Elektronika (11)

Elektronika AgusSetyo Budi, Dr. M.Sc Sesion #11 JurusanFisika FakultasMatematikadanIlmuPengetahuanAlam

Outline 19-1: Induction by Alternating Current 19-2: Self-InductanceL 19-3: Self-Induced Voltage vL 19-4: How vL Opposes a Change in Current 19-5: Mutual Inductance LM 19-6: Transformers 19-7: Transformer Ratings 19-8: Impedance Transformation 19-9: Core Losses 19-10: Types of Cores 19-11: Variable Inductance 19-12: Inductances in Series or Parallel 19-13: Energy in Magnetic Field of Inductance 19-14: Stray Capacitive and Inductive Effects 19-15: Measuring and Testing Inductors © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 2 07/01/2011

19-1: Induction by Alternating Current Induced voltage is the result of flux cutting across a conductor. This action can be produced by physical motion of either the magnetic field or the conductor. Variations in current level (or amplitude) induces voltage in a conductor because the variations of current and its magnetic field are equivalent to the motion of the flux. Thus, the varying current can produce induced voltage without the need for motion of the conductor. This ability is called self-inductance, or simply inductance. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 4

19-1: Induction by Alternating Current Induction by a varying current results from the change in current, not the current value itself. The current must change to provide motion of the flux. The faster the current changes, the higher the induced voltage. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 5

19-1: Induction by Alternating Current ,[object Object]

At point B, the positive direction of current provides some field lines taken here in the counterclockwise direction.Fig. 19-1: Magnetic field of an alternating current is effectively in motion as it expands and contracts with the current variations. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 6

19-1: Induction by Alternating Current ,[object Object],The next half-cycle of current allows the field to expand and collapse again, but the directions are reversed. ,[object Object]

19-1: Induction by Alternating Current Characteristics of inductance are important in: AC circuits: In these circuits, the current is continuously changing and producing induced voltage. DC circuits in which the current changes in value: DC circuits that are turned off and on (changing between zero and its steady value) can produce induced voltage. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 9

19-2: Self-Inductance L The symbol for inductance is L, for linkages of magnetic flux. VL is in volts, di/dt is the current change in amperes per second. The henry (H) is the basic unit of inductance. One henry causes 1 V to be induced when the current is changing at the rate of 1 A per second. VL L = di / dt 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 10

19-2: Self-Inductance L Inductance of Coils The inductance of a coil depends on how it is wound. A greater number of turns (N) increases L because more voltage can be induced (L increases in proportion to N). More area enclosed by each turn increases L. The L increases with the permeability of the core. The L decreases with more length for the same number of turns, as the magnetic field is less concentrated. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 11

19-2: Self-Inductance L Calculating the Inductance of a Long Coil d iron-core symbol air-core symbol (μr = 1) (μr >> 1) N 2A L = 1.26 × 10−6 H μr l Where: ,[object Object]

μris the relative permeability of the core

A is the area in square meters

19-2: Self-Inductance L Typical Coil Inductance Values Air-core coils for RF applications have L values in millihenrys (mH) and microhenrys (μH). Practical inductor values are in these ranges: 1 H to 10 H (for iron-core inductors) 1 mH (millihenry) = 1 × 10-3 H 1 mH (microhenry) = 1 × 10-6 H 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 13

19-3: Self-Induced Voltage vL ( ) ( ) di di ,[object Object],vL L = dt dt ,[object Object]

19-3: Self-Induced Voltage vL Energy Stored in the Field LI 2 = Energy 2 Where the energy is in joules: ,[object Object]

19-4: How vL Opposes a Change in Current Lenz’ Law states that the induced voltage produces current that opposes the changes in the current causing the induction. The polarity of vL depends on the direction of the current variation di. When di increases, vL has polarity that opposes the increase in current. When di decreases, vL has opposite polarity to oppose the decrease in current. In both cases, the change in current is opposed by the induced voltage. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 16

