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electronics fundamentals
circuits, devices, and applications
THOMAS L. FLOYD
DAVID M. BUCHLA
chapter 14
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Mutual Inductance
เมื่อนำขดลวดมำวำงใกล้ ๆ กัน กำรเปลี่ยนแปลงที่ฟลักซ์ของขดลวดหนึ่งจะส่งผลไป
ยังอีกขดหนึ่ง เรี ยกว่ำขดลวดทั้งสองมีควำมสัมพันธ์กนั (LM) ซึ่งอำจจะเป็ นได้ท้ งั
กำรเพิ่มหรื อลดกำรเหนี่ยวนำรวม
LM
ค่ำสัมประสิ ทธิ์ของกำรเหนี่ยวนำ เป็ น
ค่ำที่ใช้วดั ว่ำขดลวดทั้งคู่มีกำรเหนี่ยวนำ
ระหว่ำงกันดีเพียงใด ซึ่งมีค่ำอยูร่ ะหว่ำง
0 และ 1
L2
L1
k
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Mutual Inductance
ค่ำเหนี่ยวนำสัมพันธ์หำได้จำก
LM  k L1L2
k = สัมประสิ ทธิ์กำรเหนี่ยวนำ
L1, L2 = ค่ำกำรเหนี่ยวนำของขดลวด (H)
LM
L2
L1
k
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
ลักษณะของหม้อแปลง
แกนอำกำศ
แกนเฟอร์ไรท์
แกนเหล็ก
หม้อแปลงแบบกำลังต่ำ
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
อัตรำกำรพัน
อัตรำกันพันขดลวดของหม้อแปลงหำได้จำก
n
N sec
N pri
Nsec = จำนวนขดลวดด้ำนทุติยภูมิ
Npri = จำนวนขดลวดด้ำนปฐมภูมิ
หม้อแปลงลูกหนึ่งมีจำนวนขดลวดด้ำนปฐมภูมิ 800 รอบ และมีอตั รำกำรพัน 0.25
จงหำจำนวนขดลวดด้ำนทุติยภูมิวำ่ มีกี่รอบ
200
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
ทิศทำงของกำรพัน
ทิศทำงกำรพันของขดลวดจะบ่งบอกถึงขั้วของแรงดันที่ตกคร่ อมขดทุติยภูมิที่แปรผัน
ตำมขดปฐมภูมิ โดยจะใช้เครื่ องหมำยจุด เป็ นตัวระบุข้ วั
In phase
Electronics Fundamentals 8th edition
Floyd/Buchla
Out of phase
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
หม้อแปลงแบบ Step-up และ step-down
หม้อแปลง step-up จำนวนขดทุติยภูมิจะมำกกว่ำขดปฐมภูมิ และ n > 1
หม้อแปลง step-down จะมีจำนวนขดลวดทุติยภูมินอ้ ยกว่ำขดปฐมภูมิและ n < 1
จงหำแรงดันด้ำนทุติยภูมิ
4:1
Vpri
120 Vrms
จงหำอัตรำกำรพัน
Electronics Fundamentals 8th edition
Floyd/Buchla
?30 Vrms
0.25
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
หม้อแปลงแบบ Isolation
หม้อแปลงที่มีอตั รำกำรพันเท่ำกับ 1 เรี ยกว่ำ หม้อแปลง isolation
Isolation
transformer
1:1
120 Vac
120 Vac
หม้อแปลงแบบนี้จะป้องกันไฟ dc ระหว่ำงวงจรสองวงจร กำรที่มนั สำมำรถบล็อกไฟ dc ได้กเ็ พรำะ
ฟลักซ์สนำมแม่เหล็กจะไม่มีกำรเปลี่ยนแปลงเมื่อได้รับไฟ dc
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 114
Summary
หม้อแปลง Coupling
ใช้เป็ นตัวผ่ำนของสัญญำณควำมถี่สูงจำกสเตจหนึ่งไปยังอีกสเตจหนึ่ง
Coupling transformer
Amplifier
stage 1
ac + dc
voltage
Primary resonant circuit
Electronics Fundamentals 8th edition
Floyd/Buchla
ac
voltage
only
Amplifier
stage 2
Secondary resonant circuit
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
กระแส
หม้อแปลงไม่สำมำรถเพิ่มกำลังไฟฟ้ำได้ ดังนั้นถ้ำแรงดันที่ขดทุติยภูมิสูงกว่ำขดปฐมภูมิ
แล้ว จะทำให้กระแสที่ฝั่งทุติยภูมิมีค่ำน้อยกว่ำด้ำนปฐมภูมิ
อัตรำกำรพันของหม้อแปลง เมื่อพิจำรณำกระแส จะได้
n
Electronics Fundamentals 8th edition
Floyd/Buchla
I pri
I sec
จะเห็นว่ำกระแสด้ำนปฐมภูมิจะเป็ นตัวตั้ง
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 114
Summary
กำลังไฟฟ้ำ
โดยอุดมคติแล้วหม้อแปลงจะไม่มีกำลังไฟฟ้ำตกอยู่ หม้อแปลงจะทำหน้ำที่ในกำร
ส่ งผ่ำนกำลังไฟฟ้ำจำกแหล่งจ่ำยไปยังโหลด นัน่ คือ
Ppri  Psec
V pri I pri  Vsec I sec
Vsec I pri

