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1 전기공학은전력을발생시키고이를수송하며각사용자가이를유용하게쓸수있도록하는학문분야이다. 전기공학 그림에서보는바와같이발전소의발전기 ( 대개는동기기 ( 同期機 )) 가발전을하여이것을삼상 ( 三相 ) 으로송전한다. 이것은변전소와배전소를거쳐단상 ( 單相 ) 으로가정에공급된다. 가정에서는전자파 ( 電磁波 ) 로수송되는 TV신호를받아 TV를볼수있다. TV에는트랜지스터, Op Amp(Operational Amplifier), 인덕터, 캐패시터등의회로소자를사용하고있다. Lecture 1-1 전기시스템 (I) A : TV signal : 주파수 MHz 8 파장. m/s λ = c 3 10 = f f 1/s Ch2 : 60 MHz 파장 =5m Ch54 : 1,500 MHz 파장 =0.2m B : 전자파의형태로전파. C : 전자파가안테나에서전하와전류를유도. G : 집으로들어오는전압은변압기에의해강압 ( 降壓 ) 됨. F : TV 를보는사람의심장에도전류가흐르고있음. D : 전자가전계에의해가속이되어 CRT 면을때려서빛을발함 E : 트랜지스터내의전자와정공 ( 正孔 ) 의움직임으로신호를처리 Lecture 1-2 1

2 전기시스템 (II) Lecture 1-3 Frequency (Hz) 전기시스템 (III) Individual bands of the radio spectrum and their primary applications Lecture 1-4 2

전기시스템 (IV) K : 만들어진전력은삼상 ( 三相 ) 회선에의해서수송되며,

송전선의전압과전류가만들어내는전계와자계의영향을받을수있음 I : 화력발전소에서발생하는미진 (

H : 동기발전기에의해서전력이만들어짐. J : 조정실의컴퓨터에의해전력이분배되고제어되어짐.

2-4 Base Scientific notation on a calculator EE

3 전기시스템 (IV) K : 만들어진전력은삼상 ( 三相 ) 회선에의해서수송되며, 이선들은절연체에의해송전탑으로부터절연되고있음 L : 송전선아래에사람이서있는경우, 송전선의전압과전류가만들어내는전계와자계의영향을받을수있음 I : 화력발전소에서발생하는미진 ( 微塵 ) 을정전력으로포집 ( 捕集 ) 하는집진기 ( 集塵機 ). H : 동기발전기에의해서전력이만들어짐. J : 조정실의컴퓨터에의해전력이분배되고제어되어짐. Lecture 1-5 Scientific Notation Scientific notation 150,000 -> 1.5 x > 22x Base Scientific notation on a calculator EE key in calculator 10 x Exponent Example Enter 23,560 in scientific notation using EE key. solution) EE E4 Lecture 1-6 3

Engineering Notation Engineering notation The power-of-ten exponent must be a multiple of three. 33,000 -> 33 x 10 3 0.

4 Engineering Notation Engineering notation The power-of-ten exponent must be a multiple of three. 33,000 -> 33 x > 45 x 10-3 Engineering notation on a calculator Automatically convert any decimal number entered into scientific notation or engineering notation. Example Enter 51,200,000 in engineering notation using EE key solution) EE E6 Lecture 1-7 Systems of Units 1960 년 General Conference of Weights and Measures 에서 SI units 를정했다. SI units (Syste me International (in French)) Lecture 1-8 4

Derived Units in SI 기본단위들을조합하면유도단위를나타낼수있다. 예 : C = A s, W=J/s Lecture 1-9 Units, SI Prefixes and Variables Notation 사람의이름을딴단위는대문자로쓴다. 기호다음에마침표 (period) 를찍지않고, 기호에복수형은쓰지않는다.

