Ideal voltage & current sources

  • An ideal voltage source is a circuit element that maintains a prescribed voltage across its terminals no matter how the current flows through it.
  • An ideal voltage source has zero internal resistance. Therefore it cannot be shorted.
  • The current in an ideal voltage source can be zero if no loads are connected to the source.

There’s two types of voltage sources:

  1. independent, like (a)
  2. and dependent (or sometimes called controlled) voltage sources, like (b) and (c)
  • An ideal current source is a circuit element with a prescribed current flowing through its terminals no matter what the voltage across the terminals is.
  • In theory, an ideal current source has infinite internal resistance.
  • The arrow in the circle shows the reference direction of the current in the source.

There are two types of current sources.

  1. Independent current sources, like (a)
  2. and dependent current sources, or controlled current sources, like (b) and (c).
    • (b) is a voltage controlled current source, or VCCS.
    • (c) is a current controlled current source, or CCCS.

Example #1 (fake circuit)





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