Power Electronics Technology Conference 2007 Specify Saturation Properties of Ferrite Cores to Prevent Field Failure George Orenchak

Power Electronics Technology Conference 2007 Reasons Why Saturation Properties are Seldom Specified Miss-perception that saturation data published in suppliers catalogs is sufficient Miss-perception that saturation properties are difficult & expensive to measure Miss-perception that saturation is difficult to quantify Miss-perception that saturation is not a critical characteristics

Power Electronics Technology Conference 2007 Purpose of This Presentation To explain the magnetic saturation property of ferrite cores Stress importance of specifying saturation Offer simple, inexpensive, measurement for verifying that your ferrite core is not saturated Offer method for determining the saturation specification for a ferrite core

Power Electronics Technology Conference 2007 A Magnetic Material is Saturated When it Reaches the Limit of Flux Lines it Can Efficiently Conduct

Power Electronics Technology Conference 2007 Result of Saturating Your Core Core no longer conducts flux lines efficiently Effective Permeability and component inductance sharply decreases often causing circuit currents to escalate Core loss increases exponentially and power is dissipated in the form of heat. Thermal runaway can occur

Power Electronics Technology Conference 2007 Gapping a Core Does Not Change the Saturation Flux Density

Power Electronics Technology Conference 2007

Change Effective Permeability and Magnetizing Force (Hdc) to Core Size Specific Units of Measure Inductance Index (A L ) = Lair * µ e A L = (0.004 * ¶ * A e *10 -6 / L e ) * µ e Ampere Turns (NI dc ) = H dc * L e / (0.4 * ¶)

Power Electronics Technology Conference 2007

Wayne Kerr Model 3255B Paired with 3265/25A DC Bias Unit

Power Electronics Technology Conference 2007 Example of the Excel Spread sheet

Power Electronics Technology Conference 2007 Center Leg vs. Distributed Gap

Power Electronics Technology Conference 2007 Reality vs. Theory Issues Non-uniform cross sectional core area Use the minimum cross sectional area Fringing flux issues Differences in gapping method and coil construction may influence results

Power Electronics Technology Conference 2007 Prevent Field Failure Specify a minimum inductance with a specific superimposed dc bias current on all your ferrite cores and components Use TSC Ferrite International’s excel spread sheet to easily determine the dc bias current a particular TSC Ferrite core should handle