Ferrites - "The Most Important Properties" 1994 Soft Ferrite Users Conference. By : George Orenchak Ferrite International Company

Size: px

Start display at page:

Download "Ferrites - "The Most Important Properties" 1994 Soft Ferrite Users Conference. By : George Orenchak Ferrite International Company"

Oswin Haynes
6 years ago
Views:

1 Ferrites - "The Most Important Properties" 1994 Soft Ferrite Users Conference By : George Orenchak Ferrite International Company

2 Inductance - Electrical property that opposes any change in current because of a magnetic field. L = ((.4) (π) (N2) (Ae) (16)) / Le (in Henries) Material Permeability, core dimensions & number of turns all affect inductance and therefor affect component size Ae = effective cross sectional area Le = effective magnetic path length Inductance Index Al is the Inductance per unit turn in nh/n2 N = turns on coil. Ferrites - "The Most Important Properties" Slide 1

3 B ua Bs Hysteresis Curve B = Magnetic Flux Density Flux per unit area induced by a field s Br H = Magnetizing Force The externally applied force that indu flux in a magnetic material ui u = B / H = Permeability Initial Permeability at low amplitudes - H - Hc Hc H Amplitude Permeability at high amplit Bsat = Saturation Flux Density The value of magnetic flux density at -B - Br Br = Residual Induction The magnetic Induction remaining in material after the magnetizing force ( removed - B Ferrites - "The Most Important Properties" Slide 2

4 Permeability TSF-5 TSF-77 TSF-84 Initial Permeability vs. Temperature Temperature in Centigrade Permeability varies with temperature and drops to unity above the curie temperature. Ferrites - "The Most Important Properties" Slide 3

5 Permeability Permeability vs. Flux Density TSF-77 material 25 centigrade 1 centigrade Flux Density in Gauss Permeability varies with Flux Density and drops to unity when saturated. Soft Ferrite materials saturate sooner at elevated temperatures. Ferrites - "The Most Important Properties" Slide 4

6 Saturation Flux Density - The value of magnetic flux density at saturation. A materials maximum magnetic induction. B = (Erms)(18) / (4.44)(f)(N)(Ae) Flux Density (gauss) Saturation Flux Density vs. Temperature TSF-77 material 15 oersteds Saturation Flux Density decreases with increasing temperature. Often a material's Saturation Flux Density is a constraint on the minimum core size. f = frequency N= turns Ae = effective core area Temperature in Centigrade Ferrites - "The Most Important Properties" Slide 5

7 -H B ungapped Gapp H The hysteresis loop shears over with increasing gap depths. The gapped structure results in lower effective permeabilities but requires more magnetizing force to saturate the core. Gapped ungapped -B Ferrites - "The Most Important Properties" Slide 6

8 Inductance Index AL vs. Gap Depth AL value TSF E core Gap Depth Inductance decays exponentially as the air gap increases. The slope is steep for small gaps which have large AL values. For this reason larger tolerances are needed compared to the AL tolerances for deep gaps that have shallow slopes and small AL values. AL=(4πµAeAg)/(µAeLe)+Ag(Le-LG) times (1+Lg/Square root Ae ln(2g/lg)) to account for fringing flux Ferrites - "The Most Important Properties" Slide 7

9 Inuctance Index (AL value) vs. Ampere Turns TSF-77 material.5" gap.1" gap.15" gap Inductance rolls-off as the material saturates. Small gaps (Large AL values) saturate sooner than large gaps (small AL values) AL value Ampere Turns Ferrites - "The Most Important Properties" Slide 8

10 Losses Loss Factor - Figure of merit of a material at low levels of magnetizing force ( Tan δ / µq = 1 / µq ) Core Loss - A measure of the efficiency of a material at high levels of magnetizing force. Dissipated energy in the form of heat. Often a materials core loss characteristics is a constraint on the minimum core size. Ferrites - "The Most Important Properties" Slide 9

11 Core loss vs. Temperature 25kH, 2 gauss mw/cc TSF-58 TSF-77 TSF Temperature in Centigrade A number of material grades have been designed so that their minimum core loss occurs at specific temperatures. Ferrites - "The Most Important Properties" Slide 1

12 Core loss vs. Flux Density TSF-77 material Core Loss increases exponentially with increasing Flux Density kh 1 kh 1 mw/cc Flux Density in gauss Ferrites - "The Most Important Properties" Slide 11

13 Core loss vs. Frequency TSF-77 material Core Loss increases exponetially with increasing frequency gauss 2 gauss 3 25 mw/cc Frequency in khz Ferrites - "The Most Important Properties" Slide 12

14 % change in permeability Disaccommodation Inductance vs. Time TSF-77 material Time in minutes Disaccomodation is the variation of permeability with time. Mechanical, magnetic or thermal disturbances cause the initial permeability to be raised to an unstable value from which it returns as a function of time. This process is indefinitely repeatable. Ferrites - "The Most Important Properties" Slide 13

15 Ferrite Material Constants Specific Heat.25 cal / g / c Thermal Conductivity 1 x 1-3 cal / sec / cm / c Coefficient of Linear Expansion 8 to 1 x 1-6 / c Compressive Strength 6 x 13 lbs / in2 Young's Modulus 18 x 13 lbs / in2 Hardness (Knoop) 65 Density 4.6 to 4.8 gm / cm3 Ferrites - "The Most Important Properties" Slide 14

Definitions of Terminology in Magnetics

Definitions of Terminology in Magnetics Ag Area of the air gap, or the cross sectional area of the air gap perpendicular to the flux path, is the average cross sectional area of that portion of the air