5 Derived Units in SI 기본단위들을조합하면유도단위를나타낼수있다. 예 : C = A s, W=J/s Lecture 1-9 Units, SI Prefixes and Variables Notation 사람의이름을딴단위는대문자로쓴다. 기호다음에마침표 (period) 를찍지않고, 기호에복수형은쓰지않는다. 단위는정자체 ( 正字體 ) 로쓰고, 숫자와단위사이는띄어쓰기를한다. 예 : 100 m (o), 100 m (x), 100m (x). 변수표현법 변수는기울임체로쓴다. 윗첨자와아래첨자의경우, 숫자는정자체로, 알파베트는기울임체로쓴다. 예 : v x, v 1, 100 V( 여기서 V는단위임 ) 을의미하는 k 는소문자. 1/100 을의미하는 c 는소문자. Lecture

6 Error, Accuracy and Precision Data taken in experiments are not perfect. Experimental error should not be thought of a mistake. The difference between the true or best-accepted value of some quantity and the measured value is the error. Accuracy is an indication of the range of error in a measurement. Precision is a measure of repeatability (or consistency) of a measurement of some quantity. It is possible to have a precise measurement in which a series of readings are not scattered, but each measurement tis inaccurate because of an instrument t error. For example, a meter may be out of calibration and produce inaccurate but consistent (precise) results. However, it is not possible to have an accurate instrument unless it is also precise. } Error Precise, but not accurate. Lecture Significant Digits The digits in a measured number that are known to be correct are called significant digits. 유효숫자들의적절한수사용은실험값의기록에있어서정확도를높이는방법이다. 측정의보다높은정밀도는방법에있어서유효숫자의수를많게하는것. 예를들면, 길이측정에있어서 mm 는유효숫자가 4개임. 반면에 25.5나 25.6은단지3개의유효숫자를가지게된다. 세가지의각각의값들에있어서, 마지막자리수는실험에서의근사치를반영한다. 일반적으로, 확실한값으로알려져있는자리수와첫번째근사자리는유효숫자들로알려져있다. 유효숫자의수는소수점자리의위치와관계되지않는다. 더욱이단지소수점자리를말하는데사용되는 0 들은유효숫자가아니다. 예를들면, 1706, 170.6, 그리고 모두유효숫자가 4개임. 1,540을표현할때, 0 이유효숫자인지아닌지분명하지않다. 유효숫자표기법은이를분명하게하는데사용된다. 유효숫자가 4개인경우, 과같이표현한다. 유효숫자가 3개인경우, 과같이표기한다. Lecture

Calculation of Measured Numbers 덧셈, 뺄셈, 곱셈, 나눗셈으로측정된값은포함하고있는자리수를주의해야한다. 수학적인계산에의해서유효숫자들의수가증가하지는않지만감소할수는있다. 덧셈또는뺄셈 결과에서소수점자리수는소수점위치의수중에가장작은수가결정한다. a) 145.23 + 22.6 = 167.83 => 167.8 b) 145.23-22.

2 = 3.924 => 3.9 b) 4764/3.82 = 121.623 => 122 변수를이용한곱셈또는나눗셈 변수는유효숫자의무한한수또는무한한정밀도를가지고있는것으로다루어야한다. a) 2 ΔD = 2 x 3.33 = 6.66 b) 1/2 (12.8) = 6.

7 Calculation of Measured Numbers 덧셈, 뺄셈, 곱셈, 나눗셈으로측정된값은포함하고있는자리수를주의해야한다. 수학적인계산에의해서유효숫자들의수가증가하지는않지만감소할수는있다. 덧셈또는뺄셈 결과에서소수점자리수는소수점위치의수중에가장작은수가결정한다. a) = => b) = => c) x x 10 2 = x 10 2 => 7.62 x 10 2 d) x x 10 2 = ( ) x 10 3 => 3.84 x 10 3 곱셈또는나눗셈 결과에서유효숫자의숫자의수는최소유효숫자를가지고있는수이다. a) 3.27 x 1.2 = => 3.9 b) 4764/3.82 = => 122 변수를이용한곱셈또는나눗셈 변수는유효숫자의무한한수또는무한한정밀도를가지고있는것으로다루어야한다. a) 2 ΔD = 2 x 3.33 = 6.66 b) 1/2 (12.8) = 6.4 Lecture Electrical Shock Current through your body, not the voltage, is the cause of electrical shock. Resistance of the human body is typically between 10 kω and 50 kω and depends on the two points between which is measured. For example, if you have a resistance of 10 kω between two given points on your body, 90 V across those two points will produce enough current (9 ma) to cause painful shock. Touch or step potential Touch/step potential Physical effects of electrical current. Values vary depending on body mass. 전류 (ma) 물리적인영향 0.4 약간느낌 1.1 인지의역치 1.8 아픔을느끼지않는쇼크. 근육조절에영향이없음 9 고통스러운쇼크, 근육조절에영향이없음 16 고통스러운쇼크, 역치를넘어섬 23 심한고통의쇼크, 근육수축, 호흡곤란 75 심실세동 ( 細動 ) 의역치 235 5초이상동안치명적인심실세동에영향을줌 4,000 심장마비 ( 심실의세동이멈춤 ) 5,000 생체조직화상 Lecture

