Inductor Selection: Buck Converters
Switch
Buck
Inductor
Inductor Selection: Boost Converters
Boost
Inductor
Diode
12V
Input
Voltage
Freewheeling
Diode
Output
Cap
5V
Output
Voltage
5V
Input
Voltage
Switch
Output
Cap
12V
Output
Voltage
Figure 2:
Buck Inductor Example
Figure 3:
Boost Inductor Example
Figure 2 Application Parameters:
• Switching frequency= 250kHz
• Input voltage range= 12V±10%
• Max ripple current = 220mA
• Output Voltage= 5.0V
Step 1. Calculate the Duty Cycle
• Vo = output voltage
• Vi = Max input voltage
• D = Vo / Vi
• D = 5/13.2 = 0.379
Step 2. Calculate the Voltage Across the Inductance
• V1 = Vi-Vo (Switch on)
• V1 = 13.2 - 5 = 8.2V
• V1 = -Vo (Switch off)
• V1 = - Vo = - 5V
Step 3. Calculate the Required Inductance
• L = Vl.dt/di
• L = (8.2 x 0.379/250 x 10
3
)/0.22
• L = 56μH
Figure 3 Application Parameters:
• Switching frequency= 100kHz
• Input voltage range= 4.5-5.5V
• Max ripple current = 100mA
• Output Voltage= 12.0V
Step 1. Calculate the Duty Cycle:
• Vo= output voltage
• Vi = Max input voltage
• D = 1 - (Vi / Vo)
• D = 1 – (5.5/12.0) = 0.542
Step 2. Calculating the voltage across the inductance
• V1 = Vi (Switch on)
• V1 = 5.5V
• V1 = Vo – Vi (Switch off)
• V1 = 12 – 5.5 = 6.5V
Step 3. Calculating the required inductance
• L = Vl.dt/di
• L= (5.5 x 0.542/100 x 10
3
)/0.1
• L= 298μH
Typical Applications Using Inductors for Switching Regulators
Industrial Test Equipment
Media Players
Digital Cameras
Laptop Computers
Backlight Displays
Mobile Phones
COOPER [ COOPER BUSSMANN, INC. ]
