2 DEFINEDWhen a length of wire is formed onto a coil, it becomes a basic inductor
3 DEFINEDMagnetic lines of force around each loop in the winding of the coil effectively add to the lines of force around the adjoining loops, forming a strong electromagnetic field within and around the coil
4 DEFINEDA inductor is a device which stores energy in a magnetic field
5 DEFINEDInductor consists of a coil of wire, usually around a metallic or ferromagnetic core which creates an electromagnet
6 DEFINEDA current through an inductor creates a magnetic field around the coil which resists any changes in current
7 DEFINEDThe unit of inductance is the henry (H), defined as the inductance when one ampere per Second through the coil, induces one volt across the coil
8 DEFINEDThe unit of inductance is the henry (H), defined as the inductance when one ampere per Second through the coil, induces one volt across the coilN= Number of Turnsµ = dielectric constantA = cross-sectional area of the coill = length of the coil
9 DEFINED Schematic Symbols • A couple of symbols for the inductor are illustrated belowFixed InductorVariableSchematic Symbols
11 Rules of Inductor Behavior The current and voltage relationship in an inductor isIf the current isn’t changing, then the voltage change across the inductor is zero
12 Rules of Inductor Behavior An inductor is a short circuit to DCThe current through an inductor cannot change instantaneouslyIf current changed quickly, then we might have infinite voltageContradicts conservation of energy
13 Example Problem 1 What are the values of I and V, the current through and voltage across the inductor?The easier value to find is the voltage V. In this case, the current through the inductor isn’t changing, so the voltage must be 0 V. So V = 0 VIn DC conditions, an inductor acts like a short circuit – so we need to find the current through the resistor and it will be the same as the current through the inductor.
14 INDUCTOR CODE Use the color code guide in your handout as a means to Identify the value of the inductor.
15 RL TIME CONSTANTThe RL Time Constant is the time it takes, in a series resistor inductor circuit, for current to rise to 63.2% or fall to 36.8% of the peak voltage value of the circuit. When five of these time constants occur, the inductor will be fully discharged. The formula below can be used to predict this value.t = Time in secondsR = Resistance in OhmsL = Inductance in Henry’s
16 RL TIME CONSTANTThe current across an inductor cannot change instantaneously because a finite time is required to move charge from one point to another (limited by circuit resistance)t = Time in secondsR = Resistance in OhmsL = Inductance in Henry’s
17 RL TIME CONSTANT example With a 1kΩ resistor and a 1mH inductor are placed in series, what is the time constant of the circuit and how long will it take to fully discharge the inductor?Time Constant Calculationt =L/Rt=1mH/1kΩt =.001/1000t=1usDischarge Time = 1us x 5Full Charge Time = 5usTime for Discharge
18 RL TIME CONSTANT GRAPHIC REPRESENTATION The first cursor proves that at1us the current is 6.32VThe second cursor is showing that after 5 time constants the inductor represents a short circuit.
19 THEORYWhen a DC voltage source is connected to the inductor, voltage is maximum across the inductor because of the magnetic field caused by the maximum rate of change of current in the circuit.Note: at t = 0 secondsCurrent is 0 AmpsVoltage is Maximum Volts
20 THEORYAs the magnetic field “relaxes” due to the continuous DC, current begins to flow through the inductor. When this occurs, the voltage across the inductor begins to decrease and current through the inductor begins to rise.
21 THEORYEventually the inductor represents a short circuit. In an ideal inductor the voltage drop becomes 0 Volts and the current through the inductor becomes maximum.Note: at t = infinity secondsCurrent is Maximum AmpsVoltage is 0 Volts
22 Series and Parallel Inductors Inductors in SeriesWith several Inductors in series, they all act together to affect the current
23 Series and Parallel Inductors Inductors in ParallelWith several Inductors in parallel, we have to split the current, just like in resistors