A current source, unlike the DC voltage source, is not a physical reality. How ever, it i s useful in deriving equivalent circuit models of semiconductor devices such as a transistor. It can also be subdivided into ideal and non-ideal categories.
The Ideal Current Source By deﬁnition, an ideal current source, that produces a current which is independent of the variations in load. In other words the current supplied by an ideal current source does not change with the load voltage.
Non-Ideal or Practical Current Source The current delivered by a practical current source falls off with an increase in load or load voltage.