二极体二极体  文件类型：PDF/Adobe Acrobat   文件大小：字节

1
Ch3 DiodesCh3 Diodes
二极体二极体
主讲: 明峰副教授主讲: 明峰副教授
明新科技大学电子工程系明新科技大学电子工程系
EE--mail : mflu@must.edu.twmail : mflu@must.edu.tw
明新科技大学电子系 明峰2
Outline 大纲
3.1 ( 想二极体)
3.2 (接面二极体的端点特性)
3.3 (二极体顺偏特性之模型化)
3.4 (反偏崩溃区的操作-齐纳二极体)
3.5 (整 器电 )
3.6 (限制及箝位电 )
3.7 (二极体的物 操作)
3.8 (特殊二极体 型)
2
Figure 3.1 The ideal diode: (a)diode circuit symbol; (b)i-vcharacteristic; (c)
equivalent circuit in the reverse direction; (d)equivalent circuit in the forward direction.
想二极体
Cut off Turn on
Piecewise linear
model
明新科技大学电子系 明峰4
外接电 的设计
必须能够限制通
过导通二极体的
顺向电 ,以及
跨在截止二极体
上之逆向电压.
Figure 3.2 The two modes of operation of ideal diodes and the use of an external
circuit to limit the forward current (a)and the reverse voltage (b).
外接电
3
Figure 3.3 (a)Rectifier circuit. (b)Input waveform. (c)Equivalent circuit when vI≥0.(d)Equivalent
circuit when vI≤0. (e)Output waveform. (Ex:3.1) transfer function. (Ex: 3.2) waveform of vD.
Rectifier整 器
明新科技大学电子系 明峰6
Figure 3.4Circuit and waveforms for Example 3.1.
Ex: 3.1
4
明新科技大学电子系 明峰7
Figure 3.5Diode logic gates: (a)OR gate; (b)AND gate (in a positive-logic system).
二极体 辑闸
Y=A+B+C
Y=A.B.C
明新科技大学电子系 明峰8
Figure 3.6 Circuits for Example 3.2.
Ex: 3.2
5
明新科技大学电子系 明峰9
Outline 大纲
3.1 ( 想二极体)
3.2 (接面二极体的端点特性)
3.3 (二极体顺偏特性之模型化)
3.4 (反偏崩溃区的操作-齐纳二极体)
3.5 (整 器电 )
3.6 (限制及箝位电 )
3.7 (二极体的物 操作)
3.8 (特殊二极体 型)
明新科技大学电子系 明峰10
Figure 3.7The i-vcharacteristic of a
silicon junction diode.
Figure 3.8 The diode i-vrelationship with some scales
expanded and others compressed in order to reveal details.
二极体i-v特性曲线
6
明新科技大学电子系 明峰11
i-v特性曲线
IS: saturation current or scale current
温 每上升5℃,IS其值将加倍
温 每上升10℃, 逆向电 将加倍
VT: thermal voltage
室温下VT= 25mV
n: ideality factor
n = 1~2
Cut-in voltage~ 0.7V
)1(/ =TnVv
SeIi
q
kT
VT=
明新科技大学电子系 明峰12
Figure 3.9 Illustrating the temperature dependence of the diode
forward characteristic. At a constant current, the voltage drop
decreases by approximately 2 mV for every 1°C increase in
temperature.
温 效应
1
2
12
1
2
12
/
log3.2
ln
ln
I
I
nVVV
I
I
nVVV
I
i
nVv
eIi
T
T
S
T
nVv
S
T
=
=
=
≈
7
明新科技大学电子系 明峰13
Outline 大纲
3.1 ( 想二极体)
3.2 (接面二极体的端点特性)
3.3 (二极体顺偏特性之模型化)
3.4 (反偏崩溃区的操作-齐纳二极体)
3.5 (整 器电 )
3.6 (限制及箝位电 )
3.7 (二极体的物 操作)
3.8 (特殊二极体 型)
明新科技大学电子系 明峰14
Figure 3.10A simple circuit used to
illustrate the analysis of circuits in
which the diode is forward conducting.
指 模型
一组有2个未知 ID和VD的
方程式
There are 3ways to solve a
nonlinear circuit:
图解法(Graphical analysis)
叠代法(Iterative or Analytical
analysis)
Solving with models
R
VV
I
eII
DDD
D
nVV
SD
TD

