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Basic Electronics Ninth Edition Grob Schultz

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1 Basic Electronics Ninth Edition Grob Schultz
©2002 The McGraw-Hill Companies

2 Basic Electronics Magnetic Units 14 Ninth Edition CHAPTER
©2003 The McGraw-Hill Companies

3 Topics Covered in Chapter 14
Ampere-turns of Magnetomotive Force (mmf) Field Intensity (H) Permeability (m) B-H Magnetization Curve

4 Topics Covered in Chapter 14 (continued)
Magnetic Hysteresis Ohm's Law for Magnetic Circuits Relations between Magnetic Units Comparison of Magnetic and Electric Fields

5 Ampere -Turns Ampere-turns = I ´ N
I ´ N specifies the amount of magnetizing force or magnetic potential (mmf). I is the amount of current flowing through N turns of wire.

6 Magnetomotive Force (A•t)
Ampere-turns = I x N.

7 Field Intensity (H) Equation: H = mmf/length
Units: A·t/m ampere-turns per meter Shorter magnetic circuits produce a greater field intensity.

8 The field intensity in the core is inversely related to length.
Field Intensity (H) length The field intensity in the core is inversely related to length. H = A·t/m (ampere-turns per meter)

9 B-H Magnetization Curve
B meter 0.5 0.4 Saturation B in Teslas 0.3 0.2 0.1 Soft iron k 2k 3k 4k 5k H in A•t/m

10 Hysteresis Loop BR is due to retentivity. (Note that H = 0
but B > 0.) + B + Bmax HC is the coercive force. (that needed to make B = 0) + BR - HC - H + H + HC - BR - Bmax - B

11 Demagnetization (Also Called Degaussing)
BR is reduced to zero.

12 Hysteresis Curve When Retentivity is Very Low
+ B + Bmax - H + H - Bmax - B

13 Permeability (m) Permeability is a measure of the ability to concentrate magnetic fields. Equation: m = B/H Unit: T A t m × / teslas per ampere-turn per meter

14 Permeability drops drastically at saturation.
+ Bmax Slope of B/H is large Slope of B/H is small - H + H - Bmax - B

15 Reluctance Reluctance is the opposition to flux. It is comparable with resistance in an electrical circuit. Equation: Â = mmf /f Units: A·t/Wb ampere-turns per weber

16 Permeance Permeance is comparable with conductance in an electrical circuit (G = 1/R). Equation: r = 1/Â Units: Wb/A·t webers per ampere-turn

17 Ohm’s Law for Electrical and Magnetic Circuits
Electrical circuits: I = V/R Magnetic circuits: f = mmf /Â

18 Increasing reluctance decreases flux.
Adding an air-gap increases the reluctance. I As  increases,  decreases.

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