Download PSPICE计算机仿真

PSpice计算机仿真
Simulation Program with Integrated Circuit Emphasis
CH4
ADDITIONAL DC ANALYSIS
附加直流分析
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4.1 Computing the Thevenin Equivalent
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戴维南等效
4.2 Sensitivity Analysis
 灵敏度分析
4.3 Simulating Resistor Tolerances
 误差电阻的仿真
4.1 Computing the Thevenin Equivalent
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The open-circuit voltage
The short-circuit current
Fig.35
Example 4
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Use PSpice to find the Thevenin
equivalent with respect to terminals a, b
for the circuit shown in Fig.35 (P29).
To compute the short-circuit current

We inserted a resistor(R2) between
nodes a and b (node 0) whose value is
10e-6. (Fig. 36)
Fig. 36
short-circuit current
Do not forget!
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F1的属性需要修改:
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选中F1元件, (粉色表示选中!)
Edit ->Properties…
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Gain项: 3 (Fig. 36a)
Fig. 36a Edit Properties
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在OrCAD Capture运行环境下:
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PSpice->Run
在OrCAD PSpice A/D Demo运行环境下:
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View->Output file (Fig. 37)
Fig. 37 output file
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The short circuit current, which is the
current through the voltage source V3,
is 2 A.
To compute the open-circuit voltage
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We have two options:
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Connect a resistor between nodes a and b,
in his case 10e6 (Fig. 38)
Connect a capacitor between nodes a and
b
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The capacitor behaves like an open circuit
during dc analysis and, therefore, does not
influence the dc Thevenin equivalent.
Fig. 38 open-circuit voltage
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OrCAD Capture环境:
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PSpice->Run
OrCAD PSpice A/D Demo环境:

View->Output file (Fig. 39)
Fig. 39 output file
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Note that node a in the original circuit
(Fig. 35) is assigned as node 54 (It may
be different with yours.) by PSpice, so
the open-circuit voltage is 12 V.
The Thevenin equivalent
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Open-circuit voltage
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Short-circuit current
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12V
2A
Therefore, the Thevenin resistance is
12/2= 6 Ω and the Thevenin equivalent
circuit is as shown in Fig. 40.
Fig. 40
Thevenin equivalent
4.2 Sensitivity Analysis(灵敏度分析)

Example 5 illustrates how to perform
sensitivity analysis to predict the
behavior of an unloaded voltage-divider
circuit(空载分压电路).
Fig. 41(P33)
Example 5

Use PSpice to study the sensitivity of
the output voltage Vo in the voltage
divider circuit shown in Fig. 41.
Fig. 42
Components
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Analog/R
Source/VDC
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注意:
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Out 为节点的名字, Place/Net Alias…
Simulation
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PSpice/New Simulation Profile (Fig. 43)
Fig.43_setting
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PSpice/Run
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PSpice/View Output File (Fig. 44)
Fig.44_Output file
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From the sensitivity data, we deduce
that
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If R1 increases by 1Ω, Vo will decrease by
0.8V, that is, Vo=99.2V
If R1 increases by 1%, Vo will decrease by
0.2V to 99.8V
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If R2 increases by 1Ω, Vo will increase
by 0.2V, that is, Vo=100.2V
If R2 increases by 1%, Vo will increase
by 0.2V to 100.2V
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If V1 increases by 1V, Vo will increase
by 0.8V, that is, Vo=100.8V
If V1 increases by 1%, Vo will increase
by 1V to 101V
Question?
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If R1 increases by 1Ω, R2 decreases by
1%, and V1 increases by 0.5V, Vo=?
Answer!
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We have a linear circuit, so the principle
of superposition (叠加原理) applies, and
therefore,
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Vo=100 - 0.8 - 0.2 + 0.4=99.4 V
4.3 Simulating Resistor Tolerances
(误差电阻的仿真)
Example6

Replace the 100Ω resistor in the circuit
in Fig.41 with a resistor having the
same value but with a 10% tolerance.
Use PSpice to discover the range of
output voltage values that you can
expect with this more realistic model of
a resistor.
Fig. 45
R2属性修改：
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选中电阻R2，(粉色表示被选中!)
单击鼠标右键，选择Edit Properties…,
Fig.45
在Tolerance项，写入“10%”, Fig. 46背
景；选中Tolerance项,单击Display按钮，
出现Fig. 46 对话框；
Fig. 46
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DC sweep analysis
Monte Carlo/Worst Case
Fig. 46a DC sweep analysis
Fig. 47 Monte Carlo/Worst Case
Fig. 48 maximum
Fig. 49 output file

You can confirm this result using the
voltage division equation for the circuit
in Fig. 41 when the R2 resistor has the
value 110 Ω.
Fig. 50 minimum
Fig. 50a output file

You can confirm this result using the
voltage division equation for the circuit
in Fig. 41 when the R2 resistor has the
value 90 Ω.

Thus, we see that when the R2 resistor
in Fig. 41 has a tolerance of 10%, the
actual output(实际输出) voltage may
range from 97.826 V to 101.85 V.