| 积层陶瓷电容 (MLCC) |
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MLCC 特性曲线
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Temperature Coefficient
Class 1 (Temperature Compensation Series)
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Class 2 (High Dielectric Constant Series)
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DC Voltage Coefficient
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Aging Rate
The capacitance and dissipation factor of class 2 capactiors decreases with time. It is known as 'again' that follows a logarithmic low and expressed in terms of an aging constant. Aging is caused by a gradual re-alignment of the crystalline structure of the ceramic. The aging constant is defined as the percentage loss of capacitance at a 'time decade'. The law of capacitance aging is expressed as following equation:
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Ct2=Ct1 x (1-k x log10(t2/t1))
Ct1: Capacitance after t1 hours of start aging.
Ct2: Capacitance after t2 hours of start aging.
K: aging constant (capacitance decrease per decade)
t1, t2: time in hours from start of aging.
A typical curve of aging rate is shown in following figure.
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When heating the capacitors above Curie temperature (130°C~150°C) the capacitance can be re-new. So capacitance of 2 capacitors will be complete de-aged by soldering process; subsequently a new aging process begins.
Because of aging, it is specified an age for measurement to meet the prescribed tolerance for class 2 capacitors. Normally, 1000 hours (t2=1000 hrs) is defined.
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