Transcript Embedded Systems Analog Electronics

Embedded Systems
Transistors
Laboratory for Perceptual Robotics – Department of Computer Science
Bipolar Transistor
C
E
B
C
B
N
P N
C
NPN
B
E
PNP
E
NPN rules:
1. The collector must be more positive than the emitter
2. B-E and B-C behave like diodes
• B-E forward biased
• B-C reverse biased
3. Limitations on IC, IB, and VCE
4. When rules (1)-(3) are obeyed,
iC governed by
IC=hFEIB=IB
transistor action
hFE (current gain) ~ 100
Laboratory for Perceptual Robotics – Department of Computer Science
Bipolar Transistor
E
B
N
C
P N
small IC
+
+
large ICE
Laboratory for Perceptual Robotics – Department of Computer Science
Transistor Action
E
B
N
P N
B
forward biased
C
C
IC=IB
reverse biased
E
Laboratory for Perceptual Robotics – Department of Computer Science
Transistor Saturation
10 V
switch closes:
lamp
0.1A
10 V
1K
C
B
VBE=0.6V
IB=9.4V/1K=9.4mA
ICE=(IB)=100(9.4)
E
=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.
Laboratory for Perceptual Robotics – Department of Computer Science
Emitter-Follower
VE = VB-0.6V
when Vin > 0.6V
•
big current/power gain at
Vout=Vin-0.6V
•
impedance buffer
Vin
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Vout
Power Transistors
•
Darlington pairs
•
hFE=(hFE)2
•
TIP102/106
Laboratory for Perceptual Robotics – Department of Computer Science
Push-Pull Amplifier Stages
NPN can only “source” current
“crossover”
distortion
PNP can only “sink” current
Laboratory for Perceptual Robotics – Department of Computer Science