Download Inductors: Properties, I-V Characteristics, and Energy Storage and more Slides Fundamentals of Electronics in PDF only on Docsity! Lecture Twenty Inductors An inductor is a circuit element that consists of a conducting wire usually in the form of coil. Inductors are typically categorized by the type of core on which they are wound. The core material may be air, or any non‐magnetic material, iron or ferrite. As we know that a magnetic field (or magnetic flux), Φ, is present around every wire that carries an electric current. If a conductor is wound in a single turn, the resulting magnetic flux will flow in the common direction through the centre of the coil. A coil with N turns would produce a magnetic filed that is present in the form of continuous path through and around the coil. The ability of coil to oppose any change in current is a measure of the self inductance (or merely inductance) L of the coil. 2N AL l μ= where μ is the permeability of the core, A is the face area of the core and l is the mean length of the core. The value of μ =B/H is not constant and it depends on value of B = Φ/A (flux density) and H = NI/l. The permeability of free space is μ0 = 4πx10‐7 Weber/A/m where Weber is the SI unit for magnetic flux. Practically speaking, the permeability of all non‐magnetic materials such as copper, aluminum, wood, glass or air is same as that for free space. Materials with permeability slightly less than μ0 are called diamagnetic, and those with permeabilities slightly greater than μ0 are called paramagnetic. Ferro‐magnetic materials (iron, cobalt, nickel, steel and there alloys) have high permeability (100s or even 1000s times μ0). The ratio of permeability of a material to that of free space is called relative permeability 0 r μμ μ = docsity.com For ferromagnetic materials, μr ≥100 and for non‐magnetic materials μr = 1. Putting μ = μrμ0, the inductance can be rewritten as 2 0 r N AL l μμ= I‐V Characteristics Putting μ = B/H where B = Φ/A and H = NI/l, the inductance becomes L N I Φ = But inductance is the measure of change of flux due to change in current therefore dL N di ϕ = According to Faraday’s law, if a coil of N turns is placed in the region of changing flux, a voltage will be induced across the coil d d di div N N L dt di dt dt ϕ ϕ = = = or ( )( ) di tv t L dt = The power delivered to the inductor is ( )( ) ( )di tp t L i t dt = And energy stored in magnetic filed is 21( ) ( ) ( ) ( ) ( ) ( ) Joules 2L E t L p t d t L i t di t Li t= = =∫ ∫ Example: Determine the voltage waveform if the current in 10 mH has a waveform 0 20m 0 2ms 0 2m 20m 0( ) 40m 2ms 4ms 2m 4m 0 4ms t t i t t t t −⎧ ≤ ≤⎪ −⎪ −⎪= + ≤ ≤⎨ −⎪ ≥⎪ ⎪⎩ docsity.com Example: Prove that inductors combines like resistances If the number of inductors are connected in series then according to KVL 1 2 1 2 1 ( ) ( ) ( ) ( )N N N i S i v t v t v t v t di di diL L L dt dt dt diL L dt= = + + + = + + + ⎧ ⎫ = =⎨ ⎬ ⎩ ⎭ ∑ where 1 2 1 N S i N i L L L L L = = = + + +∑ For inductors combined in parallel, the KCL applies 0 0 0 0 0 1 2 1 0 2 0 0 1 2 0 1 1 0 ( ) ( ) ( ) ( ) 1 1 1( ) ( ) ( ) ( ) ( ) ( ) 1( ) ( ) 1( ) ( ) N t t t N Nt t t tN N i i i i t t P t i t i t i t i t i t v x dx i t v x dx i t v x dx L L L i t v x dx L i t v x dx L = = = + + + ⎧ ⎫ ⎧ ⎫ ⎧ ⎫⎪ ⎪ ⎪ ⎪ ⎪ ⎪= + + + + + +⎨ ⎬ ⎨ ⎬ ⎨ ⎬ ⎪ ⎪ ⎪ ⎪ ⎪ ⎪⎩ ⎭ ⎩ ⎭ ⎩ ⎭ = + = + ∫ ∫ ∫ ∑ ∑ ∫ ∫ where 1 1 2 1 1 1 1 1N iP i NL L L L L= = = + + +∑ docsity.com Example: Compute the equivalent inductance if all inductors are 6mH 1 2 3 4 5 6 1 2 3 4 5 2 3 1 3 1 2 6 1 2 3 4 5 2 3 1 3 1 2 1 2 3 5 4 5 2 3 1 3 1 2 6 1 2 3 4 5 2 3 1 3 1 2 4 2 2 2 2 ( ) ( ) ( )( ) .3 11 4.43mH 2 .3 7 eqL L L L L L L L L L L L L L L L L L LL L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L L = + + ⎛ ⎞ +⎜ ⎟+ +⎝ ⎠= + + + + + + + + = + + + + + + = + = = + docsity.com