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Lecture 16
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DC Motor Direction Control
• Half Bridge– 2 switches and 2 power sources
• H-Bridge– 4 switches and 1 power sources
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Half Bridge 1
Switch
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Half Bridge 1
Switch
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Half Bridge 2
NPN BJT
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H-Bridge 1
Switch
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H-Bridge 2
Switch
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H-Bridge 3
Switch
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H-Bridges with NPN BJT 1
Pin5 Pin6 Motor Notes
High Low forward
Low High backward
Low Low No motion
High* High* * Forbidden
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H-Bridges with NPN BJT 2
NPN NPN
PNPPNP
TIP42: PNP
TIP120: NPN
12V
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H-Bridge : How It Works
Set High
Set Low
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H-Bridge : How It Works
Set High
Set Low
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H-Bridges with Relays
Motor
+12V
Vss
1k
2N3904
2N3904Relay Relay
Relay
2N3904
Vss
Vss Vss
0.01
uF
0.01
uF
0.01
uF
Vdd Vdd
Vdd1k Relay
2N3904
Vss
0.01
uF
Vdd
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H-Bridge ICs• LMD 18200• LMD 18201• LM 15200
• SN754410NE
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Micro Dual Serial Motor Controller
• Using one serial output from the BASIC Stamp module, this motor controller can independently set each motor to go forward or backward at any of 127 speeds.
• To control additional motors, you can connect multiple motor controllers to the same serial line.
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H-Bridge Experiments
StampWorks
Others
Robotics
Earth measurements
Basic A and DWhat’s micro controller
ChaptersExperiments
Lecture 17
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Linear Differential Equation
ubtdudb
dtudb
yadtyda
dtyda
m
m
mmm
n
n
nn
n
m
n
01
1
1
01
1
1
+⋅⋅⋅++
=+⋅⋅⋅++
−
−
−
−
−
−
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First-Order Systemn >= m, n = 1 uya
dtdya =+ 01
Applying Laplace Transform
1
1
)()( 0
+=sa
sUsY
τ=>
0
0
1
))0(()(
aAy
aa
yeyytyt
=
=
+−=
∞
∞
−
∞
τ
τ
u(t) = A for t>=0u(t) = 0 for t<0
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Passive RC Low-Pass Filter
R
C
+
Vo
-
+
Vi
-
11
)()(
+=RCssV
sV
i
o
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Bode Plot• Bode plot is a very
useful graphical approach is to analyze and design feedback loops.
• It consists of plotting two curves, the log of gain, and phase, as functions of the log of frequency.
)j(
dB)VVlog(20)j(Le|)j(G|)j(G
)j(V)j(V)j(G
js)s(V)s(V)s(G
i
o
)(ji
o
i
o
ωϕ
=ω
ω=ωωω=ω
ω=
=
ωϕ−
L(jω) is log of gain, unit is dBφ(jω) is phase
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Bode Plot of Low-Pass Filter
Cutoff frequency
-3dB
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• Cut off frequency is the frequency that the power of the output signal is attenuated to half of its input value
dBdB
PiPo
AiAo
321log20
707.021
10 −==
≈==
RC
RCRC
jGPP
RCjG
RCjjG
sVsVsG
Example
c
c
ci
o
c
i
o
11)(2
1)(1
21|)(|
21
1)(1|)(|
11)(
)()()(
:
2
22
2
=
+==>
+===
=+
=
+=
=
ω
ωω
ω
ωω
ωω
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Passive RC High-Pass Filter
R
C +
Vo
-
+
Vi
-
1)()(
+=RCsRCs
sVsV
i
o
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Bode Plot of High-Pass Filter
Cutoff frequency
-3dB