V pri I sec
Electronics Fundamentals 8th edition
Floyd/Buchla
ซึ่งก็คืออัตรำกำรพัน หรื อ n นัน่ เอง
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
ค่ำควำมต้ำนทำนสะท้อน
หม้อแปลงจะเปลี่ยนทั้งแรงดันและกระแสจำกด้ำนปฐมภูมิ ไปยังด้ำนทุติยภูมิ ทำให้
ค่ำควำมต้ำนทำนโหลดที่ดำ้ นปฐมภูมิมีค่ำเปลี่ยนไปด้วย
จำกกฎของโอห์ม
R pri 
V pri
I pri
and RL 
Vsec
I sec
หำอัตรำส่ วนของ Rpri และ RL จะได้
 V pri

RL  Vsec
R pri
Electronics Fundamentals 8th edition
Floyd/Buchla
  I sec
 
  I pri

 1  1  1
 =     2
 n  n  n

© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 114
Summary
ค่ำควำมต้ำนทำนสะท้อน
ค่ำควำมต้ำนทำนที่มองเห็นจำกด้ำนปฐมภูมิน้ ีจะเรี ยกว่ำ ค่ำควำมต้ำนทำนสะท้อน
2
1
R pri    RL
n
เมื่อมองจำกด้ำนปฐมภูมิ ค่ำควำม
ต้ำนทำนโหลดจะเปลี่ยนไป
Electronics Fundamentals 8th edition
Floyd/Buchla
RL
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Impedance matching
อิมพีแดนซ์ เป็ นค่ำที่อยูใ่ นไฟ ac โดยจะรวมเอำค่ำควำมต้ำนทำน
(resistance) กับค่ำรี แอคแตนซ์ (reactance) เข้ำด้วยกัน ในกำรแมตช์ค่ำ
ควำมต้ำนทำนโหลดเข้ำกับค่ำควำมต้ำนทำนภำยในของแหล่งจ่ำยเพื่อให้ค่ำกำรส่ ง
ถ่ำยกำลังงำนสู งสุ ด จึงจำเป็ นต้องทำ Impedance Matching
Rint
Vs
RL
Impedance
matching
transformer
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Impedance matching
The balun is a specialized transformer to match a balanced line to
an unbalanced line and vice-versa (hence the name balun). A
balanced signal is composed of two equal-amplitude signals that
are 180o out-of-phase with each other. An unbalanced signal is
one that is referenced to ground. In the illustration, an unbalanced
signal is converted to a balanced signal by the balun transformer.
Unbalanced
signal
Coax
Electronics Fundamentals 8th edition
Floyd/Buchla
Balun
1:2
Balanced
signal
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Impedance matching
One common application of a balun is in matching a
balanced dipole antenna to a coax line. This is shown
in the illustration.
Balanced antenna
Beside making the conversion from a
balanced line to an unbalanced line, the
balun can also match two different
impedances. For example, a dipole
antenna of 300 W can be matched to a
75 W coax using a balun.
Electronics Fundamentals 8th edition
Floyd/Buchla
Balun
Coax cable
(unbalanced)
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Non-ideal transformers
An ideal transformer has no power loss; all power applied to the
primary is all delivered to the load. Actual transformers depart from
this ideal model. Some loss mechanisms are:
Winding resistance (causing power to be dissipated in the
windings.)
Hysteresis loss (due to the continuous reversal of the magnetic
field.)
Core losses due to circulating current in the core (eddy currents).
Flux leakage flux from the primary that does not link to the
secondary
Winding capacitance that has a bypassing effect for the windings.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Transformer efficiency
The efficiency of a transformer is the ratio of power
delivered to the load (Pout) to the power delivered to
the primary (Pin). Than is
 Pout
 Pin
 

100%

What is the efficiency of the transformer? 94%
(See next
slide for
method.)
20 mA
Vpri
120 Vrms
Electronics Fundamentals 8th edition
Floyd/Buchla
15 Vrms
RL
100 W
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Transformer efficiency
 VL 2

