A "natural" magazine sub s "science reporting" (Sci.Report) published a heavy research Fudan University, Professor Wu Yuping Task Force. The latest research on an aqueous solution of lithium battery systems, lithium battery performance by 80%. Electric car charging only need 10 seconds to travel 400 kilometers, this battery cost, security is not easy explosion.
Wu Yuping research group showed reporters on the 13th of this lithium battery system. A thin layer of metallic lithium, a special composite membrane tightly wrapped, to be placed in the pH value was in the neutral aqueous solution, an average, can be made with the traditional cathode materials in lithium ion battery spinel manganate lithium assembly charging voltage of 4.2V, the discharge voltage of 4.0V new water lithium battery, this result greatly exceeded the aqueous solution of the theoretical decomposition voltage 1.23V.
According to reports, the commonly used organic electrolyte lithium-ion battery. The large energy storage system, the traditional high cost of lithium batteries, the high requirements on the production conditions, and because the physical and chemical properties of the organic electrolyte, there is greater safety hazards. This is the new energy products such power car is not the main obstacle to large-scale promotion.
Wu Yuping Task Force of the achievements on the development of a new low-cost, easy to mass production, possible safety environmental protection battery system. Allegedly, the novel water lithium using the aqueous solution as electrolyte, a flame retardant enhanced, so that the battery during use less hot fever, high safety performance; composite film made of a polymer material and an inorganic material, capable of the energy loss of the battery below 5%.
It is estimated that if this battery for mobile phones, the battery supplier of the same size at least be able to extend the phone talk time doubled, the cost is less than half of the original; same used in automotive pollution on the environment than existing lithium The battery is much smaller.
Wu Yuping said U.S. Energy Research Institute "aiming" in the study, and his hope to reach a cooperation intention. He also hoped that a forward-looking enterprise cooperation with the country. He said, "novel aqueous lithium in life can be specifically applied to on all sides, I hope the water lithium breakthrough to end, the consumers of safe, accepted on costs, the solution to the current global faltering electric car industry .
2013年3月20日星期三
Competition in Car Lithium Battery Development
Rechargeable battery is largely about the environmental performance of electric vehicles and vehicle costs. Car rechargeable batteries not only need to meet the energy capacity of the vehicle farther from the decision, the instantaneous current input and output, as well as to prevent abnormal heat and fire safety requirements, and also need to meet in order to make electric cars that can be accepted by ordinary consumers, cost requirements, being the fierce competition in the development for enterprises. The development of the lithium-ion rechargeable batteries in the future will focus on the following three elements: (1) reduce the cost of energy per unit of capacity; (2) to ensure security; (3) inhibition of charging and discharging a result of deterioration. Especially inhibiting the deterioration of charge and discharge causes, relationship to the user the feeling of use of electric vehicles, and contains the total cost of the maintenance costs, including, therefore important factor can not be ignored.
The Cathode Material choices vary
The performance and cost of the battery depends on the material, structure, and control, of which the most important is the choice of materials. Battery manufacturers must make the optimal choice from a variety of candidate materials. Are already in production or plan the next 1 to 2 years of mass production of lithium-ion rechargeable battery cathode material, in accordance with the different material combinations with lithium, divided into four kinds the ternary manganese, NCA and iron phosphate class (Figure 1). Cathode materials are generally of the conventional lithium battery using lithium cobalt oxide (LiCoO2). But the use of a positive electrode of lithium cobaltate when charging the crystal structure is not stable enough to use in the vehicle-mounted battery, the existence of the security issue. Develop in-vehicle lithium battery technology to try and develop a new material instead of lithium cobalt oxide.
Be referred to as a ternary material of lithium cobalt oxide part of the cobalt, nickel and manganese is substituted by cobalt, nickel, manganese, three components, to improve the stability of the material. Ternary [Li (Ni-Mn-Co) O2] battery materials manufacturers including the announcement of the shallow the Suzuki extended-range electric vehicle supply lithium batteries, Sanyo Electric, and developed for Honda PHEV supply battery GS soup with Honda joint venture company Blue Energy Japan.
The NCA based material NCA is nickel, cobalt, aluminum, three word prefix abbreviation. NCA class of materials made of aluminum instead of manganese ternary material. NCA class material [Li (Ni-Co-Al) O2] is the joint venture of Toyota and Panasonic Primearth EV Energy with its production of lithium battery is equipped in the Prius plug-in hybrid. NCA class lithium generally has excellent energy density, but there are still to be solved in terms of safety. Primearth EV Energy Company in order to improve the lithium-ion rechargeable battery security, improve the heat resistance of coated ceramic layer on the negative measures, so as to strengthen the safety performance.
