Dependent Sources in Pspice - PCC

Dependent Sources in Pspice
Independent sources in spice simulators can easily be found. They use V or I element names (VDC, IAC,
etc). This is not true of dependent sources. These sources use less obvious element names. You need
to know what you are looking for to hook up the right source.
Independent source names:
• Exxx : Voltage-controlled Voltage source (VCVS)
• Fxxx: Current-controlled Current source (CCCS)
• Gxxx: Voltage-controlled current source (VCCS)
• Hxxx: Current-controlled Voltage source (CCVS)
•
Neither Pspice nor Ltspice use diamonds to symbolize these elements. Pspice uses boxes with a circle
to indicate the output source and an arrow or +/- symbols on the controlling side. Ltspice uses the
independent source circle. So be careful when looking at your circuit, especially in Ltspice.
To use these elements you place them in your circuit like you would a normal source. Make sure the +/-
or current arrow are hooked up correctly, for the source part of the element (output). The input/control
is hooked up similar to if you were using a DMM.
So if you have a voltage controlled source the control would be hooked up as if you were measuring
voltage using a DMM. You connect the control nodes in parallel. Hook up the + control terminal to the
+ control voltage. The – control terminal is connected to the – control voltage. E1 in both Figure 1 and
Figure 2 shows how to hook up a current controlled source. Notice how both the VCVS in both
programs is a 4 terminal device. Pay special attention to the input and output terminals of these
devices.
Current controlled sources are not as easy. You must hook these up as if they are an ammeter, in
series. Pspice uses 4 terminal devices see H1 in Figure 1. Notice that the circuit branch that contains
the controlling current has been broken and it is wired to the current inputs of H1. When doing this
make sure the arrow on H1 matches your reference arrow in the schematic. When you netlist this
circuit, pspice will actually insert a 0V voltage source into your circuit where the current control is
measured.
Ltspice uses 2 terminal devices for its current controlled sources. For Ltspice, there must be an
independent voltage source in the branch that contains its controlling current. If a source does not
naturally exist in that branch then you need to insert a 0V source and use it as the reference current for
the source. In order to specify which source controls H1 in Figure 2, right click on the dependent source.
Then click on Value, and enter the name of the controlling source. In Figure 2 this is V1.
The last step is to specify the gain. In Pspice this is done by doubling clicking on the element. You must
find the variable labeled gain and enter the gain here. I would recommend setting this variable to
visible. Notice in Figure 1 that this is not the same as E or H, it is a separate variable. A common
mistake is to click on the E and change that to the gain. This does not work.
The gain in Ltspice is Value for a voltage controlled source and it is Value2 in a current controlled source.
These are found by right clicking on the element. Notice in Figure 2 that the gain for H1 is -7 and not +7.
This is because of the passive sign convention. The controlling source is V1 and the passive sign
convention would have a positive current flowing into the positive terminal of V1. This is the opposite
of the reference direction desired. A negative gain is the same as changing the current direction
reference.
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Dependent Sources in Pspice
Other references and thoughts:
I really recommend getting some sort of simple Spice reference manual.
Listing of possible PSPICE books from Powells :
http://www.powells.com/s3?kw=spice&start=1&vaguesection=Electricity
The books $

Figure 2 Mesh Example 2 in Ltspice
Dependent Sources in Pspice
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