EEM 206
Electrical Circuits Laboratory
Spice is a very popular software to analyse the given electrical and electronics
circuits. This software, called as “pspice” is introduced by MicroSim Corporation.
This program simulates and calulates the considered circuit. A circuit must
bespecified terms of element name, element value, nodes, variables parameters, and
sources.
NODES
Node is connection point where two or more elements are connected in the circuit.
The node number to wich an element is connected are specified after the name element.
Node numbers are chosen as the integer number from 0 to 9999 (for student version).
ELEMENTS
The library of this software has lots of electrical and electronics elements, sources,
and devices. Common elements are given in Table 1. In Table 2, the unuit suffixes are
given. Thus, each element in the considered circuit is defined such as “Ra 1 2 125 OHM” .
Element
Variable
Unit
Variable
Vaule
Resistor
R
OHM
P
10-12
Capatior
C
F
N
10-9
Inductor
L
H
U
10-6
Voltage
Source
V
V
M
10-3
K
10 3
MEG
10 6
G
10 9
Current
Source
I
A
Table 1. Circuit elements
Table 2. Element vaules
TYPES of ANALYSIS
There exist three type analysis such as dc, transient and ac analysis. Once time
dome response is determined using transient analysis, (small-signal) frequency response is
found by ac analysis. It is know that, dc analysysis is used for dc model of circuit.
VOLTAGE and CURRENT SOURCES
The sources are decomposed into two types such as independent and dependent. Now, we
consider the independen sources. They can be modelled by some waveforms (see, Fig. 1).
Exponential source has exponential waveform and its symbol and code for pspice is given
as
EXP (V1 V2 TRD TRC TFD TFTC)
where, the variable definitions are given in Table 3.
Variable
Figure 1. Exponantial waveform
Meaning
Unit
Initial
V1
volt
voltage
Pulsed
V2
volt
voltage
Rise delay
TRD
seconds
time
Rise time
TRC
seconds
constant
Fall delay
TFD
seconds
time
Fall time
TFC
seconds
constant
Table 3. Model parameters of exp source
Pulse source is defined as Fig. 2 (see for detail, Table 4). The symbol and code of this
source type for pspice is given as
PULSE(V1 V2 TD TR TF PW PER)
where, the variable definitions are given in Table 4. Note that, this source is used for periodic
pulse sources.
Figure 2. Pulse waveform
Variable
V1
V2
TD
TR
TF
PW
PER
Meaning
Initial
voltage
Pulsed
voltage
Delay time
Rise time
Fall time
Pulse width
Period
Unit
volt
volt
seconds
seconds
seconds
seconds
seconds
Table 4. Model parameters of pulse source
Piecewise Linear Source
The source waveform can be descrined as point by point such that the considered
source signal is divided N points. Then, each point is defined by time and the vaule of
current/voltage at this time (Ti,Vi) , where i Є {1,2,...,N}. The symbol and code of this source
type for pspice is given as
PWL(V1 T1 V2 T2 ...... VN TN)
AC Source
This source is defined as a formula
V(t)= v0+va e-ψ(t-Ø)sin(2*pi*f(t-Ø)+(µ/360))
where, v0 denotes the offset voltage, va indicates the amplitude, f is frequency, Ø denotes
time delay, ψ indicates the damping ratio, and µ indicates the phase degree. This source is
repesented such as
SIN(v0 va f Ø ψ µ)
The Dependent Sources
There exists four types dependet source such that
Voltage controlled voltage source
E<name> N+ N- CN+ CN- <gain>
Voltage controlled current source
G<name> N+ N- CN+ CN- <gain>
Current controlled voltage source
F<name> N+ N- VN <gain>
Current controlled current source
H<name> N+ N- VN <gain>
Here, each source (element) in the circuit is defined using the connected node numbers. If a
voltage source is considered, then once the first node number (N+) denotes is positive node
and the second node number (N-) indicates negative node and if a current source is
considered, then the current direction is importans such as from N+ to N-. Note that, N+ and
N- denote the node numbers. Also, CN+ and CN- indicate the node numbers of the reference
voltage. In Pspice, the current must be defined by depending a voltage source. Thus, VN
denotes the voltage source that the considered current crosses. Finall, gain is the coeficient
value.
FILES for PSPICE
The input file whose extension is cir (circuit) is an ascii file. This file includes the
definition of the considered circuit using node number and the analysis type. Let us an
example circuit (Fig. 3). We find the voltage at the resistor R3.
Example
Vsource
1
R1
1
R2
3
R3
5
. PRINT DC V(5,0)
. END
0
3
5
0
DC 12V
100 OHM
20 OHM
30 OHM
Figure 3. Example circuit
In the example program, called as ex1.cir, the first line is detail line and PRINT and END are
command for analysis in the line whose the first character is dot. Note that, Pspice is a case
sensivitive software. After the nodes are determined, each element is defined using its node
numbers. The output file, ex.out, contains the voltage at R3. The input file must be
compalied to obtain the results such as
EX-2
EX-3
Homework:
AC ANALYSIS
Ac analysis is used to determine frequency of the given circuit. This analysis is
described as
Here, this command analyses the given circuit between FSTART (Hz) and FSTOP (Hz). This
frequency interval is divided to the number of sweep using linear/octave/decade.
Let us a circuit as
Here, if Vs(t) = 40 sin(Wt) V and the frequency interval between 100 Hz and 600 Hz.
TRANSIENT ANALYSIS
This analysis is used to determine the considered measuruments at the time interval
such that
TRAN TSTEP TSTOP, where TSTEP denotes the time incerement and TSTOP
indicates the final time. Note that, this analysis always starts at 0 sec.
MAGNETIC ELEMETS
The magnetic elements are mutual inductors (transformers). The symbol coupling is
K. The general form is given as
K<name> L<first inductor> L<second inductor> <coupling>
Let us consider a circuit
Now, we find the magnitude and phane angle of output current. This desired is constructed
such as
AC analysis
R1
1
2
0.5
L1
2
0
0.5MH
L2
0
4
0.5MH
Ka
L1
L2
0.999
R2
4
6
0.5
Ro
6
7
150
Vx
7
0
DC 0V
. AC LIN 3 60Hz 120Hz
. PLOT AC IM(Vx) IP(Vx)
. PROBE
. END
Here, PROBE is a command for plotting in Pspice. Note that, the first node is positive node
which is signed by dot for the inductorr L1 and L2.
OP-AMP
The op-amp is modelled as DC / AC model for Pspice (see, Fig. 4). However, an opamp (741) is simulated by using the library of Pspice. If DC / AC model is used, then this
model is defined as circuit such that the starting is .SUBCKT (sub-circuit like as sub-function)
and .ENDS terminates this sub-circuit.
a) DC model
b) AC model
Figure 4. DC / AC models for op-amp
Let us consider op-amp circuit as
The inverter amplifier can be wrote the input file as
. SUBCKT OPMAP 1 2 5 4
RIN
1 2 2MEG
R0
3 5 75
EA
3 4 2 1 20000
. ENDS OPAMP
. PRINT DC V(5,0)
. END
This file finds the output voltage.
REFERENCE
M. H. Rashid, “Spice for Circuit and Electronics Using Pspice,” Perntice Hall, New Jersey,
1990.