Transcript Electronics

Overview:
the Property of Oneway Conduction of diodes
Electronics
1. forward bias（P is positive and N is nagative）
the current flow is significant
2. reverse bias（ P is nagative and N is positive ）
the current flow is very small
3. No any one-way conduction when diodes
work beyond U BK
4. Reverse current flow will be influnced by
temperature.
5.The property of saturation of reverse
current flow.
Chapter6 Sources of Stable DC
Voltage(Page 167)
1. Diode Rectifiers
2. Power Supply Filtering
3. Voltage Regulator
Electronics
Sources of Stable DC Voltage
Electronics
The small power supply
Transformer
Rectifier
Regulator
Filter
Load
u1
AC
u2
u3
u4
uo
DC
1. Diode Rectifiers
• Half-Wave Rectifier
• Full-Wave Bridge Rectifier
Electronics
Electronics
Half-Wave Rectifier
Tr a
+
u
–
b
D io
RL
动画
+
uo
–
u
2U
O
t
uo
2U
O
?To calculate the average value of
output voltage
t
U o  0.45U
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Full-Wave Bridge Rectifier
a
+
u
－–
b
4
3
1
2
动画
io
u
+ 
uo RL
– －
2U
t
uo
2U
t
Positive half cycle,D1\D3
conduct,D2\D4 are reverse biased
?To calculate the average value of
output voltage
U o  0.9U
Full-Wave Bridge
Rectifier
Common
anode
– u +
o
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D1 D3 D5
io
a
RL
b
C
+
uo
–
D2 D4 D6
Common
cathode
u:The transformer secondary voltage
u
o
2
Electronics
D1 D3 D5
u a u b uC

动画
– u +
t
uo Output voltage
io
a
b
o
RL
C
D2 D4 D6
From time t1~t2 :
o
uo=uab
t1 t2 t3 t4 t5 t6 t7 t 8 t9 t
+
uo
–
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u
o
uo
o
D1 D3 D5
u a u b uC

2
– u +
t
负载电压
t1 t2 t3 t4 t5 t6 t7 t 8 t9 t
o
a
b
io
RL
c
+
uo
–
D2 D4 D6
U o  2.34U
Homework
Electronics
• To calculate the average value of output
voltage in half and full-wave rectifier circuits.
• To calculate the average value of current of
every diode in half and full-wave rectifier
circuits
• To calculate the maximum reverse bias voltage
that every diode endures in half and full-wave
rectifier circuits
2.Power Supply Filtering
~
+
u
–
+
C RL
C: Smoothing Capacitor
+
uo
–
Electronics
2.Power Supply Filtering
a
+
u
–
b
io
D i
+
C
ic
RL
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动画
u
2U
+
O
uo = u C
uo
–
t
2U
O
T
τ  RLC  (3  5)
2
(T — the period of voltage)
t
Electronics
Ipeak
RLC is larger the
uo
peak valure of iD is larger 2U
O
To choose diodes:
IOM =2 ID
iD
O
t
t
3. Voltage Regulator
• Zener Diode Shunt Regulator
• Voltage Regulator
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Zener Diode Shunt Regulator
IR R
+
u
–
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IO
Iz
+
+
+
C UI DZ
RL UO
–
–
Stable voltage
circuit
I
UZ
U
Zener Diode(Page 11)
I
UZ
U
Electronics
• UZ(2CW13:5~6.5V)
• Voltage stable constant
(Page 12)
Figure 1.3.2
Zener Diode Shunt Regulator(Page 176)
IR R
+
u
–
IO
Iz
+
+
+
C UI DZ
RL UO
–
–
to assume RL is changed
UO = UZ
UO +UR= UI
IR = I O + I Z
Stable voltage
UZ
circuit
RL(IO) IR  UO (UZ )  IZ 
UO   IR (IRR) 

Electronics
I
U
Zener Diode Shunt Regulator(Page 177)
there are four parts.
T
+
Ui
–

+
UB
–
+
R3
–
+
+
UZ
–
R1 R1
+R1
DZUf
–
R2
+
RL UO
–
reference
regular
amplifier
sample
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Electronics
T
+
Ui
–
output

+
UB
–
+
UO  UB
R3
–
+
+
UZ
–
R1 R1
+R1
DZUf
–
R1
 (1 
)U Z
R1  R 2
R2
+
RL UO
–
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IC Voltage Regulator
Three
points
Positive output
The constant voltage
78XX
output
negative output
79XX
Flexible voltage
output
（1. 25 ~ 37 V ）
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Introduction of points
2 —output
3 —common
1—input
W7800
2 —output
3—input
1 — common
W7900
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(1) constant voltage output
1
+
Ui
W7805
3
Ci
0.1~1F
_
To imorove the wave
2
+
CO
1F
UO
_
UinputUoutputis
more than
3V
To improve transiet
output
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(2)Both positive and negative voltage
output
1
2
+15V
W7815
CO
+
3
C
24V
i
C
1F
1000F 0.33F
220V
24V
+
C
1000F
Ci
1
W7915
CO
0.33F
3
1F
2
– 15V
?
• What is significant as a voltage source?
Electronics