environment, are being phased out gradually. Ni-Mh batteries with higher price performance ratio, and does not pollute the environment, but only monomer voltage 1.2 V, and restrictions on the scope of use.

Second, the characteristics of lithium battery:

1, have a higher energy than energy than weight, volume;

2, high voltage, single section lithium battery voltage of 3.6 V, is equal to three nickel cadmium or nickel metal hydride rechargeable batteries in series voltage;

3, self-discharge stored for a long time, it is the battery's most prominent superiority;

4, No memory effect. Lithium battery does not exist nickel cadmium battery memory effect, so the lithium battery without before discharge,

5, Long service life. Under normal working conditions, lithium battery charge/discharge cycles is greater than 500 times;

6, can quick charge. Lithium battery can usually use 0.5 ~ 1 times the capacity of charging current, charging time to 1 ~ 2 hours;

7, can freely parallel;

8, because the battery does not contain heavy metals such as cadmium, lead, mercury, on the environment pollution-free, is contemporary the most advanced green battery;

9, high cost. Compared with other rechargeable batteries, lithium battery price is more expensive.

Three, the internal structure of lithium battery:

Lithium battery usually has two features: cylindrical and rectangular.

Inside the battery adopts spiral winding structure, with a very fine permeability and strong polyethylene film interval between positive and negative isolation material. The anode including composed of lithium cobalt oxide and lithium ion collector and current collector composed of aluminum film. Negative collected by flake carbon material of lithium ion anode and copper current collector composed of thin film. Inside the battery charger has organic electrolyte solution. Also equipped with a safety valve and PTC element, the battery in the abnormal state and the output short circuit protect cells from damage.

Single section of lithium battery voltage of 3.6 V, it is impossible to infinite capacity, therefore, will be a single section often lithium battery series, in parallel processing, in order to meet the requirements of different occasions.

Four, lithium battery charge and discharge requirements;

1, lithium battery charge: according to the structure characteristics of lithium battery, charging termination voltage should be 4.2 V, can't overcharge, otherwise it will for the anode of lithium ion to take away too much, and make a battery scrap. The charging and discharging the demand is higher, can be used for constant current, constant voltage charger to charge. Usually constant current charging 4.2 V/holiday turn to constant voltage charging, when constant voltage charging current dropped to 100 ma, should stop charging.

Charging current (mA) = 0.1 ~ 1.5 times the battery capacity (such as 1350 mAh battery, the charging current can be controlled between 135 ~ 2025 mA).Conventional charging current can choose at about 0.5 times the battery capacity, charging time is about 2 ~ 3 hours.

2, lithium-ion battery discharge:, due to the internal structure of the lithium battery is discharging lithium ion can't all to move to the positive, you must retain part of lithium ions in the cathode, in order to make sure the next rechargeable lithium ion can flow in channel. Otherwise, the battery life is reduced. In order to guarantee the graphite layer after discharge in the left part of the lithium ion, to strictly limit discharge termination of the lowest voltage, that is to say, the lithium battery can't discharge. Discharging termination voltage of 3.0 V/usually section, the lowest not less than 2.5 V/section. The time of the battery discharge and the battery capacity has the size of the discharge current. The battery discharge time (hours) = battery capacity/discharge current. Lithium battery discharge current (mA) should not be more than three times as many battery capacity.(such as a 1000 mAh battery, the discharge current should be strictly controlled within 3 a) or you will make a battery damage.

That is sold on the market at present lithium battery pack internal sealing are necessary to charge and discharge protection plate. As long as the good control outside of the charge and discharge current.

Five, the lithium battery protection circuit:

The charge and discharge protection circuit of two lithium battery is shown in figure 1.By two field-effect tube and special protection integrated block of S - 8232, charging control pipe FET2 and over discharge control FET1 are in series in the circuit, controlled by protection IC and monitor the battery voltage. When the battery voltage is up to 4.2 V, over charging protection tube FET1 cut off and stop charging. To prevent mis-operation, there generally is delay capacitance in the external circuit. When the battery is under discharge conditions, the battery voltage decreases to 2.55 V, discharge control tube FET1 cuts off and stops supplying power to the load. Overcurrent protection is that control FET1 makes its deadline and stops to load discharge when there are large current flows through the load. The purpose is to protect the battery and the field effect tube. Over-current detection is to use the field effect tube conduction resistance test for the resistance, and monitor its voltage drop. Stop discharge when the voltage drops more than set value. Generally, there will be plus time delay circuit in the circuit to distinguish between surge current and short-circuit current. The circuit has completed functions, reliable performance and strong profession. It is not easy to buy as application-specific integrated block, and is not easy to be copied by amateur.

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