8 Safety Precautions (I) 1. 전원과의접촉을피할것. 회로작업을하기전에전력을차단할것. 2. 혼자작업하지말것. 3. 피곤할때나졸음이오는약을복용한후작업하지말것. 4. 시계, 금속반지, 금속팔찌등을착용하지말것. 5. 기기의작업순서나위험성을인지하기전에는작업하지말것. 6. 삼선전력선을사용할것.( 즉, 접지선을사용할것 ) 7. 전력선이양호한상태인지확인하고접지핀을휘게하거나없애지말것. 8. 사용하는도구의절연을확인할것. 9. 도구를적절히사용하고작업장을깨끗이할것. 10. 납땜을하거나와이어를절단할때보호용안경을착용할것. 11. 회로에있는부품을만질때, 반드시전원을차단하고캐패시터를방전시킬것. 12. 비상전원차단기와비상구의위치를파악할것. 13. 중간잠금스위치와같은안전소자를무시하거나함부로고치지말것. 14. 항상마른신발을신고있고, 금속이나젖은바닥위에서서작업하지말것. 15. 젖은손으로계기를동작시키지말것. Lecture Safety Precautions (II) 16. 회로가꺼져있다고믿지말것. 작업하기전에신뢰성있는계기로다시한번점검할것. 17. 회로시험중에필요한전류보다많은전류가공급되는것을막기위하여전기전자전원에전류제한기 ( 예를들면, fuse 등 ) 를사용할것. 18. 캐패시터와같은소자는전원을차단한후긴시간이지나도막대한에너지를저장할수있다. 작업하기전에반드시방전시킬것. 19. 회로를구성할때전압이높다고생각되는곳을가장나중에연결할것. 20. 전원단자와접촉하지않도록할것. 21. 절연된전선을사용하고절연덮개가있는커넥터나클립을사용할것. 22. 전선이나도체를가능한한짧게할것. 분극성소자 ( 캐패시터 ) 를적절히연결할것. 23. 모든불안전한상황을보고할것. 24. 작업장이나실험실의행동규칙을숙지하고따를것. 기기근처에음료와음식을두지말것. 25. 감전된사람을도체로부터떨어뜨릴수없다면, 전원을즉시차단할것. 만약전원을차단할수없으면, 절연체를이용하여그사람을도체로부터떨어뜨릴것. Lecture

전하 전하의중요특성 (1) positive, negative 극성을갖고있다. (2) 전자전하의정수배 (-1 1.6 10-19 C) (3) 전기적효과를발생시킨다. - 전하가분리되면전압이발생, 전하가흐르면전류발생. - 전하양은전자전하양의정수배로불연속하지만워낙작은양 (-1.

9 전하 전하의중요특성 (1) positive, negative 극성을갖고있다. (2) 전자전하의정수배 ( C) (3) 전기적효과를발생시킨다. - 전하가분리되면전압이발생, 전하가흐르면전류발생. - 전하양은전자전하양의정수배로불연속하지만워낙작은양 ( C) 이굉장히많으므로 ( 예 :20ºC구리의경우전자밀도 개 /cm 3 ) 연속적이라고본다. Lecture 전류정의 : 단위시간당전하의알짜흐름. 단위 : C/s = A (amperes) dq i = dt 전류 1 A 는 1 초에 1coulomb 의전하가흐른다는의미. Basic electric circuit Boylestad 책 34 쪽그림 2.7 Lecture

