| 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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