Download DC Sweep

In PSpice
DC Sweep in PSpice
 A simulation that results in a plot of
specified voltages and/or currents
in the circuit as a function of a
particular variable.
 The variables that can be swept
include the magnitude of a d.c.
voltage or current source,
temperature of the circuit (as most
materials including resistors
change their value as temperature
changes), a model parameter –
which might be the open loop gain
of an op amp, and a global
parameter, such as the magnitude
of a variable defined using the
PARAM part.
 Multiple sweeps can be performed
using the nested sweep option.
Example:
Circuit from Design a Night Light
Goal:
Perform a DC Sweep of
the voltage on the
positive input terminal of
the op amp to show how
the output voltage
changes as the value of
Vref increases from 0V to
a value larger than the
voltage on the negative
input terminal, which is
equal to the voltage
across R2.
DC Sweep
 To set up a DC sweep, open
the Analysis Setup popup
window and select DC
Sweep
 Sweep Var. Type: Voltage
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Source
Name: Vref
Sweep Type: Linear
Start Value: 0V
End Value: 9V
Increment: Should be
sufficiently small to show a
sharp transition
Selection of Increment
0.5V increment
1mV increment
These are two plots of the DC Sweep of Vref in the example circuit, where the only
difference is the value used as the increment. Ideally, there should be a sharp
transition as the output of the voltage comparator switches from one output level to
the other . However, when the increment of 0.5V was used, PSpice interpolated
between the calculated values for the output voltage of the op amp when Vref = 5V
and Vref = 5.5V. As a result, the sharp transition looks like a gradual transition – an
artifact of improper settings used during the simulation.
Markers
 A plot will be automatically generated for the node voltages
as a function of Vref wherever a voltage marker is placed in
the circuit.
 Current markers must be placed at the end of a component
– the point where the blue of the component wire meets the
green of the wire that you drew to connect the part to
another component.
 Two voltage markers, one with a + and one with a –are
placed on the schematic when Voltage Differential is
selected from the Marker toolbar. The difference in the
node voltages is displayed on the plot.
 Mark Advanced contains a set of options that include phase
angle of the voltage or current at a node.
Markers
 Voltage and current
markers are placed in the
schematic by clicking on
either:
 the Markers/Mark
Voltage/Level or
Mark/Mark Current
into Pin
 or by using the shortcut
on the toolbar.
Plotting Current and Voltage
 More than one marker can be put into a schematic.
However only one plot will be generated automatically.
 Only one scale is used per plot. If you plot the current
flowing through the diode on the same graph as the
output voltage of the op amp, the current flowing out of
the op amp will look like it is always zero because it is a
maximum of 15 mA when the scale is +/- 9V.
The green curve in the plot is the
output voltage of the op amp and
the red curve is the current
flowing out of the op amp into the
1kW resistor, Rlimit, connected to
the output of the op amp.
Rescaling Current
 Once you have a plot with
both voltage and current,
click on the key for the
current located on the
bottom left of the graph
 in this example, -I(Rlimit)
 A popup window called
Modify Trace will open.

In the Trace Expression box
at the bottom, type *1000
next to the name of the
current that is already in
the box.
Plot:
Voltage and (rescaled) Current