10 전압 전압정의 : 전하를분리시키는데드는단위전하당에너지. 단위 : J/C = V (volts) v = dw dq 1 V 는 1 Joule 의에너지로 1 coulomb 의전하를분리시켰다는의미. Defining the unit of measurement for voltage Boylestad 책 37 쪽그림 2.10 Lecture 에너지와 Power dw dw dq p ( t) = =. = vi dt dq dt + v i v i 1 2 Power : positive 상자안의회로에에너지가전달됨. Power : negative p=vi p=v(-i)=-vi 상자안의회로로부터에너지가나옴. Passive reference configuration Lecture

11 충방전과에너지의흐름 축전지도캐패시터이다. 캐패시터는에너지를저장하기도하고방출하기도한다. 캐패시터에에너지가충전될때에는전류가흘러들어와서전하가축적되며, 전압이상승한다. 방전시에는전류가캐패시터로부터흘러나가축적된전하가줄어들며전압이떨어지게된다. 자동차의축전지를충전하는것도같은원리이다. 충방전시의에너지흐름에대해서생각해보자. A A + v - + v - 전류충전전류방전 + v - + v B B Lecture 1-21 Ideally, a voltage source can provide a constant voltage for any current required by a circuit. Ideal Voltage Source v s + The IV curve for an ideal voltage source has a constant voltage for all current. In practice, ideal sources do not exist, but they can be closely approximated by actual sources. I Voltage is constant t for all currents. Dc voltage sources (1) Batteries (chemical action) (2) Solar cells (photovoltaic effect) (3) Generators (electromechanical) (4) Power supplies (rectification) (5) Thermocouples (Seebeck effect) (6) Piezoelectric sensors (piezoelectric effect) IV characteristics of an ideal voltage source Floyd 책 31 쪽그림 2.9 V Lecture

12 Four basic components Batteries - positive electrode: a deficiency of electrons due to chemical reaction - negative electrode: a surplus of electron due to chemical reaction - electrolyte: the electrolyte provides a mechanism for charge flow between positive and negative electrodes - separator: the separator electrically isolates the positive and negative electrodes. The materials used in a battery cell e- + e- determine the voltage it produces. Lead-acid cell (2.05 V): a potential Zinc Copper (anode) (cathode) of V at the positive electrode, Zn 2+ Zn + 2e- Cu e- a potential of V at the negative electrode. A commercial lead-acid acid cell: 2.15 V (acid concentration) Nickel-cadmium cadmium cells: 1.2 V. ZnSO 4 solution Porous barrier CuSO 4 solution Lithium cells: 4 V. Diagram of a battery cell. Floyd 책 31쪽그림2.10 Cu Lecture 1-23 Types of Batteries Alkaline-MnO 2 Primary battery, palm-type computers, photographic equipment, toys, radios and recorders. Lithium-MnO 2 Primary battery, photographic and electronic equipment, smoke alarms, personal organizers, memory backup and communication equipment. Zinc air Primary battery, hearing aids, medical monitoring instruments, pagers and other frequency-use applications. Silver oxide Primary battery, watches, photographic equipment, hearing aids, and electronics eect csrequiring high-capacity batteries. es Nickel-metal hydride Secondary battery, portable computers, cell phones, camcorders, and other portable consumer electronics. Lead-acid acid Secondary battery, automotive, marine, and other similar applications. Lecture

13 Alkaline Primary Cells (a) Cutaway of cylindrical Energizer alkaline cell; (b) Eveready Energizer primary cells. Boylestad 책 40 쪽그림 2.12 Lecture 1-25 Lithium-Iodine Primary Cells Lithium-Iodine primary cells, Boylestad 책 40 쪽그림 2.13 Lecture

Lead-Acid Secondary Cell - electrolyte : sulfuric acid - electrodes :

- electrons: spongy lead -> lead peroxide during discharge.

6-V) lead-acid battery Boylestad 책 41 쪽그림 2.

batteries. Boylestad 책 42 쪽그림 2.15 1000 charge/discharge cycles.