The manganese-based material using lithium manganese oxide (LiMn2O4). Such materials have been widely adopted by the battery manufacturers in Japan, South Korea and the United States is now the mainstream car battery. Major manufacturers including Automotive Energy Supply to supply batteries Nissan LEAF (Chinese name: hear the wind) for the the Mitsubishi iMiEV supply battery Lithium Energy Japan, LG Chem to supply batteries for GM's Volt, as well as Daimler, BMW and Beijing Automotive supply batteries, Johnson Controls-Saft (Johnson Controls-Saft), etc.. The manganese-based material compared with the ternary and NCA based material, in theory, the energy capacity density is lower, but the lithium atoms, manganese atoms, and an oxygen atom capable of forming a solid crystal structure, and therefore thermal stability is excellent, safe. In addition, manganese, cobalt and nickel, compared the prices of raw materials cheaper cost advantage. The prices of raw materials in descending order of the cobalt, nickel, manganese, if the price of cobalt is seen as 10 words, then nickel is 5, and manganese is less than 1.
The material of ferrous phosphate (LiFePO4) cathode materials for Chinese manufacturers to use more. Such material tightly due to phosphorus (P) and oxygen (O), even when the battery internal heat, the crystal structure also difficult destruction is therefore highly safe. Ago due to low electrical conductivity of the iron phosphate-based material, there is a problem, but difficult to improve the output power supply in the cathode material coated fine CFC improved characteristics, greatly promote the process of practical. The advantage of such materials in addition to the safety, another advantage in that the cost of materials. Raw material prices of iron manganese also cheap, estimated about only manganese fraction of. But there are also technical personnel noted that the process for manufacturing of such material are high cost, so it is difficult to play out the cost advantages of the material itself. Due to the need to create prevent iron oxidation manufacturing environment, but also for the cathode material coated with carbon quality management process also takes manpower and resources, and therefore contain manufacturing costs, including the total cost is not necessarily cheaper.
Cost target is 20,000 yen / kWh reduced consumer products with lithium batteries quite
Currently, the Japanese manufacturer of car lithium battery costs about 10 to 12 million yen / kWh, Chinese manufacturers for its half. GM's Volt battery costs 100,000 yen / kWh to calculate the cost of electric car battery with 16kwh battery for 1.6 million yen, The Nissan LEAF with 24kwh battery for 2.4 million yen (Figure 2). Only the cost of the battery is equivalent to the price of a car. In other words, EV and REV (modified EV) compared with the same level of gasoline cars, the cost will be twice as high. To promote the popularization of electric vehicles, battery costs must be reduced.
Car lithium battery cost targets consumer products is reduced to the level of lithium batteries. Consumer products with lithium batteries cost about 20,000 yen / kWh. 20,000 yen / kWh, the Volt's battery costs 320,000 yen, LEAF 480,000 yen. Battery costs can be reduced by 1.28 million yen and 1.92 million yen. The cost of the battery will decrease reflected in vehicle prices, then, to the Volt price can be reduced to 2 million yen, LEAF can be reduced to 1.85 million yen. If the cost can be reduced to this level, the electric car will be able to achieve the average consumer can afford the price.
20,000 yen / kWh cost is also consistent with the target value of the Japanese and Chinese car lithium battery development blueprint. Preparation of the car in Japan's New Energy and Industrial Technology Development Organization (NEDO) rechargeable battery development blueprint, the cost target for 2015 dropped to 30,000 yen / kWh 20,000 yen / kWh in 2020 for year three. In electric vehicle technology blueprint released by the Chinese government in 2015, China's battery cost target value of $ 1,500 / kWh (about 18,000 yen) (Figure 3).
The attitude of the battery suppliers for car battery cost 20,000 yen / kWh support the possibility of this goal. Nissan joint venture between NEC executives in an interview with Reuters in September 2010, said the company is promoting the development of lithium-ion rechargeable battery, the goal is to have 2017, its price compared with the products now halved performance doubled. Half the price doubled the performance dropped to a quarter of the current means the price per kWh. Assuming the current cost of the battery for 100,000 yen / kWh, the 2017 cost is 25,000 yen / kWh. In addition, LG Chemical Company executives said in February 2011 at the International Conference on the price of the company that will be mass produced lithium-ion rechargeable battery 350 to $ 400 / kWh (about 28,000 to 32,000 yen). LG Chem said 350 to 400 U.S. dollars / kWh prices considering the cost of the company will be reduced.
