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Independent and Dependent Sources

There are two principal types of source, namely voltage source   and current source.  Sources can be either independent or dependent upon some other quantities.

An independent voltage source  maintains a voltage (fixed or varying with time) which is not affected by any other quantity. Similarly an independent current source  maintains a current (fixed or time-varying) which is unaffected by any other quantity. The usual symbols are shown in figure 1.3.

 figure215
Figure 1.3: Symbols for independent sources 

Some voltage (current) sources have their voltage (current) values varying with some other variables. They are called dependent   voltage (current) sources or controlled voltage (current) sources , and their usual symbols are shown in figure 1.4.

Remarks -- It is not possible to force an independent voltage source to take up a voltage which is different from its defined value. Likewise, it is not possible to force an independent current source to take up a current which is different from its defined value. Two particular examples are short-circuiting an independent voltage source and open-circuiting an independent current source. Both are not permitted.

 figure292
Figure 1.4: Symbols for dependent sources. Variables in brackets are the controlling variables whose values affect the value of the source.  



Michael Tse
Tue Mar 10 13:15:28 HKT 1998