Inductors are devices that store and convert energy. A BH loop characterizes the useful region of operation of a magnetic component. When a gap is introduced into the core either discretely, as in a ferrite or distributed, as in a powder core, the ability of the device to store energy is greatly enhanced, from the region of 0.2 – 2.0 Oersteds for an ungapped core set to 100 – 1000 Oersteds for a gapped core by shearing over the BH loop (to learn more about powder core BH Loops, view our white paper). Gaps in inductors are introduced for the purposes of: controlling inductance, reducing inductance, maintaining inductance under load and reducing the change in inductance due to shifting currents or temperatures. Ferrite inductors have the advantages of low cost, low losses, flexible geometries, good shielding properties and excellent tolerance capabilities, often in the range of ±3%. Pot cores that have tuning capabilities can be adjusted to an exact AL when this is required to balance a capacitor or for other precise applications.
In a power transformer design there are two main goals to keep in mind--keeping the core out of saturation and minimizing core losses. Materials for transformers typically have high permeability, usually ferrites or tape wound cores. The characteristics to consider when choosing between tape wound cores and ferrites are: Frequency and temperature of operation, and unit cost, size and shape. Ferrite cores offer the benefits of low losses, low cost and a wide variety of available shapes and sizes. Pot cores offer the advantage of protective shielding which can be important in EMI/RFI sensitive designs. Planar E cores offer ease of assembly, consistent results and a low profile. Ferrites are typically considered for use at frequencies of 10 kHz and above. Above 20 kHz the ferrite design is typically loss-limited while below 20 kHz the design is typically limited by the flux capacity of the unit. Tape wound cores have higher B max, saturation flux density, so the overall design can be smaller.
Designing with Magnetics Powder Cores
- View the Powder Core Calculations page for a list of common calculations used by magnetics designers: Winding Factor, Mean Length of Turn (MLT), DC Resistance (DCR), Wound Coil Dimensions, and Temperature Rise.
- View the Core Loss Calculation page for a step-by-step method to calculate losses generated by powder cores under certain conditions.
Block Structures and Products for High Current Applications
Rapid expansion in the solar and wind power conversion, hybrid vehicle, and UPS markets has increased the demand for high current (100-300 amps) inductors. For many high-current applications the limiting factor is not necessarily the material's ability to provide enough inductance at DC Bias, but rather it is the ability to fit enough turns of the heavy wire or foil to provide the necessary inductance. Magnetics offersa number of larger E cores and U cores that can accommodate both larger wire sizes and greater amounts of wire; however, in come cases a larger shape is required to support inductance at currents greater than 100 amps. Magnetics blocks can be arranged to support this inductance requirement. Kool Mu and XFlux blocks come in a variety of sizes and shapes for flexibility and customization of a design. New sizes can also be tooled. Contact Magnetics for more information.