A driving force to reduce the prices of the battery unit capacity is a high capacity, and improve production efficiency. High capacity, consumer products, energy density lithium nearing 250Wh/kg, the and car lithium battery is only about 100Wh/kg. Car lithium battery, there is scope to improve the energy density. Battery Unit another driving force is reduced to improve production efficiency, it may be mainly adopted to expand the scale to obtain the mass-production effect, to improve the process and reduce the cost of production equipment and other measures to achieve. Automotive Energy Supply Company regarding its future car rechargeable battery production plans, 50,000 EV battery unit available for mass production from 2011, the increase in production by 2013 will amount to 500,000 EV
The deterioration of the battery performance problems can not be ignored
Car lithium battery elements can not be ignored is the deterioration of the battery problem. Buy a new car to the scrap car to use a minimum of 10 years. If the battery obvious deterioration during this period, the user is forced to replace the batteries of electric vehicles, it will damage the user experience, the user will increase the economic burden.
The rechargeable battery using the electrochemical reaction of charge and discharge, and therefore it is inevitable to cause deterioration due to repeated use. EV users must be aware of in advance of the: EV 5 years after the deterioration of the battery may cause the battery capacity is reduced by 20 to 30%. With a capacity of 25kWh battery, can travel 150km of EV example, the battery capacity decline may lead to shorten the travel distance of 30 ~~ 50km. Perhaps the user wants the performance deterioration of the battery replaced, in this case, even if the battery is priced at 20,000 yen / kWh battery replacement costs 500,000 yen. Assume that every 5 years would cost 500,000 yen replace the battery, then the annual cost burden is 100,000 yen, the user needs to be considered in advance EV maintenance fees.
As mentioned above, the battery life is directly related to the user's EV cost of ownership, so it will become a key element in the car charging battery development. Future, widespread popularity EV and PEHV standing with costs, but also reduce the user's vehicle to the point of view of the cost of ownership and cost assessment, on-board lithium battery. Concern as a strong anti-deterioration performance car lithium battery is a the negative lithium titanate battery. The negative electrode of lithium batteries generally use graphite, but the durability can be improved using the lithium titanate. Toshiba experimental results show that the lithium titanate negative electrode of the lithium battery life when compared with the use of graphite in the traditional lithium may be extended to 6 times. In this case, you do not need during the life of the vehicle due to the deterioration of the battery and replace the battery, it will not cause the user's vehicle with rising costs. Toshiba is currently in mass production car lithium battery using lithium titanate addition to Mitsubishi Motors of this battery will be on the company's EV, Honda is also considering for the company developed the Fit EV.
The lithium-ion rechargeable battery technology is still in its development stage enterprises in order to further technological progress in the fierce competition. In the future, companies develop in-vehicle lithium battery, not only in energy capacity, cost, and security there is often a shift in the relationship between the elements of the (Trade-off) aspects to achieve optimization, but also stand the impact of performance degradation, and contains maintenance fees, including the cost of ownership perspective, comprehensive performance evaluation of the battery.
The Cathode Material choices vary
The performance and cost of the battery depends on the material, structure, and control, of which the most important is the choice of materials. Battery manufacturers must make the optimal choice from a variety of candidate materials. Are already in production or plan the next 1 to 2 years of mass production of lithium-ion rechargeable battery cathode material, in accordance with the different material combinations with lithium, divided into four kinds the ternary manganese, NCA and iron phosphate class (Figure 1). Cathode materials are generally of the conventional lithium battery using lithium cobalt oxide (LiCoO2). But the use of a positive electrode of lithium cobaltate when charging the crystal structure is not stable enough to use in the vehicle-mounted battery, the existence of the security issue. Develop in-vehicle lithium battery technology to try and develop a new material instead of lithium cobalt oxide.
Be referred to as a ternary material of lithium cobalt oxide part of the cobalt, nickel and manganese is substituted by cobalt, nickel, manganese, three components, to improve the stability of the material. Ternary [Li (Ni-Mn-Co) O2] battery materials manufacturers including the announcement of the shallow the Suzuki extended-range electric vehicle supply lithium batteries, Sanyo Electric, and developed for Honda PHEV supply battery GS soup with Honda joint venture company Blue Energy Japan.
The NCA based material NCA is nickel, cobalt, aluminum, three word prefix abbreviation. NCA class of materials made of aluminum instead of manganese ternary material. NCA class material [Li (Ni-Co-Al) O2] is the joint venture of Toyota and Panasonic Primearth EV Energy with its production of lithium battery is equipped in the Prius plug-in hybrid. NCA class lithium generally has excellent energy density, but there are still to be solved in terms of safety. Primearth EV Energy Company in order to improve the lithium-ion rechargeable battery security, improve the heat resistance of coated ceramic layer on the negative measures, so as to strengthen the safety performance.
