Inductor Selection: Buck Converters
Inductor Selection: Boost Converters
Boost
Buck
Inductor
Diode
Inductor
Switch
5V
Output
Voltage
12V
Input
Voltage
Freewheeling
Diode
Output
Cap
12V
Output
Voltage
5V
Input
Voltage
Output
Cap
Switch
Figure 2:
Buck Inductor Example
Figure 3:
Boost Inductor Example
Figure 2 Application Parameters:
•Switching frequency= 250kHz
Figure 3 Application Parameters:
•Switching frequency= 100kHz
•Input voltage range= 12V 10%
•Max ripple current = 220mA
•Output Voltage= 5.0V
•Input voltage range= 4.5-5.5V
•Max ripple current = 100mA
•Output Voltage= 12.0V
Step 1. Calculate the Duty Cycle
Step 1. Calculate the Duty Cycle:
•V = output voltage
•V = output voltage
o
o
•V = Max input voltage
i
•V = Max input voltage
i
•D = 1 - (V / V )
•D = V / V
i
o
o
i
•D = 1 – (5.5/12.0) = 0.542
•D = 5/13.2 = 0.379
Step 2. Calculating the voltage across the inductancce
•V = V (Switch on)
Step 2. Calculate the Voltage Across the Inductance
•V = V -V (Switch on)
1
i
1
i o
•V = 5.5V
1
•V = 13.2 - 5 = 8.2V
1
•V = V – V (Switch off)
•V = -V (Switch off)
1
o
i
1
o
•V = 12 – 5.5 = 6.5V
1
•V = - V = - 5V
1
o
Step 3. Calculating the required inductance
Step 3. Calculate the Required Inductance
•L = V .dt/di
•L = V .dt/di
l
l
•L= (5.5 x 0.542/100 x 103)/0.1
•L = (8.2 x 0.379/250 x 103)/0.22
•L= 298μH
•L = 56μH
Typical Applications Using Inductors for Switching Regulators
Industrial Test Equipment
Media Players
Digital Cameras
Laptop Computers
Backlight Displays
Mobile Phones
COOPER [ COOPER BUSSMANN, INC. ]