19-5: Mutual Inductance LM Mutual inductance (LM) occurs when current flowing through one conductor creates a magnetic field which induces a voltage in a nearby conductor. Two coils have a mutual inductance of 1 H when a current change of 1A/s induces 1 V in the other coil. Unit: Henrys (H) Formula: = L k L L M 1 2 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 17

19-5: Mutual Inductance LM Coefficient of coupling, k, is the fraction of total flux from one coil linking another coil nearby. Specifically, the coefficient of coupling is k = flux linkages between L1 and L2divided by flux produced by L1 There are no units for k, because it is a ratio of two values of magnetic flux. The value of k is generally stated as a decimal fraction. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 18

19-5: Mutual Inductance LM The coefficient of coupling is increased by placing the coils close together, possibly with one wound on top of the other, by placing them parallel, or by winding the coils on a common core. A high value of k, called tight coupling, allows the current in one coil to induce more voltage in the other. Loose coupling, with a low value of k, has the opposite effect. Two coils may be placed perpendicular to each other and far apart for essentially zero coupling to minimize interaction between the coils. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 19

19-5: Mutual Inductance LM Tighter coupling Loose coupling Zero coupling Unity coupling Fig. 19-8: Examples of coupling between two coils linked by LM. (a) L1 or L2on paper or plastic form with air core; k is 0.1. (b) L1 wound over L2 for tighter coupling; k is 0.3. (c) L1and L2on the same iron core; k is 1. (d) Zero coupling between perpendicular air-core coils. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 20

19-5: Mutual Inductance LM Calculating LM Mutual inductance increases with higher values for primary and secondary inductances. LM where L1 and L2 are the self-inductance values of the two coils, k is the coefficient of coupling, and LM is the mutual inductance. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 21

19-6: Transformers Transformers are an important application of mutual inductance. A transformer has two or more windings with mutual inductance. The primary winding is connected to a source of ac power. The secondary winding is connected to the load. Fig. 19-11: Iron-core power transformer. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 22

19-6: Transformers The transformer transfers power from the primary to the secondary. Transformer steps up voltage (to 100V) and steps current down (to 1A) Fig. 19-9: Iron-core transformer with 1:10 turns ratio. Primary current IP induces secondary voltage VS, which produces current in secondary load RL. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 23

19-6: Transformers A transformer can step up or step down the voltage level from the ac source. Primary Secondary Load Step-up (VLOAD > VSOURCE) Primary Load Secondary Step-down (VLOAD < VSOURCE) A transformer is a device that uses the concept of mutual inductance to step up or step down an alternating voltage. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 24

19-6: Transformers Turns Ratio The ratio of the number of turns in the primary to the number in the secondary is the turns ratio of the transformer. Turns ratio equals NP/NS. where NP equals the number of turns in the primary and NS equals the number of turns in the secondary. The turns ratio NP/NS is sometimes represented by the lowercase letter a. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 25

19-6: Transformers The voltage ratio is the same as the turns ratio: VP / VS = NP / NS VP= primary voltage, VS = secondary voltage NP = number of turns of wire in the primary NS = number of turns of wire in the secondary When transformer efficiency is 100%, the power at the primary equals the power at the secondary. Power ratings refer to the secondary winding in real transformers (efficiency < 100%). 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 26

19-6: Transformers Voltage Ratio 1:3 Primary Secondary Load 120 V 360 V 3:1 Primary Secondary Load 120 V 40 V VL = 3 x 120 = 360 V Step-up (1:3) Step-down (3:1) VL = 1/3 x 120 = 40 V 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 27

19-6: Transformers Current Ratio is the inverse of the voltage ratio. (That is voltage step-up in the secondary means current step-down, and vice versa.) The secondary does not generate power but takes it from the primary. The current step-up or step-down is terms of the secondary current IS, which is determined by the load resistance across the secondary voltage. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 28