The manganese-based material using lithium manganese oxide (LiMn2O4). Such materials have been widely adopted by the battery manufacturers in Japan, South Korea and the United States is now the mainstream car battery. Major manufacturers including Automotive Energy Supply to supply batteries Nissan LEAF (Chinese name: hear the wind) for the the Mitsubishi iMiEV supply battery Lithium Energy Japan, LG Chem to supply batteries for GM's Volt, as well as Daimler, BMW and Beijing Automotive supply batteries, Johnson Controls-Saft (Johnson Controls-Saft), etc.. The manganese-based material compared with the ternary and NCA based material, in theory, the energy capacity density is lower, but the lithium atoms, manganese atoms, and an oxygen atom capable of forming a solid crystal structure, and therefore thermal stability is excellent, safe. In addition, manganese, cobalt and nickel, compared the prices of raw materials cheaper cost advantage. The prices of raw materials in descending order of the cobalt, nickel, manganese, if the price of cobalt is seen as 10 words, then nickel is 5, and manganese is less than 1.
The material of ferrous phosphate (LiFePO4) cathode materials for Chinese manufacturers to use more. Such material tightly due to phosphorus (P) and oxygen (O), even when the battery internal heat, the crystal structure also difficult destruction is therefore highly safe. Ago due to low electrical conductivity of the iron phosphate-based material, there is a problem, but difficult to improve the output power supply in the cathode material coated fine CFC improved characteristics, greatly promote the process of practical. The advantage of such materials in addition to the safety, another advantage in that the cost of materials. Raw material prices of iron manganese also cheap, estimated about only manganese fraction of. But there are also technical personnel noted that the process for manufacturing of such material are high cost, so it is difficult to play out the cost advantages of the material itself. Due to the need to create prevent iron oxidation manufacturing environment, but also for the cathode material coated with carbon quality management process also takes manpower and resources, and therefore contain manufacturing costs, including the total cost is not necessarily cheaper.
Cost target is 20,000 yen / kWh reduced consumer products with lithium batteries quite
Currently, the Japanese manufacturer of car lithium battery costs about 10 to 12 million yen / kWh, Chinese manufacturers for its half. GM's Volt battery costs 100,000 yen / kWh to calculate the cost of electric car battery with 16kwh battery for 1.6 million yen, The Nissan LEAF with 24kwh battery for 2.4 million yen (Figure 2). Only the cost of the battery is equivalent to the price of a car. In other words, EV and REV (modified EV) compared with the same level of gasoline cars, the cost will be twice as high. To promote the popularization of electric vehicles, battery costs must be reduced.
Car lithium battery cost targets consumer products is reduced to the level of lithium batteries. Consumer products with lithium batteries cost about 20,000 yen / kWh. 20,000 yen / kWh, the Volt's battery costs 320,000 yen, LEAF 480,000 yen. Battery costs can be reduced by 1.28 million yen and 1.92 million yen. The cost of the battery will decrease reflected in vehicle prices, then, to the Volt price can be reduced to 2 million yen, LEAF can be reduced to 1.85 million yen. If the cost can be reduced to this level, the electric car will be able to achieve the average consumer can afford the price.
20,000 yen / kWh cost is also consistent with the target value of the Japanese and Chinese car lithium battery development blueprint. Preparation of the car in Japan's New Energy and Industrial Technology Development Organization (NEDO) rechargeable battery development blueprint, the cost target for 2015 dropped to 30,000 yen / kWh 20,000 yen / kWh in 2020 for year three. In electric vehicle technology blueprint released by the Chinese government in 2015, China's battery cost target value of $ 1,500 / kWh (about 18,000 yen) (Figure 3).
The attitude of the battery suppliers for car battery cost 20,000 yen / kWh support the possibility of this goal. Nissan joint venture between NEC executives in an interview with Reuters in September 2010, said the company is promoting the development of lithium-ion rechargeable battery, the goal is to have 2017, its price compared with the products now halved performance doubled. Half the price doubled the performance dropped to a quarter of the current means the price per kWh. Assuming the current cost of the battery for 100,000 yen / kWh, the 2017 cost is 25,000 yen / kWh. In addition, LG Chemical Company executives said in February 2011 at the International Conference on the price of the company that will be mass produced lithium-ion rechargeable battery 350 to $ 400 / kWh (about 28,000 to 32,000 yen). LG Chem said 350 to 400 U.S. dollars / kWh prices considering the cost of the company will be reduced.
