1. ELECTRONICS TECHNOLOGY INDUCTANCE
2008JULY06
INDUCTANCE
Benchmark Companies Inc
PO Box
Aurora CO 80047
ELECTRONICS TECHNOLOGY INDUCTANCE

2. DEFINED
When a length of wire is formed onto a coil, it becomes a basic inductor

3. DEFINED
Magnetic 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. DEFINED
A inductor is a device which stores energy in a magnetic field

5. DEFINED
Inductor consists of a coil of wire, usually around a metallic or ferromagnetic core which creates an electromagnet

6. DEFINED
A current through an inductor creates a magnetic field around the coil which resists any changes in current

7. DEFINED
The 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. DEFINED
The 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
N= Number of Turns
µ = dielectric constant
A = cross-sectional area of the coil
l = length of the coil

9. DEFINED Schematic Symbols
• A couple of symbols for the inductor are illustrated below
Fixed Inductor
Variable
Schematic Symbols

10. INDUCTOR TYPES
Toroidal core inductor
Axial Lead
Variable Inductor

11. Rules of Inductor Behavior
The current and voltage relationship in an inductor is
If 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 DC
The current through an inductor cannot change instantaneously
If current changed quickly, then we might have infinite voltage
Contradicts 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 V
In 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 CONSTANT
The 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 seconds
R = Resistance in Ohms
L = Inductance in Henry’s

16. RL TIME CONSTANT
The 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 seconds
R = Resistance in Ohms
L = 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 Calculation
t =L/R
t=1mH/1kΩ
t =.001/1000
t=1us
Discharge Time = 1us x 5
Full Charge Time = 5us
Time for Discharge

18. RL TIME CONSTANT GRAPHIC REPRESENTATION
The first cursor proves that at
1us the current is 6.32V
The second cursor is showing that after 5 time constants the inductor represents a short circuit.

19. THEORY
When 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 seconds
Current is 0 Amps
Voltage is Maximum Volts

20. THEORY
As 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. THEORY
Eventually 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 seconds
Current is Maximum Amps
Voltage is 0 Volts

22. Series and Parallel Inductors
Inductors in Series
With several Inductors in series, they all act together to affect the current

23. Series and Parallel Inductors
Inductors in Parallel
With several Inductors in parallel, we have to split the current, just like in resistors

24. End of Presentation