14 Lead-Acid Secondary Cell - electrolyte : sulfuric acid - electrodes : spongy lead and lead peroxide. - electrons: spongy lead -> lead peroxide during discharge. Maintenance-free 12-V (actually 12.6-V) lead-acid battery Boylestad 책 41 쪽그림 2.14 방전량은 specific gravity를측정하면알수있다 ~ 1.30 이면정상이고, 1.1 정도이면충전해야한다. 충전하기위해서는 dc current source 가필요하다. Lecture 1-27 Nickel-Cadmium Secondary Cell Rechargeable nickel-cadmium batteries. Boylestad 책 42 쪽그림 charge/discharge cycles. Ni-Cad battery를사용해야하는기구에일차건전지를사용하면안된다. 이차전지는 1.2 V 이나, 일차전지는 1.5 V 이며, 이차전지를사용하는기구는내부에충전하는회로를갖고있기도하기떄문이다. Ni-Cad battery 는충전할때거의단자전압이변하지않으면서정전류원으로충전한다. 그러나, lead-acid battery 는 battery의상태에따라전류량이변하는정전압원에의해서충전된다. Lecture

Ampere-Hour Rating Battery 의용량정격은 Ah 또는 mah 로표시. 전류량이많아지면줄고, 상온보다높거나낮으면준다. 단자전압은방전시간이길어지면줄어든다.

capacity versus discharge current; (b) capacity versus temperature. Boylestad 책 44 쪽그림 2.

19 Lecture 1-29 Solar Cells Photovoltaic effect A basic solar cell consists of two layers of different types

electron acquire enough energy to break away from their parent atoms and cross the junction.

15 Ampere-Hour Rating Battery 의용량정격은 Ah 또는 mah 로표시. 전류량이많아지면줄고, 상온보다높거나낮으면준다. 단자전압은방전시간이길어지면줄어든다. ampere hour rating(ah) Life(hours) = amperes drawn(a) 24 0 C Eveready BH 500 cell characteristics: (a) capacity versus discharge current; (b) capacity versus temperature. Boylestad 책 44 쪽그림 2.18 Eveready BH 500 cell discharge curves. Boylestad 책 44 쪽그림 2.19 Lecture 1-29 Solar Cells Photovoltaic effect A basic solar cell consists of two layers of different types of semiconductive materials joined together to form a junction When one layer is exposed to light, many electron acquire enough energy to break away from their parent atoms and cross the junction. This process forms negative ions on one side of the junction and positive ions on the other and thus a potential difference (voltage ) is developed. Construction of a basic solar cell Floyd 책 33 쪽그림 2.13 Lecture

16 Dc Voltage Generators Dc generators : 120 V or 240 V Cutaway view of a dc voltage generator Floyd 책 33 쪽그림 2.14 dc generator Boylestad 책 45 쪽그림 2.20 Lecture 1-31 Electronic Power Supplies Power Supplies : Rectification and filtering (a) available terminals; (b) positive voltage with respect to (w.r.t) ground; (c) negative voltage w.r.t. ground; (d) floating supply Boylestad 책 46 쪽그림 2.22 dc laboratory supply. Boylestad 책 45 쪽그림 2.21 Lecture

17 Thermocouples and Piezoelectric Sensors Thermocouples - Thermoelectric type of voltage source that is commonly used to sense temperature. - A thermocouple is formed by the junction of two dissimilar metals. - Seebeck effect : the voltage generated at the junction of the metals as a function of temperature. - K type : chromel and alumel - E, J, N, B, R and S. - Wire and probe form. Piezoelectric Sensors - Piezoelectric effect: A voltage is generated when a piezoelectric material is mechanically deformed by an external force. - Quartz and ceramic - Pressure sensors, force sensors, accelerometers, microphones, ultrasonic devices. Lecture 1-33 Ideal Current Source Ideally, a current source can provide a constant voltage in any load. The IV curve for an ideal current source has a constant current for all voltage. In practice, ideal current sources do not exist, but they can be closely approximated by actual sources. I Current is constant for all voltages. I s V IV characteristics of an ideal current source Floyd 책 36 쪽그림 2.19 Lecture

