Circuits II EE221 Unit 9 Instructor: Kevin D. Donohue

1. Circuits IIEE221Unit 9Instructor: Kevin D. Donohue Mutual Inductance, Energy in Magnetically Coupled Circuits, Analysis of Mutual Inductance Circuits

2. Mutual Inductance Coils with current flowing in them emit magnetic energy that induce voltages in other coils in close proximity. The effects of the magnetic link between these circuits is called mutual inductance. Show that current i1 in first coil induces voltage v2 in second coil of the form:

3. Mutual Inductance Dot Convention The geometry of the coil and flux paths are expressed in the dot convention below. This notation is important for applying circuit laws for analysis.

4. M I1 I2 + V1 - + V2 - L1 L2 Dot Notation for KVL M If both currents are either entering or leaving the dot then the self and mutual induced voltage will have the same sign. If one current (loop direction) enters the dot and the other current leaves the dot, then the self and mutual induced voltage will have opposing signs. I1 I2 + V1 - + V2 - L1 L2

5. M I1 I2 + V1 - + V2 - L1 L2 Equivalent Circuits Example M Convert the Mutual Inductance components to an equivalent circuit using current controlled voltage sources. I1 I2 + V1 - + V2 - L1 L2

6. Examples • Find vo(t), given vi(t) = 2cos(4t) V. • Show vo(t) = 0.4851cos(4t-14º) V 1H 4 + vi(t) - vi(t) 2 1H 2H

7. Examples • Find Norton equivalent circuit wrtab • Show Ith= A Zth=  20  j20  a j10  j5  b

8. Examples • Find equivalent inductance wrtab • Show Leq= H a 1 H 6 H 2 H 4 H 5 H 1 H b