A driving force to reduce the prices of the battery unit capacity is a high capacity, and improve production efficiency. High capacity, consumer products, energy density lithium nearing 250Wh/kg, the and car lithium battery is only about 100Wh/kg. Car lithium battery, there is scope to improve the energy density. Battery Unit another driving force is reduced to improve production efficiency, it may be mainly adopted to expand the scale to obtain the mass-production effect, to improve the process and reduce the cost of production equipment and other measures to achieve. Automotive Energy Supply Company regarding its future car rechargeable battery production plans, 50,000 EV battery unit available for mass production from 2011, the increase in production by 2013 will amount to 500,000 EV
The deterioration of the battery performance problems can not be ignored
Car lithium battery elements can not be ignored is the deterioration of the battery problem. Buy a new car to the scrap car to use a minimum of 10 years. If the battery obvious deterioration during this period, the user is forced to replace the batteries of electric vehicles, it will damage the user experience, the user will increase the economic burden.
The rechargeable battery using the electrochemical reaction of charge and discharge, and therefore it is inevitable to cause deterioration due to repeated use. EV users must be aware of in advance of the: EV 5 years after the deterioration of the battery may cause the battery capacity is reduced by 20 to 30%. With a capacity of 25kWh battery, can travel 150km of EV example, the battery capacity decline may lead to shorten the travel distance of 30 ~~ 50km. Perhaps the user wants the performance deterioration of the battery replaced, in this case, even if the battery is priced at 20,000 yen / kWh battery replacement costs 500,000 yen. Assume that every 5 years would cost 500,000 yen replace the battery, then the annual cost burden is 100,000 yen, the user needs to be considered in advance EV maintenance fees.
As mentioned above, the battery life is directly related to the user's EV cost of ownership, so it will become a key element in the car charging battery development. Future, widespread popularity EV and PEHV standing with costs, but also reduce the user's vehicle to the point of view of the cost of ownership and cost assessment, on-board lithium battery. Concern as a strong anti-deterioration performance car lithium battery is a the negative lithium titanate battery. The negative electrode of lithium batteries generally use graphite, but the durability can be improved using the lithium titanate. Toshiba experimental results show that the lithium titanate negative electrode of the lithium battery life when compared with the use of graphite in the traditional lithium may be extended to 6 times. In this case, you do not need during the life of the vehicle due to the deterioration of the battery and replace the battery, it will not cause the user's vehicle with rising costs. Toshiba is currently in mass production car lithium battery using lithium titanate addition to Mitsubishi Motors of this battery will be on the company's EV, Honda is also considering for the company developed the Fit EV.
The lithium-ion rechargeable battery technology is still in its development stage enterprises in order to further technological progress in the fierce competition. In the future, companies develop in-vehicle lithium battery, not only in energy capacity, cost, and security there is often a shift in the relationship between the elements of the (Trade-off) aspects to achieve optimization, but also stand the impact of performance degradation, and contains maintenance fees, including the cost of ownership perspective, comprehensive performance evaluation of the battery.
2013年3月14日星期四
The Role of Capacitor in the Circuit
In the DC circuit, the capacitor is equivalent to the disconnection. The capacitor is a storage charge element, is the most commonly used one of the electronic components.
This was from the capacitor structure on the start. Most simple capacitor is made on the both ends of the plate and the intermediate insulating dielectric (including air) [1] constitute. Energized, the plate charged, forming a voltage (potential difference), but due to the insulating material of the middle, so the entire capacitor is not electrically conductive. However, such a situation is a prerequisite of the not exceed the threshold voltage (breakdown voltage) of the capacitor under. We know, no substances are relatively insulated, when the material both ends of the voltage is increased to a certain extent, the material can be electrically conductive, we call this voltage is called the breakdown voltage. The capacitor is no exception, after the capacitor is the breakdown is not an insulator. However, at the secondary level, this voltage in the circuit is not done so in the breakdown voltage can be used as an insulator see.
However, in an AC circuit, because the direction of the current time as a function of changes. The capacitor charge-discharge process of the time, this time, a changing electric field is formed between the plates, while the electric field is also a function of change over time. In fact, the current through the field in the form adopted in between the capacitors.
In secondary schools, there is a saying called pass AC resistive DC is the capacitance of this nature.
