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After determining the optimal size of the total gap in the ferrite
material, we optimized the design by reducing the losses in
the inductor based on the understanding that the fringing flux
(radiated magnetic field) from the gap in the core can cause
eddy currents in copper. This, in turn, can cause localized
joule loss in the copper coil. The average current in the boost
inductor will track the input voltage signal in relative shape and
phase during the cycle.
Significant Loss Reductions Achieved
Using Bourns' gapped ferrite construction, a very efficient,
high-density design was achieved with up to 3.6kW
throughput per channel, with the capability to store 125mJ
in each cycle at full load. Our PFC simulations supported our
determination of the optimum gap required to store energy
and prevent saturation. Plus, we were able to establish that
the main source of copper power losses was AC resistance
leading to the conclusion that our design should have a
maximum AC resistance specification target of 750mΩ at
125kHz and 100°C. To verify, analyze, and optimize the boost
inductor design, we utilized FEA software.
The Bourns
®
boost inductor can reduce AC losses by as
much as 90 percent depending upon the application. The
keys to this reduction were decreasing the gap size and
increasing the number of gaps in the center leg of the inductor.
Our tests showed that AC resistance reduced from 5.5Ω
with a single-gap inductor to just 0.616Ω with our three-gap
design in the tested application. The result of loss reduction
in AC resistance was a significant reduction in AC copper
losses -- from 20W down to a scant 1.8W per channel. Since
it produces less heat, the Bourns
®
boost inductor requires
less cooling while delivering the added benefit of reduced
EMI. All combined, these advantages help to optimize PFC
stage designs contributing to overall OBC efficiency gains that
further propel electric vehicle market growth.
Key Features:
• Sulfur-resistant design
(ASTM B-809)
• Power rating up to 2W at +70°C
• High power surge withstanding
Key Features:
• AEC-Q200 compliant
• Effective magnetic shielding
• Lower radiation than
non-shielded inductors
CRM-A & CRS-A AEC-Q200 Compliant
High Power Thick Film Resistors
SRN Product Family Automotive
Semi-Shielded Power Inductors
mouser.com/new/bourns/bourns-
high-power-aec-q200-resistors/
mouser.com/new/bourns/
bourns-srn-automotive-inductors/
Figure 2: This simulation graph illustrates the inductance and input current over 1 cycle. (Source: Bourns, Inc.)
