unj fmipa-fisika

1. Elektronika AgusSetyo Budi, Dr. M.Sc Sesion #13 JurusanFisika FakultasMatematikadanIlmuPengetahuanAlam

2. Outline 21-1: Sine-Wave iL Lags vL by 90° 21-2: XL and R in Series 21-3: Impedance ZTriangle 21-4: XL and R in Parallel 21-5: Q of a Coil 21-6: AF and RF Chokes 21-7: The General Case of Inductive Voltage © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 2 07/01/2011

3. Inductive Circuits 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 3

5. The phasors in Fig. 21-1 (c) show the 90° phase angle between iL and vL.

6. The 90° phase relationship between iL and vL is true in any sine-wave ac circuit, whether L is in series or parallel.Fig. 21-1 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 4

7. 21-1: Sine-Wave iL Lags vL by 90° The phase angle of an inductive circuit is 90° because vL depends on the rate of change of iL. The iL wave does not have its positive peak until 90° after the vL wave. Therefore, iL lags vL by 90°. Although iL lags vL by 90°, both waves have the same frequency. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 5

8. 21-2: XL and R in Series When a coil has series resistance, the current is limited by both XL and R. This current I is the same in XL and R, since they are in series. Each has its own series voltage drop, equal to IR for the resistance and IXl for the reactance. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 6

9. 21-2: XL and R in Series Fig. 21-2: 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 7

11. These phasors show only the 90° angle without addition.

12. The method in Fig. 21-3 (b) is to add the tail of one phasor to the arrowhead of the other, using the angle required to show their relative phase.Fig. 21-3: 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 8

14. The resultant of the phasor addition of R and XL is their total opposition in ohms, called impedance, with the symbol ZT.

15. The Z takes into account the 90° phase relation between R and XL.Fig. 21-4: 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 9

16. 21-3: Impedance Z Triangle I = 2 A 40 Ω 50 Ω VA = 100 R = 30 Ω q 30 Ω XL = 40 Ω 40 XL VL VA 30 R = 53° = Tan-1 Θ= Tan-1 VA leads I by 53° 53° I Phase Angle of a Series RL Circuit 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 10

17. 21-4: XL and R in Parallel IT = 5 A IT IL R = 30 Ω XL = 40 Ω VA = 120 IR VA VA 120 120 = = = = = = A IL 3 A IR 4 R 30 40 XL = = A IR2 + IL2 IT = 5 42 + 32 Currents in a Parallel RL Circuit 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 11

18. 21-4: XL and R in Parallel IT = 5 A R = 30 W XL = 40 Ω VA = 120 q 3 A 5 A 4 A 3 IL Θ = Tan −1− = Tan −1− = −37° 4 IR The total current lags the source voltage by 37°. Phase Angle in a Parallel RLCircuit 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 12

20. This phasor triangle is used to find the resultantIT.Fig. 21-6: 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 13

21. 21-4: XL and R in Parallel IT = 5 A R = 30 W XL = 40 W VA = 120 3 A 5 A 4 A 120 VA = = 24Ω ZEQ= 5 IT Impedance of XL and R in Parallel 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 14

22. 21-4: XL and R in Parallel In a parallel circuit with L and R: The parallel branch currents IR and ILhave individual values that are 90° out of phase. IR and IL are added by phasors to equal IT, which is the main-line current. The negative phase angle −Θ is between the line current IT and the common parallel voltage VA. Less parallel XL allows more IL to make the circuit more inductive, with a larger negative phase angle for IT with respect to VA. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 15

23. 21-5: Q of a Coil The ability of a coil to produce self-induced voltage is indicated by XL, since it includes the factors of frequency and inductance. A coil, however, has internal resistance equal to the resistance of the wire in the coil. This internal resistance ri of the coil reduces the current, which means less ability to produce induced voltage. Combining these two factors of XL and ri , the quality or merit of a coil is, Q = XL/ri. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 16

24. 21-5: Q of a Coil Figure Fig. 21-7 shows a coil’s inductive reactance XL and its internal resistance ri. The quality or merit of a coil as shown in Fig. 21-7 is determined as follows: Q = XL/ri Fig. 21-7: 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 17

26. L has practically all the voltage drop with very little of VT across R.

27. The inductance here is used as a choke to prevent the ac signal from developing any appreciable output across R at the frequency of the source.Fig. 21-9 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 18

28. 21-7: The General Case of Inductive Voltage The voltage across any inductance in any circuit is always equal to L(di/dt). This formula gives the instantaneous values of vL based on the self-induced voltage produced by a change in magnetic flux from a change in current. A sine waveform of current I produces a cosine waveform for the induced voltage vL, equal to L(di/dt). This means vL has the same waveform as I, but vL and I are 90° out of phase for sine-wave variations. The inductive voltage can be calculated as IXL in sine-wave circuits. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 19

29. 07/01/2011 © 2010 Universitas Negeri Jakarta | www.unj.ac.id | 20 TerimaKasih