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SD3814-100-R 参数 Datasheet PDF下载

SD3814-100-R图片预览
型号: SD3814-100-R
PDF下载: 下载PDF文件 查看货源
内容描述: 开关稳压器 [Switching Regulators]
分类和应用: 稳压器开关
文件页数/大小: 4 页 / 373 K
品牌: COOPER [ COOPER BUSSMANN, INC. ]
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Inductor Selection for Switching Regulators
Introduction/Basic Operation
In switching regulator applications the inductor is used as an energy
storage device. When the semiconductor switch is on the current in the
inductor ramps up and energy is stored. When the switch turns off energy
is released into the load. The amount of energy stored is calculated by the
formula
Energy = �½L.I²
(Joules), where:
• L is the inductance in Henrys
• I is the peak value of inductor current
The amount by which the current changes during a switching cycle is
known as the ripple current. Ripple current is defined as Vl = L.di/dt:
• Vl is the voltage across the inductor
• di is the ripple current
• dt is the duration for which the voltage is applied
I load
dI
I inductor
0
1
2
ESR
V out
Figure 1:
Buck Inductor
Inductor current is made up of AC and DC components (Figure 1). The AC
component is high frequency and will flow through the output capacitor
because it has a low HF impedance. A ripple voltage is produced due to
the capacitor ‘equivalent series resistance’ (ESR) that will appear at the
output of the switching regulator. This ripple voltage needs to be
sufficiently low as not to effect the operation of the circuit the regulator is
supplying, normally in the order of 10-500mVpk-pk.
Selecting the correct ripple current impacts the size of the inductor and
output capacitor. The capacitor needs to have a sufficiently high ripple
current rating or it will overheat and dry out. To achieve a good
compromise between inductor and capacitor size a ripple current value of
10-30% of maximum inductor current should be chosen. The current in
the inductor will be continuous for output currents greater that 5-15% of
full load.
The following parameters need to be defined or calculated to select an
inductor:
• Maximum input voltage
• Output voltage
• Switching frequency
• Maximum ripple current
SD3814
• Duty cycle