Here for designing the resonant
inductor, the same method given in Reference [14] is followed. PFC LLC EVM [15] is considered as an design example.
Step 1: Specifications
Equation 65.
Equation 66.
Equation 67.
Step 2: Pick a core based on the maximum energy to be stored
Equation 68.
[Equation 10.100 in Reference 16]
Equation 69.
Equation 70.
Equation 71.
Equation 72.
Bm is chosen such that at
the operating frequency, core loss power density should be less than 150
mW/cm3 for natural convection cooling.
In general, suggested magnetic
materials for reducing core losses are 3C95, 3F4 from Ferroxcube (Ferroxcube Cores and Accessories)
and PC47, PC90, PC95 from TDK ( TDK Cores and Accessories).
Equation 73.
For this design, RM8 core with 3C95
material is selected. This core's effective cross section area
(Ferroxcube RM8 core data sheet) and
minimum winding area
(Ferroxcube RM8 bobbin data sheet).
Cores, Bobbin, Clamp can be obtained from following links: RM8 with 3C95, RM8 Bobbin, Clamp for RM8 Core.
Step
3: Wire Selection and Airgap calculation
Equation 74.
Equation 75.
Equation 76.
Equation 77.
[Equation 10.148 in Reference 16]
Equation 78.
Equation 79.
Equation 80.
Equation 81.
(
Litz Wire
Data from MWS Wire Industries)
Equation 82.
(Litz Wire
Data from MWS Wire Industries)
Equation 83.
Equation 84.
Equation 85.
Step 4: Copper Loss Calculation
Equation 86.
(Ferroxcube RM8 bobbin data
sheet)
Equation 87.
Equation 88.
(represented in Figure 1-37 as a
)
Equation 89.
Equation 90.
Equation 91.
Equation 92.
(Ferroxcube RM8 bobbin data
sheet)
Equation 93.
Equation 94.
[Table 10.1 in Reference 16]
[Equation 10.80 in Reference 9]
Equation 95.
[Equation 10.74 in Reference 9]
Equation 96.
[Equation 10.81 in Reference 9]
Equation 97.
[Equation 10.76 in Reference 9]
Equation 98.
[Equation 10.81 in Reference 9]
Equation 99.
Equation 100.
[Equation 10.73 in Reference 9]
Equation 101.
Equation 102.
[Equation 10.90 in Reference 9]
Equation 103.
Equation 104.
Equation 105.
where 0.1007 is AWG38 bare wire
diameter in mm [Table 10.1 in Reference 16].
Step 5: Flux Density and Core-Loss Calculation
Equation 106.
Equation 107.
(Use power loss calculator in the
Ferroxcube design tool for finding core loss of the material Core Loss Calculator)
Equation 108.
Equation 109.
Equation 110.
Step 6: Temperature Rise and Bobbin Fit
Calculations
Equation 111.
Equation 112.
Table 3-43
Equation 113.
[Equation 10.193 in Reference 16]
Equation 114.