ELECTRONICS E # 1 FUNDAMENTALS 2/2/2011

Transcription

1 FE Review 1 ELECTRONICS E # 1 FUNDAMENTALS

2 Electric Charge 2 In an electric circuit it there is a conservation of charge. The net electric charge is constant. There are positive and negative charges. Like charges repel while unlike charges attract. The SI unit for electric charge (q) is the Coulomb (C)

3 Electric Energy 3 Energy is the ability to perform work and has the same units as work: Work = force x dist. The SI unit for energy (w) is the Joule (J).

4 Basic Variables 4 Quantity Symbol Unit Mass m,m kg Length ll l,l meter,m m Time t sec, s Energy w,w joule, J charge q,q coulomb, C Lower case usually indicates a time variant unit.

5 Electric Current 5 Charge is moved through a circuit as current, which is simply a measure of the charge transferred/sec. The SI unit is the Ampere with ih the symbol bl (A). i dq Q Coulombs I dt t s

6 Voltage 6 The work performed/unit charge while moving a charge from one point to another in a circuit is voltage. Voltage is analogous to pressure. The SI unit for voltage is the volt (v) dw joules V volts dq coulomb I V

7 Power 7 Power P, dw dt joules sec P VI watt, w P or watt Power is defined as the rate of energy transfer

8 Resistance 8 Resistance (R) unit is the Ohm ( ) A resistance is an element which dissapates energy and can not store energy V i Ohm 's Law V IR R V R I I R V

9 Capacitance 9 A capacitor is an element which stores energy in an electric field. This energy is returned to the circuit later. The SI unit for capacitance (C) C i dv dt is the farad, F. I C Alternate Symbol V 1 t i C dv an d V i(t)dt V(0) dt C o

10 Inductance 10 An inductor (Coil) is an element which stores energy in a magnetic field. The energy is the returned to the circuit later. The SI unit for v L= or v=l di dt Inductance (L) is the Henry, H. di dt 1 i t dt i 0 L 0 t nd i= v t dt i 0 an I L V

11 Electrical variables 11 Quantity Symbol Unit Current i(i) Ampere, A Voltage v(v) Volt, V Power p(p) Watt, W Resistance R Ohm, Capacitance C Farad, F Inductance n L Henry, H

12 Some definitions 12 R C C 2 1 L nodes 4 loops 3 meshs E 2 also known as panes

13 Kirchhoff s Voltage Law (KVL) 13 KVL : V 0 closed loop V 1 V 5 V 4 V 3 V 2 V1 V2 V3 V4 V5 0

14 Kirchhoff s Current Law(KCL) KCL i 0 node 14 currents entering a node are defined as currents leaving a node are define d as i i i i

15 Total Resistance of Series Elements 15 When resistors are in series, the total resistance is simply the sum of the resistors. R T 5v 10k 2k 5k RT 10 k 5 k 2 k 17 k

16 KVL/KCL Example 1 16 Determine the unknown voltages, currents, and R in the circuit to the right. 21v I 1 6k V 1 3k I 2 I 3 KVL loop Step 1: Perform a KVL to find the voltage across the 2 parallel resistors, V 1 : V 1 The 2 resistors share the same voltage. 9v 0 21v 9v V 1 21v I 4 R 9v 12v Example continued on the next slide.

17 KVL/KCL Example 1 (cont) 17 Now that V 1 is known, the currents thru the 2 parallel resistors can be found via Ohm s Law. I2 12v 12v 2mA I3 4mA 6k 3k Example continued on the next slide.

18 KVL/KCL Example 1 (cont) 18 Next, use KCL to determine the value of I 1. Perform a KCL at the node to the left of the parallel combination: 0 I 2mA 4mA I1 1 6mA Finally, with the value of I 1, use Ohm s law to determine the value of R: VR 9v R 1.5 k I 6mA 1

19 V V 1 2 V Voltage Divider example 30 5k 5k10k15k 150 5v k 30k v v V 1 R 1 (5k) R 2 (10k) R 3 (15k) V 2 V 3 V k15k 30 15k 30k 30k v v 3 V 4

20 Current Divider example 20 I R 1 T 10A 6k 3k 2k 10A 2k 6k 2k 2k 20A 5A 4 3k 1 1k k 3k 2k I T 10A I 3 I 1 I 2 R 3 (6k) 2 R 2 (3k) R 1 (2k) 2k 3k R1 R2 R 1.2k 1 2 R1 R2 2k 3k

21 Example 21 Find all voltages and currents. Verify with KVL. 8v 1 st, reduce the circuit. Req1 R R R eq R R 2 e q v i 1 R 1 24 V 1 R 1 i 1 R 1 i 3 i 2 R 3 V 2 24 V 1 V 2 R 2 18 V 4 R 4 5 R eq V 3 16 Example continued on the next slide.

22 Example (continued) 22 I 1 8v mA V I R V i 1 R 1 24 V 1 V 2 R eq2 8v I R 2 1 eq mA mA v v Example continued on the next slide.

23 Example (continued) 23 i 1 R 1 24 i 3 8v V 1 i 2 R V R eq1 21 V 4 R V 3 R 3 16 I 2 V 2 R v m A Example continued on the next slide.

24 Example (continued) i 1 R i 3 8v V 1 i 2 V 2 R 2 18 V 4 V 3 R 3 16 I 3 R eq1 21 R 4 5 IR 1 2 R2 Re q1 0 I1 I2 I mA 18 I3 I1 I2 or mA mA mA mA Difference is due to round of f.

25 Sources 25 Ideal AC voltage source Ideal DC voltage source Nonideal DC voltage source e(t) E E R s i(t) () I I R R s Ideal AC current source Ideal DC current source Nonideal DC current source

26 Waveform shape 1. i t I 4 dc current 2. v(t) 2e 3t 26 25cos 3. v t t AC voltage aperiodic associated with transients AC voltage periodic associated with steady state analysis

27 The Sine Wave v A T 27 sin t cos t 2 cos t sin t 2 t 1 cycles f hz 2 T sec 2 ft Asin t T phase if shifts left phase if shifts right

28 Average Value 28 1 T V avg T 0 v t dt

29 Effective value 29 T 1 2 P eff P t dt T Essentially, effective heating value How much power will it use. 0

30 Instantaneous Power 30 P VI