=
=/
8
明新科技大学电子系 明峰15
The graphical method is only useful for DC.
负载线(load line)和二极体特性曲线交於Q点(operating
point) ,求出ID和VD的值
Figure 3.11Graphical analysis of the circuit in Fig. 3.10 using the exponential diode model.
指 模型的图解分析
明新科技大学电子系 明峰16
指 模型的叠代分析
Ex: 3.4
The circuit eq.
The characteristic eq. for the
nonlinear device
A transcendental equation
Figure 6-3A nonlinear circuit.
(6.4)OIDSvviR=
()1 (6.5)DTvnV
DSiIe=
)1(/ =TonVv
SSIoeRIvv
9
Figure 3.13Piecewise-linear model of
the diode forward characteristic and its
equivalent circuit representation.
片段线性模型及等效电
00
0
,/)(
,0
DDDDDD
DDD
VvrVvi
Vvi
≥ =
≤=
Figure 3.12 Approximating the diode
forward characteristic with two straight
lines: the piecewise-linear model.
=
=
20
65.00
D
D
r
VV
The straight-line approximation
can be modeled as a resistor
Figure 3.15 Development of the constant-voltage-
drop model of the diode forward characteristics. A
vertical straight line (B) is used to approximate the
fast-rising exponential. Observe that this simple
model predicts VDto within ±0.1 V over the
current range of 0.1 mA to 10 mA.
定电压 模型及等效电
Figure 3.16The constant-voltage-drop
model of the diode forward
characteristics and its equivalent-circuit
representation.
10
明新科技大学电子系 明峰19
想二极体模型
完全忽 二极体的压
明新科技大学电子系 明峰20
小信号模型
直 偏压
瞬时值
TDnVV
SDeII/=
Figure 3.17Development of the diode small-signal model.
Note that the numerical values shown are for a diode with n = 2.
dD
d
T
D
D
T
d
D
nVv
D
nVvnVV
S
nVvV
S
nVv
SD
dDD
iI
v
nV
I
I
nV
v
I
eIeeI
eIeIti
tvVtv
TdTdTD
TdDTD
+=
+=





+≈
==
==
+=
+
1
)(
)()(
///
/)(/
11
明新科技大学电子系 明峰21
Small-signal Resistance
A diode can be replaced by a small-signal(or
incremental增 电阻) resistance rdor a
conductance gd.
Notice the model is a function of the bias point.
T
D
DDT
nVv
S
D
D
dnV
I
VvnV
eI
piontQdV
di
g
TD
=
=
==
@@
/
D
T
d
dI
nV
g
r==
1
明新科技大学电子系 明峰22
Ex: 3.6
Figure 3.18 (a)Circuit for Example 3.6. (b)Circuit for calculating the dc operating
point. (c)Small-signal equivalent circuit.
12
明新科技大学电子系 明峰23
Figure 3.19Circuit for Example 3.7.
二极体顺偏稳压电
电
图形
小信号 想二极
体
定电压 片段线性指 模型
Table 3.1 Modeling the Diode Forward Characteristic
13
明新科技大学电子系 明峰25
Outline 大纲
3.1 ( 想二极体)
3.2 (接面二极体的端点特性)
3.3 (二极体顺偏特性之模型化)
3.4 (反偏崩溃区的操作-齐纳二极体)
3.5 (整 器电 )
3.6 (限制及箝位电 )
3.7 (二极体的物 操作)
3.8 (特殊二极体 型)
明新科技大学电子系 明峰26
崩溃二极体(breakdown diode)或齐
纳二极体(Zener diode)
操作在二极体反向崩溃区的电压稳压器
温 系 TC(temco)
VZ小於5V之TC值为 至负
较高VZ电压之TC值为正
常用2mV/℃之正温 系 之齐纳二极体
与-2mV/℃之顺偏二极体 ,得到低温
系 之(VZ+0.7) 考电压
Figure 3.20Circuit symbol for
a Zener diode.
反偏崩溃区之操作
14
Figure 3.22 Model for the zener diode.
Model for the Zener Diode
ZZZZIrVV+=0
Figure 3.21 The diode i-vcharacteristic with
the breakdown region shown in some detail.
rZ: 增 电阻或动态电阻
(dynamic resistance)
明新科技大学电子系 明峰28
Figure 3.23 (a)Circuit for Example 3.8. (b)The circuit with the zener diode
replaced with its equivalent circuit model.
Shunt Regulator (分 稳压器)
Ex: 3.8
15
明新科技大学电子系 明峰29
Outline 大纲
3.1 ( 想二极体)
3.2 (接面二极体的端点特性)
3.3 (二极体顺偏特性之模型化)
3.4 (反偏崩溃区的操作-齐纳二极体)
3.5 (整 器电 )
3.6 (限制及箝位电 )
3.7 (二极体的物 操作)
3.8 (特殊二极体 型)
明新科技大学电子系 明峰30
功 变压器(power transformer)的主要线圈具有N1
圈,次要线圈具有N2圈.
一个5V的直 输出需要8Vrms的次级电压,可用15:1的圈 比
达成.
Figure 3.24Block diagram of a dc power supply.
整 器电
16
半波整 器
Figure 3.25 (a)Half-wave rectifier. (b)Equivalent circuit of the half-wave rectifier with the
diode replaced with its battery-plus-resistance model. (c)Transfer characteristic of the
rectifier circuit. (d)Input and output waveforms, assuming that rD<<R.
RrifVvv
VvVv
rR
R
v
Vvv
DDSO
DSDS
D
O
DOO
<T.
The diode is assumed ideal.
波电压
fC
I
fCR
V
CR
T
V
RCTV
eV
eVVV
Lp
p
p
RCT
p
RCT
ppr
===
=
=
=


