Embedded%20Systems%20Transistors

1
Embedded SystemsTransistors
2
Bipolar Transistor
C
C
B
PNP
E

• NPN rules
• The collector must be more positive than the
  emitter
• B-E and B-C behave like diodes
• B-E forward biased
• B-C reverse biased
• Limitations on IC, IB, and VCE
• When rules (1)-(3) are obeyed,
• IChFEIB?IB
• hFE (current gain) 100

iC governed by transistor action
3
Bipolar Transistor
C
4
Transistor Action
C
B
C
reverse biased
forward biased
IC?IB
E
5
Transistor Saturation
switch closes
?VBE0.6V
IB9.4V/1K?9.4mA
ICE?(IB)100(9.4) 940mA
to get that much current through the lamp VC
would have to go significantly below ground,
which is illegal by rule 1 The collector must
be more positive than the emitter the
transistor is saturated---only enough IC current
flows through the transistor to keep the
collector 0.05 to 0.2 V more positive than the
emitter.
6
Emitter-Follower

• VE VB-0.6V
• when Vin gt 0.6V
• big current/power gain at
• VoutVin-0.6V
• impedance buffer

Vin
Vout
7
Power Transistors

• Darlington pairs
• hFE(hFE)2
• TIP102/106

8
Push-Pull Amplifier Stages
NPN can only source current
crossover distortion
PNP can only sink current