Lecture 3: Chapter 2, Part 1 - Classes

Lecture 3: Chapter 2, Part 1
Matthew Shuman
January 11th, 2011
1 Voltage and Current Sources — Section 1.6 in Text
1.1 Ideal Current and Voltage Sources
An ideal voltage source will supply any current to achieve the desired voltage across its two terminals.
An ideal current source will supply any voltage to achieve the desired current through its two
terminals. Figure 1 shows the LTspice symbol for a voltage source. Figure 2 shows the LTspice
symbol for a current source.
Figure 1: This is the LTspice symbol for a voltage
source
Figure 2: This is the LTspice symbol for a current
source
1.2 Dependent Current and Voltage Sources
Dependent current and voltage sources use another current or voltage in the circuit to determine
the voltage or current being output by the source. There are four total combinations of dependent
sources. Figure 3 is a current controlled current source and figure 4 is a voltage controlled current
source. Figure 5 is a current controlled voltage source and figure 6 is a voltage controlled voltage
source.
Figure 3: This is the LTspice symbol for a CCCS
Figure 4: This is the LTspice symbol for a VCCS
Figure 5: This is the LTspice symbol for a CCVS
Figure 6: This is the LTspice symbol for a VCVS
1

2 Electrical Resistance, Ohm’s Law — Section 2.2 in Text
Figure 7 shows the LTspice symbol for a resistor. A resistor is a device that is engineered to resist
the flow of current. The dimensions are controlled according to the following equations. They are
usually made out of carbon, which specifies the value of ρ.
R = ρ ∗ L
(1)
A
The relationship of voltage across and current through a resistor is stated in Ohm’s Law, which is
the following equation.
V = I ∗ R (2)
Figure 7: This is the LTspice symbol for a resistor
3 Nodes, Branches, and Loops — Section 2.3 in Text
Figure 8 is the demonstration circuit using in lecture. There is a single 1.2 volt NiCd battery in the
battery holder. The resistor is 3.3 kΩ. Figure 9 shows a LTspice schematic of this circuit.
Figure 8: This is a photo of a circuit, built using a
breadboard
Figure 9: This is a schematic in LTspice
Figure 10 shows how LTspice can simulate a circuit to solve for voltages and currents.
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Figure 10: This is a simulation output in LTSpice
4 Modeling a Bipolar Juntion Trasistor using a current dependent
current source
Figure 11 shows how a current dependent current source can be modeled in LTSpice. Figure 12
shows the simulated output of the circuit in figure 11.
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Figure 11: This is a schematic and netlist of a current dependent current source
Figure 12: This is a schematic and netlist of a current dependent current source
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