18 Current Sources: Transistors Circuits In most transistor circuits, the transistor acts as a current source. The flat part of graph indicates where the transistor current is constant over a range of voltages. The constant-current current region is used to form a constant-current current source. I (current through the transistor) V (voltage across the transistor) Characteristic curve of a transistor showing the constant-current region Floyd 책 37 쪽그림 2.21 Lecture 1-35 Constant-Current Current Battery Chargers The rectifier is a circuit that acts as a dc voltage source by converting the ac voltage from a standard wall outlet to a dc voltage. This voltage is effectively applied in parallel with a battery and in series with a constant-current current source. The battery voltage is initially low but increases over time due to the constant charging current. V constant current source = V constant dc voltage source -V battery Constant current source AC voltage Voltage rectifier + + Constant dc Battery voltage increases voltage - - as it charges. Battery charger as an example of a current source application Floyd 책 37 쪽그림 2.22 Lecture

Applications - Flashlight (a) Eveready D cell

flashlight of part (a); (c) Duracell Powercheck

Bulb 보다 battery 를자주교체하는이유 (1) leakage current

initial surge current Battery 는대개1.2 ~ 1.

Lecture 1-37 Applications 12 V Car Battery

19 Applications - Flashlight (a) Eveready D cell flashlight; (b) electrical schematic of flashlight of part (a); (c) Duracell Powercheck D cell battery Boylestad 책 51 쪽그림 2.29 Battery : 16 Ah Bulb : 2.5 V, 300 ma, 30 hours. Bulb 보다 battery 를자주교체하는이유 (1) leakage current (2) 연속사용이아님 - bulb: cool down 효과 - battery: initial surge current Battery 는대개1.2 ~ 1.3 V 에서동작. 0.9 V 이하에서는교체해야함. Lecture 1-37 Applications 12 V Car Battery Charger Battery charger: (a) external appearance Boylestad 책 53 쪽그림 2.30(a) Battery charger: (b) internal construction Boylestad 책 53 쪽그림 2.30(b) Lecture

Applications 12 V Car Battery Charger Circuit 12 V 이상일때충전. 12 V 이하에서는 diode 때문에방전이안됨.

또한, battery 전압이낮을때흐르는대전류를차단시켜야한다. Electrical schematic for the battery charger of Fig.2.

Answer Machines/Phones dc Supply Answering machine/phone 9-V dc supply Boylestad 책 55 쪽그림 2.

20 Applications 12 V Car Battery Charger Circuit 12 V 이상일때충전. 12 V 이하에서는 diode 때문에방전이안됨. 6 A 충전모드사용시, 처음에는 7~8 A 가흐르나충전이진행함에따라 2~3 A 로떨어진다. 충분히충전이되면충전을정지시켜야한다. 또한, battery 전압이낮을때흐르는대전류를차단시켜야한다. Electrical schematic for the battery charger of Fig Boylestad 책 54쪽그림2.31 Lecture 1-39 App. Answer Machines/Phones dc Supply Answering machine/phone 9-V dc supply Boylestad 책 55 쪽그림 V, 200 ma. Regulator chip 을수신단에설치. 이유 - 발생열분리 - 잡음과진동을줄이기위해부하가까이에설치. Internal construction of the 9-V dc supply of Fig Boylestad 책 55 쪽그림 2.33 Lecture

21 Jet Valve Controller 작은실험용우주로켓에서그림과같이두개의회로소자로회로를구성하여 1분간 jet valve 제어기에에너지를전달한다. 1분간 40 mj을전달하는배터리 ( 회로소자 1) 를골라야한다. i(t) =De t/60 ma for t >= 0 이고, 소자 2 에걸리는전압은 v 2 (t) =Be t/60 V for t >= 0 이다. 전류의크기 D 가최대1mA로제한되어있다면, B 는얼마이어야하나? 요구되는배터리는어떤것인가? Jet valve controller Lecture

Microsoft PowerPoint - lec01_2005

Microsoft PowerPoint - lec01_2005 전기공학은전력을발생시키고이를수송하며각사용자가이를유용하게쓸수있도록하는학문분야이다. 전기공학 그림에서보는바와같이발전소의발전기 ( 대개는동기기 ( 同期機 )) 가발전을하여이것을삼상 ( 三相 ) 으로송전한다. 이것은변전소와배전소를거쳐단상 ( 單相 ) 으로가정에공급된다. 가정에서는전자파 ( 電磁波 ) 로수송되는 TV신호를받아 TV를볼수있다. TV에는트랜지스터, Op