Change the output capacitor in step-down DC-DC converter is MLCC

 

Graph the 7 basic circuit that are converter of the relatively commonly used step-down in waiting for electronic equipment as POL converter small-sized DC-DC. The main circuit of converter gets IC is changed, pass presswork capacitor and inductor are received outside circuit board (also have inside buy product) before be located in IC paragraph capacitor calls input capacitor (Cin) , after be located in paragraph capacitor calls output capacitor (Cout) . The output capacitor of DC-DC converter makes output voltage flowing through accumulating charge change, the moire part that has to will communicate at the same time is released to side of ground wire layer, and the action its eliminate.

 

The output capacitor character in step-down DC-DC converter is compared

 

 

Because the ESR of MLCC is inferior, because this is moire voltage is lesser, oneself are calorific less.

 

The condition is narrated before the basis, the common aluminium that is 22μF to static Zuo capacity electroanalysises capacitor, Tantalum electroanalysises high polymer of sex of capacitor, function is aluminous electroanalysis capacitor and MLCC compared voltage of output electric current and output respectively.

 

ESR and the moire tension that cause oneself to give out heat from it is to small order greatly: Common aluminium electroanalysises capacitor ＞ Tantalum electroanalysises high polymer of sex of capacitor ＞ function is aluminous electroanalysis capacitor ＞ MLCC.

 

Functional sex high polymer is aluminous electroanalysis capacitor is the product that realizes conductivity polymer low ESR as electrolyte, electroanalysis with common aluminium capacitor photograph is compared, moire voltage is remarkable decrescent, but its figure is greater, the price is higher also.

 

 

The impedance of each capacitor – frequency character, ESR- frequency character is shown as follows.

 

 

ESR jumps over small capacitor, can restrain moire voltage smaller. If undermentioned chart place is shown, the characteristic of MLCC depends on ESR minimum, only left and right sides of amount to MmΩ . Accordingly, use MLCC changes electroanalysis capacitor aux will be able to produces admirable show quite.

 

 

Stick a capacitance good point: Restrain moire, high reliability, macrobian life to change

 

ESR is taller electroanalysis capacitor can bring about him to give out heat because of moire electric current, shorten thereby life.

 

The ESR of MLCC than electroanalysising capacitor reduces a quantity to reach two digit, dependability rose while implementation grows life.

 

 

Stick a capacitance to use a note:

 

Series of tall dielectric constant notices to bring to bear on please the capacity that voltage creates changes

 

Even if exceedingly good capacitor MLCC also has a weak point. MLCC can differ because of the voltage that bring to bear on and bring about electrostatic capacity to produce change. Those who bring to bear on is character of DC bias voltage is called when volts d.c. () of volts d.c. character. The change of electrostatic capacity (depend on each other of DC bias voltage) in series of low dielectric constant (can appear scarcely in phyletic 1) , and can be in series of tall dielectric constant (appear in the capacitor of pottery and porcelain of phyletic 2) .

 

Its reason depends on, the ferroelectric material that what series of tall dielectric constant uses is initiative polarization (the) such as BaTiO3. Accordingly, bring to bear on when volts d.c. undertakes use, the character that considers dielectric when the choice please, use voltage reachs the element such as compression. In the meantime, capacitor size is smaller, the decrement of electrostatic capacity can be jumped over big. Choosing a capacity is, also need to consider character of DC bias voltage.

 

 

The MLCC existence of series of tall dielectric constant passes ※ temperature change and bring to bear on the weakness that volts d.c. can make electrostatic capacity drops () of character of temperature character, DC bias voltage. In the meantime, because its have extremely low ESR, because this can create the problem of unusual vibration and antiresonance instead, because this needs an attention when change.