Lithium battery online charging and discharging -Lithium - Ion Battery Equipment

Lithium battery online charging and discharging circuit -Lithium - Ion Battery Equipment

Design of Li-ion Battery Online Charge and Discharge Management Circuit

1Characteristics of lithium-ion batteries

In recent years, the rapid development of portable electronics has led to an upgrade in battery technology. During this period, lithium-ion batteries continued to emerge and became the mainstream of the market due to their high energy density, high internal resistance, high battery voltage, high cycle times, and low self-discharge rate. According to statistics, in the field of notebook computers and mobile phones, the market share of lithium-ion batteries is 80% and 60% respectively. According to estimates by the Yano Institute of Economic Research in Japan, lithium-ion batteries are rapidly replacing traditional nickel-chromium and nickel-metal hydride batteries with an annual growth rate of 53.33%.(Lithium - Ion Battery Equipment)

Although the lithium-ion battery has the above advantages and good market prospects, it is a relatively high maintenance requirement for the circuit. In the process of application, the phenomenon of excessive charging should be strictly prevented, excessive discharge, and the discharge current should not be too large. In other words, the discharge rate should not exceed 0.2c. The charging process of a lithium-ion battery is shown in Figure 1. During the charge cycle, lithium-ion batteries test the battery's voltage and temperature before charging to determine if it can be charged. Charging is prohibited if the battery voltage or temperature exceeds the manufacturer's allowable limits. The allowable charging voltage is planned as: 2.5v~4.2v per battery; the temperature method is: 2.5℃~50℃. When the battery is in a state of deep discharge, the charger is required to be pre-charged, so that the battery can meet the conditions of fast charging; then, according to the fast charging speed recommended by the battery manufacturer, generally 1C, the charger is charged with constant current, and the battery voltage is slow rise. When the battery voltage reaches the set intermittent voltage (usually 4.1v or 4.2v), the constant current charging is interrupted, the charging current decays rapidly, and the charging enters the full charging process. In the process of full charging, the charging current gradually decays until the charging rate drops below C/10 or the charging time ends, and then goes to the top to stop charging. When charging at the top, the charger uses very little charging current to replenish the battery's energy. After charging on top for a while, turn off charging.

Generally speaking, the lower limit of the safe voltage of lithium-ion batteries is 2.4v, and the charging voltage required by the error accuracy is inaccurate, but it also needs to be matched with an appropriate over-discharge delay time, in order to coordinate the maximum power load and over-discharge maintenance requirements. When the battery is discharging, when the battery voltage is lower than the over-discharge maintenance voltage, the battery discharge should be turned off to prevent the occurrence of battery over-discharge. When the discharge current is too large, the maintenance circuit should close the battery discharge to show the over-discharge current maintenance function. The size of the maintenance current can be set according to the size of the load. It is worth noting that the maintenance circuit cannot malfunction due to the short-cycle high current of the load demand. It is necessary for the maintenance circuit to supply the maintenance delay time of different over-discharge currents to improve the stability of operation.

In addition, the maintenance function of all lithium-ion battery packs can also be performed with internal pressure maintenance through the battery's safety threshold and high temperature maintenance through the thermistor of the external circuit.

2. On-line charge and discharge processing circuit structure

Due to the relatively high requirements for the maintenance circuit of lithium-ion batteries, when planning the charging and discharging circuit, all possible situations should be fully considered and maintained to ensure the safe operation of the battery. In practical planning, lithium-ion batteries are to be used in unattended musical instruments for a long time, and the charge and discharge circuits are to actively monitor the conditions of the lithium-ion batteries, external power sources and loads, and act accordingly to ensure that the loads are very Stable operation for a long period of time and safe and efficient operation of Li-ion batteries.



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