Superposition

Superposition is a good method to apply in analyzing circuits with multiple sources. The basic concept of this method is to analyze a circuit one source at a time. Using the Superposition Theorem, we remove all the independent sources, except one, and analyze that circuit for that one. Then we repeat the procedure for another source, and so on. Finally, the net result is found by summing all the single -source results. 

'Removing' Power Sources

If we have two voltage sources and we were to remove one source, and still have a complete circuit, we must replace the voltage source with a short circuit.

Source Transformation

In order to solve difficult and complicated circuits, it is important to simplify the given circuit for easier analysis. One way to simplify circuits is by Source Transformation. It is the process of using Ohm's Law to take an existing voltage source in series with a resistance, and replace it with a current source in parallel with the same resistance or vice-versa. This method can be applied to Thevenin's theorem and Norton's theorem.

Source Transformation for Independent Sources

Bipolar Junction Transistor

The bipolar junction transistor (BJT) is a three-element (emitter, base, and collector) device made up of alternating layers of n- and p-type semiconductor materials joined metallurgically. The transistor can be of pnp type (principal conduction by positive holes) or of npn type (principal conduction by negative electrons), as shown in Fig. 3-1 (where schematic symbols and positive current directions are also shown). The double subscript notation is utilized in labeling terminal voltages, so that, for example, Vbe symbolizes the increase in potential from emitter terminal E to base terminal B. For reasons that will become apparent, terminal currents and voltages commonly consist of superimposed dc and ac components (usually sinusoidal signals).

Wye-Delta Conversion

In many circuits, resistors are neither in series nor in parallel, so the rules for series or parallel circuits described in previous chapters cannot be applied. For these circuits, it may be necessary to convert from one circuit form to another to simplify the solution. Two typical circuit configurations that often have these difficulties are the wye (Y) and delta (D) circuits.

Wye to Delta