Transcript Chapter 8

Chapter 8. Transistor bias
2015-04-07
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 8-1. VDB (Voltage-Divider Bias)
V BB 
R2
R1  R 2
 V CC
V E  V BB  V BE
IE 
VE
RE
(βdc 에 무관)
IC  IE
V C  V CC  I C R C
V CE  V C  V E
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 8-2. Accurate VDB Analysis
R TH  R 1 llR
RTH
부하선
VTH
I B  R TH  V BE  I E  R E  V TH
I E  (RE 
IE 
 dc
V TH  V BE
RE 
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R TH
R TH
 dc
)  V TH  V BE
2

L .L 
R1  R 2
V TH 
R1  R 2
V CC  V CE
RC  R E
보통 R2<R1 이므로 RTH
 R E  100 
R TH
 dc
R2
R1  R 2
I C ( sat ) 

 V CC
V CC
RC  R E
R2
R TH  ( 0 . 01 )  R E   dc
R 2  ( 0 . 01 )  R E   dc
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 8-3. VDB Load Line and Q point
① IE 
1 . 1V
②
1 . 1V
IE 
③ IE 
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 1mA
1k
 0 . 5 mA
2 .2 k
1 . 1V
510 
(for RE = 1k)
(for RE = 2.2k)
* Q Variation points
: VCC, R1, R2, RC
* But RE → Simple Variations
 2 . 15 mA
(for RE = 510Ω)
of Q point
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 8-4. Two-supply Emitter Bias
① IE 
V EE  V BE
RE
(V BE  I E R E  V EE  0 )
+
VBE
②
I B R B  V BE  I E R E  V EE  0
-
IE 
V EE  V BE
(RE 
R E  100 
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RB
 dc
RB
 dc
)
R B  0 . 01   dc  R E
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ex )
V BE   0 . 7  (  2V )  1 . 3V
IE 
1 . 3V
 1 . 3 mA
1k
 V C  10 V  (1 . 3 mA )( 3 . 6 k )  5 . 32 V
V CE  V C  V E  5 . 32 V  (  0 . 7V )  6 . 02 V
* Simplify
V C  V CC  I C  R C
VB  0
IE 
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V EE  0 . 7V
RE
V CE  V C  0 . 7V
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 8-5. Other Types Biasing
① Base Bias
Switching
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② Emitter-feedback Bias
( 고찰 )
VCC
RB
RC
βdc (大) → IC (大) → VRE (大)
→ VRB (小) → IB (小)
→ IC (小) → βdc (감소)
RE
(a)
IC 
V CE  I E  R E  I C  R C  V CC
(b) βdc 영향
V BE  I B  R B  I E  R E  V CC
 IC 
V CC  V CE
RC  R E
(I E  IC ,
IB 
V CC  V BE
(RE 
RB
 dc
)
if )
R E 
RB
 dc
(I E  IC )
IC
 dc
)
→ βdc 영향 무시가능
* βdc 의 3 : 1 변화는 IC 를 거의 3 : 1 로 변화시킴
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ex 8.6 )
 V 
2



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I 
R2
R1  R 2
 V EE
( VRL )

VC  I E  RC

V B  10 V  V 2
V EE
R1  R 2
V E  V 2  0 . 7V
IE 
VE
( VRE )
 V   10 V  V
E
E
RE
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I 
10 V
 0 . 82 mA
12 . 2 k
( VR2 )
V 2  ( 0 . 82 mA )  2 . 2 k  1 . 8V
( VRE )
V E  1 . 8  0 . 7  1 . 1V
IE 
1 . 1V
 1 . 1mA
1k
V C  (1 . 1mA )  ( 3 . 6 k )  3 . 96 V
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(Base - GND)
V B  10 V  1 . 8V  8 . 2V
(Emitter - GND)

V E  10 V  1 . 1  10 V  V E
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③ Collector-feedback Bias (or self-bias)
* βdc
IB + IC
less
3 : 1 → IC 2 : 1
βdc (大) → IC (大) → VRC (大) → VRB (小)
→ IB (小) → IC 감소
IB
IC
* V CE  ( I B  I C )  R C  V CC
IC 
V CC  V CE
포화전류 :
RC
V CC
RC
차단전압 : V CC
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* βdc 영향
V BE  I B
IC 
0
 R B  ( I B  I C )  R C  V CC
V CC  V BE
RC 
RB
→
 dc
R B  R C  dc
+
+
0.7 - -
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포화점에 달할 수 없다
0.7 >
로 하면
(IC 
V CC  V BE
)
부하선의 중앙점
2 RC
( 포화점에 달할 수 없다 )
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④ Collector-AND Emitter-feedback Bias
IE 
V CC  V BE
RC  R E 
RB
 dc
VE  IE  RE
V B  V E  0 . 7V
V C  V CC  I C  R C
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 8-7. PNP Tr
VCB +
VBE +
-
① npn Tr → pnp Tr 로 교체
VCE
+
② 전류, 전압을 모두 역으로
-VCC
동일
+VEE
+
V2
I
VB
VE’
IE +
VE (VRE)
-
VC
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