)]/1(1[
)1(/
/
明新科技大学电子系 明峰36
Peak Detector峰值侦测器
Figure 3.30Waveforms in the full-wave peak rectifier.
fCR
V
Vp
r2
=
19
明新科技大学电子系 明峰37
Taylor-series Expansion
Small-signal approximation = first term of Taylor-series
expansion
The Taylor-series expansion of exponential
L++++=
!3!2
1
32xx
xex
])(
6
1
)(
2
1
1[
)1(
32
///
/)(//
L++++=
==
=≈ =+
T
d
T
d
T
d
D
nVv
D
nVvnVV
S
nVvV
S
nVv
S
nVv
SD
nV
v
nV
v
nV
v
I
eIeeI
eIeIeIi
TdTdTD
TdDTDTD
d
d
T
d
D
T
d
T
d
T
d
D
DDd
r
v
nV
v
I
nV
v
nV
v
nV
v
I
Iii
=≈
+++=
=
])(
6
1
)(
2
1
[32L
明新科技大学电子系 明峰38
Figure 3.31 The "superdiode" precision half-wave rectifier and its almost-ideal
transfer characteristic. Note that when vI> 0 and the diode conducts, the op amp
supplies the load current, and the source is conveniently buffered, an added advantage.
Not shown are the op-amp power supplies.
密半波整 器-超级二极体
20
明新科技大学电子系 明峰39
Outline 大纲
3.1 ( 想二极体)
3.2 (接面二极体的端点特性)
3.3 (二极体顺偏特性之模型化)
3.4 (反偏崩溃区的操作-齐纳二极体)
3.5 (整 器电 )
3.6 (限制及箝位电 )
3.7 (二极体的物 操作)
3.8 (特殊二极体 型)
明新科技大学电子系 明峰40
限制器(Limiter)剪除器(Clipper)
Figure 3.32General transfer
characteristic for a limiter circuit.
Figure 3.33Applying a sine wave to a limiter
can result in clipping off its two peaks.
KLvLv
KLvKLKvv
KLvLv
IO
IIO
IO
/,
//,
/,
++
+

>=
≤≤=
<=
21
明新科技大学电子系 明峰41
Figure 3.34Soft limiting.
Soft Limiting
限制器
双重限制器
单一限制器
硬限制器
软限制器
Figure 3.35A variety of basic limiting circuits.
22
明新科技大学电子系 明峰43
DC Restorer 直 还原器
Figure 3.36The clamped capacitor or dc restorer with a square-wave input and no load.
CIOvvv+=
明新科技大学电子系 明峰44
Figure 3.37The clamped capacitor with a load resistance R.
The Clamped Capacitor with R
23
明新科技大学电子系 明峰45
Figure 3.38Voltage doubler: (a)circuit; (b)waveform of the voltage across D1.
Voltage Doubler倍压器
明新科技大学电子系 明峰46
Outline 大纲
3.1 ( 想二极体)
3.2 (接面二极体的端点特性)
3.3 (二极体顺偏特性之模型化)
3.4 (反偏崩溃区的操作-齐纳二极体)
3.5 (整 器电 )
3.6 (限制及箝位电 )
3.7 (二极体的物 操作)
3.8 (特殊二极体 型)
24
明新科技大学电子系 明峰47
Figure 3.39Simplified physical structure of the junction diode. (Actual geometries
are given in Appendix A.)
Figure 3.40 Two-dimensional
representation of the silicon crystal. The
circles represent the inner core of silicon
atoms, with +4 indicating its positive charge
of +4q, which is neutralized by the charge of
the four valence electrons. Observe how the
covalent bonds are formed by sharing of the
valence electrons. At 0 K, all bonds are
intact and no free electrons are available for
current conduction.
Figure 3.41At room temperature, some of
the covalent bonds are broken by thermal
ionization. Each broken bond gives rise to a
free electron and a hole, both of which
become available for current conduction.
25
Figure 3.43 A silicon crystal doped by a
pentavalent element. Each dopant atom donates
a free electron and is thus called a donor. The
doped semiconductor becomes n type.
Figure 3.44 A silicon crystal doped
with a trivalent impurity. Each dopant
atom gives rise to a hole, and the
semiconductor becomes ptype.
明新科技大学电子系 明峰50
Figure 3.45 (a)The pnjunction with no applied
voltage (open-circuited terminals). (b)The potential
distribution along an axis perpendicular to the
junction.
Figure 3.46The pnjunction excited by
a constant-current source I in the
reverse direction. To avoid breakdown, I
is kept smaller than IS. Note that the
depletion layer widens and the barrier
voltage increases by VRvolts, which
appears between the terminals as a
reverse voltage.