Design Analysis of Battery-Based Power Management System
The battery-based power management system includes a battery and a voltage regulator circuit that supplies power to the system. The main design goals include: Battery Selection To meet the above design goals, the design of the power management system begins with the battery. The battery type has a primary battery (or non-rechargeable battery) and a rechargeable battery. Some popular rechargeable batteries include: Nickel-cadmium (NiCd) batteries have long life, high discharge rate and low cost. The advantage is a simple charging characteristic that can withstand multiple charges/discharges. Nickel-metal hydride (NiMH) battery: It has a higher energy density than NiCd battery, but its energy density is 30%~40% higher than NiCd at the expense of life. The NiMH storage effect is relatively small. When charging, NiMH uses a more complex charging algorithm and consumes some heat, so the required charging time is longer than NiCd. Lithium-ion (Li-ion) battery: high energy density and light weight. Today's lithium batteries are at the center of the cell at maximum electrochemical potential per unit weight and highest energy density. Lithium-ion batteries are safe and provide some safety measures when charging and discharging. Its energy density is twice that of a standard NiCd battery. In addition, it has a high capacity, its load characteristics are quite good, and the discharge characteristics are similar to those of NiCd. Its relatively high battery voltage (2.7~4.2V) makes many Li-ion battery packs consist of only one battery. The lifetime is 300 charge/discharge cycles and 50% capacity at 500 cycles. However, Li-ion batteries require a protection circuit that limits the peak voltage of each battery during charging and prevents the voltage drop from being too low during discharge. The protection circuit not only limits the maximum charge and discharge current, but also monitors the battery temperature. Care should be taken to short-circuit, overcharge, crush, knock, damage, penetrate, reverse polarity, expose to high temperatures or disassemble the battery when handling and testing Li-ion batteries. A battery refers to a portion of a cup, trough or other container or composite container containing an electrolyte solution and a metal electrode to generate electrical current. As technology advances, batteries are broadly referred to as small devices that generate electrical energy. Such as solar cells. The performance parameters of the battery mainly include electromotive force, capacity, specific energy and resistance. The performance parameters of the battery mainly include electromotive force, capacity, specific energy and resistance. The electromotive force is equal to the work done by the non-electrostatic force (chemical force) of the battery when the positive charge is moved from the inside of the battery to the positive electrode. The electromotive force depends on the chemistry of the electrode material and is independent of the size of the battery. The total amount of charge that the battery can output is the capacity of the battery, usually in ampere-hours. In a battery reaction, the electrical energy produced by 1 kilogram of reactive species is called the theoretical specific energy of the battery. The actual specific energy of the battery is smaller than the theoretical specific energy. Because the reactants in the battery are not completely reacted according to the battery reaction, and the internal resistance of the battery also causes the electromotive force to drop, the battery with higher energy is often referred to as a high-energy battery. The larger the area of ​​the battery, the smaller the internal resistance. The energy storage of a battery is limited. The total amount of charge that a battery can output is called its capacity. It is usually measured in ampere-hours. It is also a performance parameter of the battery. The capacity of the battery is related to the amount of electrode material, that is, to the volume of the electrode. Practical chemical batteries can be divided into two basic types: primary batteries and batteries . The current can be generated after the primary battery is made, but it is discarded when the discharge is completed. The battery is also called a secondary battery. It must be charged before use. It can be discharged after charging. It can be recharged after the discharge is completed. When the battery is charged, the electrical energy is converted into chemical energy; when discharged, the chemical energy is converted into electrical energy. Lithium polymer (Li-Pol) battery: Energy density is similar to Li-ion battery, but it is safer to use and has better packaging flexibility. Li-Pol batteries differ from Li-ion in the manufacture of ruggedness, safety and thin profile geometries. Unlike Li-ion batteries, there is no danger of flammability. Because the electrodes of Li-Pol are laminated. Some battery packs include an integrated IC protection circuit. This IC prevents large currents that can cause overheating. The battery in the lithium-ion battery pack requires separate voltage monitoring. The more batteries connected in series, the more complex the protection circuit is. Note: Do not discharge lithium-based batteries below 2.5V. Otherwise, cut off the protection circuit of the battery. All batteries will self-discharge. Self-discharge is most pronounced for nickel-based batteries. Usually, in the first 24 hours after charging, the nickel-based battery discharges 10% to 15% of its capacity, and the subsequent discharge rate is 10% to 15% per month. Li-ion self-discharge is about 5% in the first 24 hours, followed by 1% to 2%. 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Performance and charging time interval indicators, through an effective system design, to make the battery size the smallest and the lightest.
A suitable regulated output voltage is provided over a wide input voltage range, and the battery-based system operates normally as the battery voltage drops.
The power management system is required to reduce the printed circuit board size.
The minimum heat consumption of the power management system should eliminate complex thermal management, which increases weight and cost.
Optimized circuit wiring for power management systems should avoid electromagnetic interference.
Highly reliable power management system.
Use only Li-ion batteries with protective circuits.