Specify Saturation Properties of Ferrite Cores to Prevent
- Slides: 14
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
Power Electronics Technology Conference 2007
Change Effective Permeability and Magnetizing Force (Hdc) to Core Size Specific Units of Measure • Inductance Index (AL) = Lair * µe AL = (0. 004 * ¶ * Ae *10 -6 / Le) * µe • Ampere Turns (NIdc) = Hdc * Le / (0. 4 * ¶) Power Electronics Technology Conference 2007
Power Electronics Technology Conference 2007
Wayne Kerr Model 3255 B Paired with 3265/25 A 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 Power Electronics Technology Conference 2007