Transistor de Junção Bipolar
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Transistor
• Três regiões dopadas: emissor, base, e
coletor
• Duas junções pn: base-emissor e basecoletor
• NPN ou PNP
• Silício o germânio
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Imagem representando o transistor de junção bipolar
N
COLETOR (dopagem média)
P
BASE (dopagem leve)
N
EMISSOR (dopagem pesada)
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Transistor polarizado
• Diodo polarizado diretamente no
emissor
• Diodo polarizado reversamente no
coletor
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Transistor currents
• A é corrente do coletor proporcional a
corrente de base, este ganho é βdc ou hFE
• O ganho de corrente é geralemente entre
100 e 300
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IC
IC
IB
IB
IE
IE
Sentido do elétron
Sentido convencional
IC @ IE
I E = IC + I B
adc =
IC
IE
bdc =
IB << IC
IC
IB
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The base circuit is usually analyzed with the
same approximation used for diodes.
VBB - VBE
IB =
RC
RB
VCE
VCC
RB
VBB
VBE
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VBB - VBE
IB =
IB =
RB
5 V - 0.7 V
= 43 mA
100 kW
RC
100 kW
VCC
RB
VBB
5V
VBE = 0.7 V
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IC = bdc IB
IC = 100 x 43 mA = 4.3 mA
100 kW
RC
bdc = 100
RB
IB = 43 mA
VBB
5V
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VCC
VRC = IC x RC
VRC = 4.3 mA x 1 kW = 4.3 V
100 kW
1 kW
IC = 4.3 mA
12 V
RB
IB = 43 mA
VBB
RC
5V
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VCC
VCE = VCC - VRC
IC = 4.3 mA
VCE = 12 V - 4.3 V = 7.7 V
100 kW
1 kW
VCE
12 V
RB
IB = 43 mA
VBB
RC
5V
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VCC
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