The role of capacitance:
1) bypass
Bypass capacitor is an energy storage device to provide energy for local devices, which enables the output of the regulator homogenization, reducing the load demand. Like small rechargeable battery, bypass capacitor can be charged to the device to discharge. To minimize impedance bypass capacitor as close as possible to the load device powered power supply pin and ground pins. This can be well prevented the elevation of the ground potential caused by the input value is too large, and noise. The ground potential is connected in a voltage drop when a large current glitches.
2) decoupling
Decoupling, also known as decoupling. From the circuit can always be zone is divided into the drive source and the driven load. If the load capacitance is relatively large, the drive circuit capacitor charging should be discharge, to complete the transition of the signal at the rising edge of the steep, relatively large current, current to drive so it will absorb a lot of supply current, the circuit the inductance and resistance (especially on the chip pin inductance, will produce rebound), such a current phase for the normal situation is actually a kind of noise, will affect the normal working of the previous stage, which is called the "coupled" .
Decoupling capacitor is to play the role of a "battery", to meet a change in drive circuit current, to avoid mutual coupling between the interference.
Bypass capacitor and decoupling capacitor combination will be easier to understand. Actual bypass capacitor is decoupled, just bypass capacitor generally refers to the high-frequency bypass to improve high-frequency switching noise is a low impedance to vent anti pathway. Frequency bypass capacitor are generally relatively small, and generally according to the resonant frequency such as 0.1μF, 0.01μF; away coupling capacitor is generally large, it may be 10μF or greater, according distributed parameter circuit, and change the size of the drive current to determine. The bypass is the interference in the input signal as filtered object Decoupling of the output signal of the interference as filtered object, and to prevent return the power of an interference signal. This should be their essential difference.
3) filtering
(Assuming said capacitor is pure capacitance), the greater the capacitance, the smaller the impedance, the higher frequency by theory. But in fact most of the more than 1μF capacitance electrolytic capacitors, the inductance component, high frequency instead impedance increases. Sometimes see a larger electrolytic capacitor manufacturer in parallel with a capacitance of a small capacitor, this time a large capacitor through the low-frequency, small capacitor through high frequency. The capacitance of the role is to pass a high impedance low-pass high-frequency resistance low frequency. Higher capacitance increases the low frequency, the easier to pass. Specific filtering, large capacitors (1000μF) low-frequency filter, small capacitance (20pF) high-frequency filter. Had friends vividly than the filter capacitor as "reservoirs". Since both ends of the capacitor voltage is not mutation Therefore, the higher the frequency the greater the attenuation can be very image of the said capacitor like a pond, not caused by changes in the water due to the addition of a few drops of water or evaporation. It converted to voltage changes in the current changes, the higher the frequency, the greater the peak current, so that the buffer voltage. Filtering is charging, the discharge process.
4) Energy Storage
The energy storage capacitor charge is collected through the rectifier , and the stored energy is transmitted via the inverter leads to the power supply output terminal. The voltage rating of 40 ~ 450VDC, capacitance values between 220 ~ 150 000μF aluminum electrolytic capacitors (such as EPCOS B43504 or B43505) is more commonly used. According to the different power requirements, the device is sometimes used in the form of series, parallel, or combinations thereof, and the power level exceeds the power of 10KW, usually larger tank shaped spiral terminal capacitor.
This was from the capacitor structure on the start. Most simple capacitor is made on the both ends of the plate and the intermediate insulating dielectric (including air) [1] constitute. Energized, the plate charged, forming a voltage (potential difference), but due to the insulating material of the middle, so the entire capacitor is not electrically conductive. However, such a situation is a prerequisite of the not exceed the threshold voltage (breakdown voltage) of the capacitor under. We know, no substances are relatively insulated, when the material both ends of the voltage is increased to a certain extent, the material can be electrically conductive, we call this voltage is called the breakdown voltage. The capacitor is no exception, after the capacitor is the breakdown is not an insulator. However, at the secondary level, this voltage in the circuit is not done so in the breakdown voltage can be used as an insulator see.
However, in an AC circuit, because the direction of the current time as a function of changes. The capacitor charge-discharge process of the time, this time, a changing electric field is formed between the plates, while the electric field is also a function of change over time. In fact, the current through the field in the form adopted in between the capacitors.
In secondary schools, there is a saying called pass AC resistive DC is the capacitance of this nature.
The role of capacitance:
1) bypass
Bypass capacitor is an energy storage device to provide energy for local devices, which enables the output of the regulator homogenization, reducing the load demand. Like small rechargeable battery, bypass capacitor can be charged to the device to discharge. To minimize impedance bypass capacitor as close as possible to the load device powered power supply pin and ground pins. This can be well prevented the elevation of the ground potential caused by the input value is too large, and noise. The ground potential is connected in a voltage drop when a large current glitches.
