电感电流纹波率和电感量的关系
电感电流方程
?I=V ?t/L
表达式变换为
?I?Et/LuH其中Et为伏微秒数
电感电流纹波率定义为
r??I/IL?Et/LuHIL
进一步得到
r?EtV?DV?(1?D)（ =OFF，CCM模式成立）公式一 ?ONL?ILL?IL?fL?IL?f其中为D为电感通断点的时间占空比，此公式对于所有拓扑结构都有效
以上变换得到公式
L?VON?D
r?IL?f任何场合r值选择约为0.3-0.5之间
****************************应用实例buck电感规格选择***************** MP1482 datasheet…………………….
The inductor is required to supply constantcurrent to the output load while being driven bythe switched input voltage. A larger valueinductor will result in less ripple current that willresult in lower output ripple voltage. However,the larger value inductor will have a largerphysical size, higher series resistance, and/orlower saturation current. A good rule fordetermining the inductance to use is to allowthe peak-to-peak ripple current in the inductorto be approximately 30% of the maximumswitch current limit. Also, make sure that thepeak inductor current is below the maximumswitch current limit. The inductance value canbe calculated by:
Where VOUT is the output voltage, VIN is theinput voltage, fsis the switching frequency, andΔIL is the peak-to-peak inductor ripple current.
Choose an inductor that will not saturate underthe maximum inductor peak current. The peakinductor current can be calculated by:
Where ILOAD is the load current.The choice of which style inductor to use mainlydepends on the price vs. size requirements andany EMI requirements. 分析如下
对于buck电路，有以下公式 Ton阶段
Vout=Vin-Von
Toff阶段
Vout=Voff
Buck电路的占空比
D=Ton/(Ton+Toff)=Vout/Vin
根据公式一，相应的电感公式为
L?(Vin?Vout)?D
r?IL?f(Vout)?(1?D)
r?IL?f和L?以上两个公式实际上可以相互转换，以后一个公式计算得到：
L???(Vout)?(1?D)r?IL?fVoutVout?(1?)
r?IL?fVinVoutVout?(1?)?I?fVin显然这里的结构和datasheet中是相同的
对于负载峰值电流必须小于电感的饱和电流，这点在选择电感的规格尤其重要
一般来说如果buck电路实际负载电流达到DCDC标称输出电流，那么功率电感的饱和电流最好选择1.5-2倍于负载电流
纹波电流和电感量呈反比关系——大的电感纹波电流小
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r的最佳值问题