19-6: Transformers Current Ratio 1:3 120 V Primary Secondary Load 360 V 0.3 A 0.1 A 3:1 Primary Secondary Load 120 V 40 V 0.3 A 0.1 A IL = 1/3 x 0.3 = 0.1 A IS/IP = VP/VS IL = 3 x 0.1 = 0.3 A 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 29

19-6: Transformers Transformer efficiency is the ratio of power out to power in. Stated as a formula % Efficiency = Pout/Pin x 100 Assuming zero losses in the transformer, power out equals power in and the efficiency is 100%. Actual power transformers have an efficiency of approximately 80 to 90%. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 30

19-6: Transformers Transformer Efficiency 3:1 120 V 40 V Primary Secondary Load 0.3 A 0.12 A PPRI = 120 x .12 = 14.4 W PSEC = 40 x 0.3 = 12 W PSEC 12 × 100 % = 83 % Efficiency = × 100 % = PPRI 14.4 Primary power that is lost is dissipated as heat in the transformer. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 31

19-6: Transformers Loaded Power Transformer ,[object Object]

19-6: Transformers Autotransformers An autotransformer is a transformer made of one continuous coil with a tapped connection between the end terminals. An autotransformer has only three leads and provides no isolation between the primary and secondary. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 33

19-7: Transformer Ratings Transformer voltage, current, and power ratings must not be exceeded; doing so will destroy the transformer. Typical Ratings: Voltage values are specified for primary and secondary windings. Current Power (apparent power – VA) Frequency 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 34

19-7: Transformer Ratings Voltage Ratings Manufacturers always specify the voltage rating of the primary and secondary windings. Under no circumstances should the primary voltage rating be exceeded. In many cases, the rated primary and secondary voltages are printed on the transformer. Regardless of how the secondary voltage is specified, the rated value is always specified under full load conditions with the rated primary voltage applied. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 35

19-7: Transformer Ratings Current Ratings Manufacturers usually specify current ratings only for secondary windings. If the secondary current is not exceeded, there is no possible way the primary current can be exceeded. If the secondary current exceeds its rated value, excessive I2R losses will result in the secondary winding. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 36

19-7: Transformer Ratings Power Ratings The power rating is the amount of power the transformer can deliver to a resistive load. The power rating is specified in volt-amperes (VA). The product VA is called apparent power, since it is the power that is apparently used by the transformer. The unit of apparent power is VA because the watt is reserved for the dissipation of power in a resistance. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 37

19-7: Transformer Ratings Frequency Ratings Typical ratings for a power transformer are 50, 60, and 400 Hz. A power transformer with a frequency rating of 400 Hz cannot be used at 50 or 60 Hz because it will overheat. Many power transformers are designed to operate at either 50 or 60 Hz. Power transformers with a 400-Hz rating are often used in aircraft because these transformers are much smaller and lighter that 50- or 60-Hz transformers. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 38

19-8: Impedance Transformation Transformers are often used to change or transform a secondary load impedance to a new value as seen by the primary. The secondary load impedance is said to be reflected back into the primary and is called a reflected impedance. The reflected impedance of the secondary may be stepped up or down. An equation for the reflected impedance is: 2 æ ö N = ´ P ç ÷ Z Z P S è ø N secondary primary S 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 39

19-8: Impedance Transformation If the turns ratio NP/NS is less than 1, ZS will be stepped down in value. Transformer impedance matchingis related to the turns ratio: N Z = P P N Z S S 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 40

19-8: Impedance Transformation 1:3 ZRATIO = 1/9 Primary Secondary Load = 9 W The load on the source is 1 W. 3:1 ZRATIO = 9/1 Primary Secondary Load = 9 W The load on the source is 81 W. ,[object Object],07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 41

19-8: Impedance Transformation Internal resistance (ri) is 200 Ω. RL is 8 Ω. Fig. 19-20: Transferring power from an amplifier to a load RL. (a) Amplifier has ri = 200 Ω and RL = 8 Ω. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 42

19-8: Impedance Transformation Fig. 19-20: (b) Connecting the amplifier directly to RL. Connected as shown, the load receives 1.85 W of power. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 43