2) decoupling
Decoupling, also known as decoupling. From the circuit can always be zone is divided into the drive source and the driven load. If the load capacitance is relatively large, the drive circuit capacitor charging should be discharge, to complete the transition of the signal at the rising edge of the steep, relatively large current, current to drive so it will absorb a lot of supply current, the circuit the inductance and resistance (especially on the chip pin inductance, will produce rebound), such a current phase for the normal situation is actually a kind of noise, will affect the normal working of the previous stage, which is called the "coupled" .
Decoupling capacitor is to play the role of a "battery", to meet a change in drive circuit current, to avoid mutual coupling between the interference.
Bypass capacitor and decoupling capacitor combination will be easier to understand. Actual bypass capacitor is decoupled, just bypass capacitor generally refers to the high-frequency bypass to improve high-frequency switching noise is a low impedance to vent anti pathway. Frequency bypass capacitor are generally relatively small, and generally according to the resonant frequency such as 0.1μF, 0.01μF; away coupling capacitor is generally large, it may be 10μF or greater, according distributed parameter circuit, and change the size of the drive current to determine. The bypass is the interference in the input signal as filtered object Decoupling of the output signal of the interference as filtered object, and to prevent return the power of an interference signal. This should be their essential difference.
3) filtering
(Assuming said capacitor is pure capacitance), the greater the capacitance, the smaller the impedance, the higher frequency by theory. But in fact most of the more than 1μF capacitance electrolytic capacitors, the inductance component, high frequency instead impedance increases. Sometimes see a larger electrolytic capacitor manufacturer in parallel with a capacitance of a small capacitor, this time a large capacitor through the low-frequency, small capacitor through high frequency. The capacitance of the role is to pass a high impedance low-pass high-frequency resistance low frequency. Higher capacitance increases the low frequency, the easier to pass. Specific filtering, large capacitors (1000μF) low-frequency filter, small capacitance (20pF) high-frequency filter. Had friends vividly than the filter capacitor as "reservoirs". Since both ends of the capacitor voltage is not mutation Therefore, the higher the frequency the greater the attenuation can be very image of the said capacitor like a pond, not caused by changes in the water due to the addition of a few drops of water or evaporation. It converted to voltage changes in the current changes, the higher the frequency, the greater the peak current, so that the buffer voltage. Filtering is charging, the discharge process.
4) Energy Storage
The energy storage capacitor charge is collected through the rectifier , and the stored energy is transmitted via the inverter leads to the power supply output terminal. The voltage rating of 40 ~ 450VDC, capacitance values between 220 ~ 150 000μF aluminum electrolytic capacitors (such as EPCOS B43504 or B43505) is more commonly used. According to the different power requirements, the device is sometimes used in the form of series, parallel, or combinations thereof, and the power level exceeds the power of 10KW, usually larger tank shaped spiral terminal capacitor.
2013年3月5日星期二
White LED Driver Must have Conditions
In recent years portable electronic equipment mostly switched to the forward voltage is 6V (20mA), the white LED as a backlight of the LCD, such as a mobile phone takes about 3 ~ 4 white LEDs general lithium ion battery, however, the discharge voltage is often less than 3. 6V, therefore must use in order to comply with the white LED forward voltage 3 6V demand, boost circuit in order to obtain the desired effect, means that the white LED driver must have to meet: even if the battery output voltage required for normal forward voltage UF-down, the drive can also be provided for the white LED.
Poor white LED's forward voltage drop match early white LED driver should match the current limiting resistor, to compensate for the forward voltage differences, in order to ensure white LED brightness consistency. However, the newly developed white LED driver IC supply voltage can not maintain a constant brightness. Upgrade and adjust the battery voltage driver IC can be open or closed loop controller, charge pump or inductive converter with voltage or current output.
In most applications, the white LED is in parallel or in series together. However, in individual cases, it also can be mixed in series and parallel configurations. LED connection in series or in parallel or hybrid depending on the needs of the application, each configuration has its own advantages and shortcomings.
1. The series. The white LED has a the similar diode forward voltage and current characteristics. Since the white LED brightness almost entirely by the current control, therefore, just use the same or match the current, two white LED light can be obtained the same brightness, without having to consider the difference of the forward voltage. White LED connected in series to ensure that its current is the same, therefore all white LED brightness is consistent.
