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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8
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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