19-8: Impedance Transformation Connection shown increases the power delivered to the load. Fig. 19-20(c): Using a transformer to make the 8-ΩRLappear like 200 Ω in the primary. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 44

19-9: Core Losses Eddy Currents Eddy currents are induced in the iron core of an inductor or transformer. Eddy currents raise the temperature of the core. Wasted power is dissipated as heat. Losses increase with frequency. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 46

19-9: Core Losses Hysteresis losses The hysteresis losses result from the additional power needed to reverse the magnetic field in magnetic materials in the presence of alternating current. The greater the frequency, the more hysteresis loss. Air-core coils Air has practically no losses from eddy currents or hysteresis. The inductance for small coils with an air core is, however, limited to low values (e.g. mH or μH). 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 48

19-10: Types of Cores Losses can be reduced by using a laminated core or a powered-iron core. The type of steel used can reduce hysteresis losses. The most common types of insulation are: Laminated core Powdered iron core Ferrite core 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 49

19-10: Types of Cores Laminated core A shell-type core formed with a group of individual laminations. Each laminated section is insulated by a very thin coating of iron oxide. Powdered iron Consists of individual insulated granules pressed into one solid form called a slug. Ferrite core Synthetic ceramic materials that are ferromagnetic. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 50

19-11: Variable Inductance The inductance of a coil may be varied by one of several methods. For larger coils: More or fewer turns can be used by connection to one of the taps on the coil. A slider contacts the coil to vary the number of turns used. Fig. 19-24: Methods of varying inductance. (a) Tapped coil. (b) Slider contact. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 51

19-11: Variable Inductance Figure 19-24 (c) shows the schematic symbol for a coil with a slug of powdered iron or ferrite. Usually, an arrow at the top means that the adjustment is at the top of the coil. Fig. 19-24: Methods of varying inductance. (c) Adjustable slug. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 52

19-11: Variable Inductance The symbol in Fig. 19-24 (d) is a variometer, which is an arrangement for varying the position of one coil within the other. The total inductance of the series-aiding coils is minimum when they are perpendicular. Fig. 19-24: Methods of varying inductance. (d) Variometer. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 53

19-11: Variable Inductance For any method of varying L, the coil with an arrow in Fig. 19-24 (e) can be used. The variac is an autotransformer with a variable tap to change the turns ratio. The output voltage in the secondary can be varied from 0 to approximately 140 V, with a 120-V, 60Hz input. Fig. 19-24: Methods of varying inductance. (e) Symbol for variable L. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 54

19-12: Inductances in Series or Parallel With no mutual coupling: For series circuits, inductances add just like resistances. For parallel circuits, inductances combine according to a reciprocal formula as with resistances. LT = L1 + L2 + L3 + ... + etc. 1 1 1 1 LEQ = + ... + etc. + + L2 L3 L1 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 55

19-12: Inductances in Series or Parallel Series Coils for LM LMdepends on the amount of mutual coupling and on whether the coils are connected series-aiding or series-opposing. Series-aiding means that the common current produces the same direction of magnetic field for the two coils. The series-opposing connection results in opposite fields. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 56

19-12: Inductances in Series or Parallel The coupling depends on the coil connections and direction of winding. Reversing either one reverses the field. Fig. 19-28: Inductances L1 and L2 in series but with mutual coupling LM. (a) Aiding magnetic fields. (b) Opposing magnetic fields. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 57

19-12: Inductances in Series or Parallel To calculate the total inductance of two coils that are series-connected and have mutual inductance, LT = L1 + L2± 2LM The mutual inductance LM is plus, increasing the total inductance, when the coils are series-aiding, or minus when they are series-opposing to reduce the total inductance. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 58

Elektronika (11)

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

Similaire à Elektronika (11)

Similaire à Elektronika (11) (20)

Plus de jayamartha

Plus de jayamartha (20)

Dernier

Dernier (20)

Elektronika (11)