2


15
V


 Pout 
RL
100 W 100%  94%
 
100%  
100%  
120 V  0.020 A  
 Pin 
 Vpri  I pri  




What is the efficiency of the transformer? 94%
20 mA
Vpri
120 Vrms
Electronics Fundamentals 8th edition
Floyd/Buchla
15 Vrms
RL
100 W
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Tapped and multiple-winding transformers
Frequently, it is useful to tap a transformer to allow for a
different reference or to achieve different voltage
ratings, either on the primary side or the secondary side.
Multiple windings can be on either the primary or
secondary side. One application for multiple windings is
to connect to either 120 V or 240 V operation.
Secondary with center-tap
Electronics Fundamentals 8th edition
Floyd/Buchla
Primary with multiple-windings
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Tapped and multiple-winding transformers
Transformer
7200 V
120 V
CT Ne
utral
120 V
Utility companies frequently use multiple-tapped
transformers. By selecting different taps, on the
primary side, the voltage delivered
Service
entrance
to the customer can be adjusted.
The center-tapped
Building
secondary allows
household wiring to
select either 120 V or
120 V
240 V, depending on
240 V
120 V
the circuit.
Distribution
or breaker box
Earth
ground
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Summary
Three-phase transformers
Three-phase power is used for power transmission and industrial
applications. Voltages in a three-phase system can be transformed with
three identical single phase transformers or by one three-phase
transformer. Three-phase transformers are wired in either a wye or a
delta configuration or a combination of both. The names refer to the
typical schematic representation of the windings. Three-phase
This transformer is a wye-todelta configuration, which is
generally used in step down
cases. The delta-wye (not
shown) is generally used in
step up cases.
Electronics Fundamentals 8th edition
Floyd/Buchla
wye to delta
transformer
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Selected Key Terms
Mutual The inductance between two separate coils, such
inductance as in a transformer.
Transformer An electrical device constructed of two or more
coils that are magnetically coupled to each
other so that there is mutual inductance from
one coil to the other.
Primary The input winding of a transformer; also
winding called primary.
Secondary The output winding of a transformer; also called
winding secondary.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Selected Key Terms
Magnetic The magnetic connection between two coils as
coupling a result of the changing magnetic flux lines of
one coil cutting through the second coil.
Turns ratio The ratio of the turns in the secondary
winding to the turns in the primary winding.
Reflected The resistance of the secondary circuit
resistance reflected into the primary circuit.
Impedance A technique used to match a load resistance to a
matching source resistance in order to achieve maximum
transfer of power.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
1. The measurement unit for the coefficient of coupling is
a. ohm
b. watt
c. meter
d. dimensionless
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
2. A step-up transformer refers to one in which
a. the voltage across the secondary is higher than
the primary.
b. the current in secondary is higher than the
primary.
c. the power to the load is higher than deleivered to
the primary.
d. all of the above.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
3. An isolation transformer
a. blocks both ac and dc.
b. blocks ac but not dc.
c. blocks dc but not ac.
d. passes both ac and dc.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
4. If the current in the secondary is higher than in the
primary, the transformer is a
a. a step-up transformer.
b. an isolation transformer.
c. a step-down transformer.
d. not enough information to tell.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
5. An ideal transformer has
a. no winding resistance.
b. no eddy current loss.
c. power out = power in.
d. all of the above.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
6. Assume a step-down transformer is used between a
source and a load. From the primary side, the load
resistance will appear to be
a. smaller.
b. the same.
c. larger.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
7. A transformer that can deliver more power to the load
than it receives from the source is a(n)
a. step-up type.
b. step-down type.
c. isolation type.
d. none of the above.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
8. Generally, the purpose of an impedance matching
transformer is to
a. make the load voltage appear to be the same as
the source voltage.
b. make the load resistance appear to be the same as
the source resistance.
c. make the load current appear to be the same as
the source current.
d. provide more power to the load than is delivered
from the source.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
9. A type of transformer that tends to not be ideal because it
is designed for a good frequency response is a
a. step-up type.
b. step-down type.
c. isolation type.
d. impedance matching type.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
10. A transformer that could be used for 110 V or 220 V
operation is a
a. multiple-winding type.
b. center-tapped type.
c. isolation type.
d. all of the above.
Electronics Fundamentals 8th edition
Floyd/Buchla
© 2010 Pearson Education, Upper Saddle
River, NJ 07458. All Rights Reserved.
Chapter 14
1
Quiz
Answers:
Electronics Fundamentals 8th edition
Floyd/Buchla
1. d
6. c
2. a
7. d
3. c
8. b
4. c
9. d
5. d
10. a
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River, NJ 07458. All Rights Reserved.