Independent and Dependent Electrical Sources

Two types of elements in electric circuits:
1. passive elements
2. active elements
An active element is capable of generating energy while a passive element is not.
Passive elements : resistors, capacitors, and inductors.
Active elements : generators, batteries, and operational amplifiers
Our aim in this section is to gain familiarity with some important active elements.
The most important active elements are voltage or current sources that generally deliver power to the circuit connected to them.
There are two kinds of sources: independent and dependent sources.

Sources: Voltage and Current
A Voltage Source is a device that generates an exact output voltage which, in theory, does not change regardless of the load current
A Current Source is capable of supplying a constant current flow to a circuit regardless of the voltage developed across its terminals
Sources can be Ideal or Practical

An ideal independent source is an active element that provides a specified voltage or current that is completely independent of other circuit elements.

An ideal independent voltage source delivers to the circuit whatever current is necessary to maintain its terminal voltage.
Physical sources such as batteries and generators may be regarded as approximations to ideal voltage sources.
An ideal independent current source is an active element that provides a specified current completely independent of the voltage across the source.
That is, it delivers to the circuit whatever voltage is necessary to maintain the designated current.

An ideal dependent (or controlled) source is an active element in which the source quantity is controlled by another voltage or current.
diamond-shaped symbols.

Control of the dependent source is achieved by a voltage or current of some other element in the circuit, and the source can be voltage or current
Four possible types of dependent sources:
1. A voltage-controlled voltage source (VCVS)
2. A current-controlled voltage source (CCVS)
3. A voltage-controlled current source (VCCS)
4. A current-controlled current source (CCCS)
Dependent sources are useful in modeling elements such as transistors, operational amplifiers, and integrated circuits.