2. The parallel. Most parallel white LED configurations use a constant voltage or constant current drive, and the drive is used depends on the specific application requirements. Parallel white LED driver in a constant voltage topology is very simple, the drive can be open-loop voltage output switching DC / DC regulator converter. Each white LED series with a current limiting resistor to set the current value of the match between the current white LED. Constant voltage drive with high current-limiting resistor value, you can get a good current matching, but the negative impact efficiency. Conversely, the lower the current-limiting resistor value will provide a higher efficiency, but the matching effect of the white LED current (brightness) is poor.
The first generation of constant current drive with a constant current charge pump, these IC to detect white LED current limiting resistor. They may utilize the sensed current to adjust the first white LED forward current, its Yu Baiguang LED current limiting resistor, the current value will be matched with the first white LED current. Since the forward voltage between the white LED is not identical and therefore the accuracy of the current match is very limited. Applications requiring accurate current matching color LCD display, you can use the internal drive with constant current function, these drives provide accurate current matching between the white LED, without regard to its forward voltage.
White LED forward voltage is relatively high, the latest technology trend is to white LED forward voltage is decreased to 3V or less. Its nominal voltage value of 3. 6V, white LED forward voltage is lower than 3V 2. 7 ~ 4. 2V, by a single lithium-ion battery voltage range can be lithium-ion battery directly drive a white LED circuit ( without boost), thereby reducing the number of parts and cost.
Unlike traditional white LED driver IC, the white LED driver using active matching techniques in order to achieve a constant brightness white LED with a built-in digital, analog and PWM control unit to adjust the white LED brightness. The Fairchild the latest FAN5608LED of the drive to integrate the brightness control mode (digital, analog, PWM), and supports a special configuration program. It uses two constant current source drives two white LED series branch, each SMD LED series branch has a separate brightness control, 4 white LEDs in series for each white LED series support on the road, so as to meet the driving eight white LED's requirements.
Poor white LED's forward voltage drop match early white LED driver should match the current limiting resistor, to compensate for the forward voltage differences, in order to ensure white LED brightness consistency. However, the newly developed white LED driver IC supply voltage can not maintain a constant brightness. Upgrade and adjust the battery voltage driver IC can be open or closed loop controller, charge pump or inductive converter with voltage or current output.
In most applications, the white LED is in parallel or in series together. However, in individual cases, it also can be mixed in series and parallel configurations. LED connection in series or in parallel or hybrid depending on the needs of the application, each configuration has its own advantages and shortcomings.
1. The series. The white LED has a the similar diode forward voltage and current characteristics. Since the white LED brightness almost entirely by the current control, therefore, just use the same or match the current, two white LED light can be obtained the same brightness, without having to consider the difference of the forward voltage. White LED connected in series to ensure that its current is the same, therefore all white LED brightness is consistent.
2. The parallel. Most parallel white LED configurations use a constant voltage or constant current drive, and the drive is used depends on the specific application requirements. Parallel white LED driver in a constant voltage topology is very simple, the drive can be open-loop voltage output switching DC / DC regulator converter. Each white LED series with a current limiting resistor to set the current value of the match between the current white LED. Constant voltage drive with high current-limiting resistor value, you can get a good current matching, but the negative impact efficiency. Conversely, the lower the current-limiting resistor value will provide a higher efficiency, but the matching effect of the white LED current (brightness) is poor.
The first generation of constant current drive with a constant current charge pump, these IC to detect white LED current limiting resistor. They may utilize the sensed current to adjust the first white LED forward current, its Yu Baiguang LED current limiting resistor, the current value will be matched with the first white LED current. Since the forward voltage between the white LED is not identical and therefore the accuracy of the current match is very limited. Applications requiring accurate current matching color LCD display, you can use the internal drive with constant current function, these drives provide accurate current matching between the white LED, without regard to its forward voltage.
White LED forward voltage is relatively high, the latest technology trend is to white LED forward voltage is decreased to 3V or less. Its nominal voltage value of 3. 6V, white LED forward voltage is lower than 3V 2. 7 ~ 4. 2V, by a single lithium-ion battery voltage range can be lithium-ion battery directly drive a white LED circuit ( without boost), thereby reducing the number of parts and cost.
Unlike traditional white LED driver IC, the white LED driver using active matching techniques in order to achieve a constant brightness white LED with a built-in digital, analog and PWM control unit to adjust the white LED brightness. The Fairchild the latest FAN5608LED of the drive to integrate the brightness control mode (digital, analog, PWM), and supports a special configuration program. It uses two constant current source drives two white LED series branch, each SMD LED series branch has a separate brightness control, 4 white LEDs in series for each white LED series support on the road, so as to meet the driving eight white LED's requirements.
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