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large capacitance MLCC using for LED drive
Oct 09, 2016

Case of LED drive for reference

Aluminum electrolytic capacitor hashigh mlcc  ceamic chip capacitor been the main component in the recent past for its low cost, but its service life is short which usually be 105 degree 2000h.


Some famous manufacturers abroad claim that they
have developed aluminum electrolytic reach 10,000h at 105 degree, but it is useless compared with the LED service
life of 100,000h. The main reason is the hydration reaction of the internal material electrolyte in electrolytic capacitor, the negative electrode foil surface of aluminum electrolytic capacitor, the negative electrode foil surface of electrolytic capacitor will form aluminum hydrate with very high resistivity for its long term high temperature conditions. The resistance of negative electrode foil grows bigger with the aluminum hydrate increasing, under the ripple current pressure, the heat of electrolytic capacitor becomes more intense and then lead the final result of aluminum electrolytic capacitors early failure and crack. Picture 1 as below.



图1The famous exploding events of electrolytic capacitor is Dell computer made compensation of USD 30 million to clients for the aluminum electrolytic capacitor exploding on computer motherboard, this aluminum electrolytic capacitor manufacturer payed for USD 2 billion to Dell.Samsung video terminal has aluminum electrolytic capacitor explosion in England World Cup period, which caused extremely negative social influence, economic losses and social risks.


To break through this technical hurdle, in the recent years past, some one in the industry proposed “No aluminum electrolytic capacitor LED driving scheme”. it seems solved the problem, but it doesn’t. The main reason is this scheme make rectifier output voltage ripple increased (or ripple current). When LED worked on high or normal power conditions, it will cause periodic over current on power frequency( power frequency in China is 50HZ, and in USA Japan is 60HZ). See picture 2 below.



无标题When LED current at 700mA, the corresponding forward voltage would be 3.4V, assume the LED peak voltage is 0.25V( the actual is usually higher), then the current through LED exceeds the 900mA ratings, which finally causes the short service life of LED.

If we set the electric current be less than

the rated current, the loss will be increased, it may leads the bad phenomena like LED flashe seriously, lumen or brightness shadowy just like fluorescent lamp.


With the continuous progress of multilayer ceramic capacitor technology, Jinpei Co, made much progress with its unique advanced technology process. Add rare earth metal oxide modified on the basic of D50 100 manometers TIPS BaTiO3, combines the original sandwich laminate structure making the high reliable X7R/X5R、NPO/COG ceramic powder, successfully developed UPµF class high capacity chip, ceramic capacitor X7R/X5R material and capacity 100UF 220UF 330UF 470UF,NPO/COG 0.1UF 2000V…. Size 0201 0402 0603 0805 1206 1812 2220……and high frequency chip multilayer ceramic capacitor. It is the originate technology in domestic and abroad, breaking the hurdle of capacity limit of multilayer ceramic capacitor than traditional electrolytic capacitor and saved 45% of installation space.


Paralleling a 100uF and a 1uF chip multilayer ceramic capacitor, the ESR is 3mΩ much lower than the previous 16mΩ. Some bypass capacitors in high-frequency big power supply circuit will need alternating load current that caused by load and bigger bypass, it requires the bypass capacitor with very low ESR and ESL, among various of capacitors, the chip multilayer ceramic capacitor has low ESL which is just several Henry. The scientific

standard to choose a high frequency rectification capacitor is based on the ripple current it bears, while the value ripple current bears depends on the ESR value of the capacitor(the smaller the ESR, the bigger value ripple current bears). A standard LED driving power uses aluminum electrolytic capacitor with a ESR value of 350 MΩ and under 0.65A ripple current, A standard LED driving power uses large capacity chip multilayer ceramic capacitor with ESR 10~30 MΩ and under 2.5~4.0A ripple current. Again, at the load power supply terminal access 47uF electrolytic capacitor, the peak value of ripple current is 25mVp-p,when access to 4.7uF high-capacity ceramic capacitor, it turns to 5Mv. See picture 3.


Thus it can be seen, high-capacity chip multilayer ceramic capacitor applied on LED drive and the complete machine power supply, has great significance to improve its service life and overall performance.

图3

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