Lithium-ion battery charging method for energy storage

　　Author ：Iflowpower – Portable Power Station Supplier

Compared with the old technologies such as nickel-cadmium, lithium-ion battery chemistry technology greatly improves the power density of portable equipment, and follows the normal operation time of these systems when single charging is. The self-discharge ratio of the lithium-ion battery is half of nickel-cadmium and nickel metal hydrides, which also helps the shelf life, allows the equipment to charge, so that customers do not have to buy before use. The disadvantage of lithium ions is more complex than old technology than early chemistry.

However, cautious management can be used to maximize the power delivery of lithium ions, not only supply a better experience, but also allows you to narrow your design to use smaller batteries. Since the battery accounts for a significant ratio in the size and weight of the wearable device, it is remarkable by replacing a charging circuit to another charging circuit. The key problem of lithium-ion batteries is because they are very sensitive to excessive charging, because too high voltage can cause material stress, thus shortening battery life.

If the charge exceeds the voltage of 4.2V per battery, they will also bring security risks. Low-cost charging circuits can be overcharged, because the battery does not reach the actual limit.

They use so-called charging and running strategies, this strategy has the advantage that it looks quickly. This strategy uses the characteristics of the lithium ion charging curve, which can be divided into four key stages. The first phase uses a constant current to supply the battery.

With the battery, its voltage is more or less linear. The voltage is flattened in the vicinity of the peak, at which time the charger can stop. However, only about 85% charge at this time, resulting in the use time to be low in theory.

In addition, due to safety reasons, the cutoff voltage is typically set below the maximum voltage, further reduces the maximum charge applied to the battery. The cutoff voltage is 3.8V rather than the typical maximum of 4.

2V, so 60% of the battery capacity is available. The rest of the charging is performed during saturation or constant voltage phase. Although the fast charger can reduce the time required to reach the saturation phase by adding charging current, this has the effect of extending the saturation phase, and carefully and accurately manages the saturation stage to guard against stress.

Figure 1: Charging stage of lithium ion batteries, including thermal adjustment stages under high temperature conditions. It is difficult to test the battery full of overflow, so time or current level is used as a proxy to indicate that the battery has been close to complete charging. Usually, the saturation charging is about two hours, thereby supplying reasonable set of time.

During saturation charging, current index declines. When the current reaches about 3% of the level used in the first phase, the battery is generally considered to be fully charged and the process can stop. The voltage used during saturated charging is adjusted to one percent or better.

Circuits performing a saturated charge can use current testing and press to manage processes to ensure that the power will be cut after a period of time, and the metal lithium accumulate, resulting in a fire. Temperature is also useful in control charging. In the first stage, the internal resistance is relatively low, the battery will not be tapered.

Once entering a saturation phase, the battery will become warmer. Therefore, the temperature sensor is related to ensuring that the battery will not overheat and have a safe risk is very important. Battery manufacturers will provide a safe temperature limit for their products, and typically supply thermistors that can be used with ADCs or comparator circuits in the charger circuit in the battery pack.

The charging process is to be charged before the depth depletion. This uses trickle charging to resume the chargeable battery - tested their voltage will be lower than 3V. Once the trickle process is supplied with sufficient charge, the voltage will rise to 3V or more and the normal first stage charging process can be taken over.

Linglurt's LTC4065 charger IC uses a small size DFN package that supplies how to organize feedback loops to support the various charging modes required for lithium ion batteries. The device supports constant current and constant voltage charging methods, as well as a constant temperature to allow effective charging proximity to the battery. In order to support high temperature charging, the LTC4065 has a heat limit circuit.

This can set the charging current in accordance with a typical ambient temperature (rather than the worst case), and ensure that the charger is automatically reduced in the worst case. In LTC4065, three amplifiers feedback loops control constant current, constant voltage, and constant temperature mode. The fourth amplifier feedback loop is used to add the output impedance of the current source pair to ensure that one drain current is just a thousand times of the second drain current.

A separate feedback loop for constant current and constant voltage operations forces the charger based on any model that attempts to minimize the charging current. Another amplifier output is saturated, which effectively eliminates its loop from the system. When in constant current mode, it is accurately driven to a 1v.

Prog pin to program the current by using a percent tolerance resistor (rPROG). When the constant voltage mode is loved, the constant voltage loop drives its inverted input to the internal reference voltage. The internal resistor divider ensures that the battery voltage remains at 4.

2V.Prog pin voltage can also indicate the charging current in constant voltage mode. In a typical work, the charging period begins with constant-current mode - the current delivered to the battery is equal to 1000V / rProg.

If the power consumption of the LTC4065 is close to 115°C, the limit temperature amplifier will begin to lower the charging current, limit the temperature of the chip in about 115°C. Once the temperature restriction mode is exited, the LTC 4065 will return constant current mode or enter the constant voltage mode from the constant temperature mode. Whether it is mode, the voltage of the PROG pin is proportional to the current delivered to the battery.

Internal press-of-time circuitry and trickle charging management have improved the functions required for effective lithium-ion battery management. The device supplies 0.6% floating voltage accuracy, only two external components.

When the input power is removed, the LTC4065 automatically enters a low current state and the battery leakage is lowered to 1.μA below. After the power is applied, the LTC4065 can enter the shutdown mode and drop the power supply to 20.

μA below. Figure 2: Charging status flow chart LTC4065 decision similar to this. Similar to LTC4065, MaximIntegrated MAX1551 also has thermal limiting functions, optimal charging, without being thermally restricted by the worst case battery and input voltage.

When the heat limit is reached, the MAX 15551 and the MAX 1555 will not completely stop charging, but gradually reduce the charging current, which helps maintain function when cooling in the system. The SOT23 package is used, similar to the MAX1551 and MAX 1555, the MCP73811 developed by Microchiptechnology is supplied with constant pressure and constant current charging, the latter only programmed by external resistance, and is equipped with a built-in heat sensor control temperature limit charging. The BQ2409X series of Texas Instruments (TI) is a highly integrated linear charger device, facing space-oriented portable use.

These ICs are designed for USB port power or may not be adjusted AC adapters with high input voltage range and input overvoltage protection. BQ2904X performs adjustment, constant current and constant voltage charging. In all charging stages, internal control loop monitors IC junction temperature and lower charging current when exceeding internal temperature thresholds.

Although the combination of lithium-ion batteries to charge techniques allows building portable and wearable systems to make the build portable and wearable systems make longer, the longest function is supplied, and the battery size can be reduced. The best trade-off between small to weight and life. .