1. There are several voltage sources as well as current sources encountered in our daily life. Batteries, DC Generator or alternator all are very common examples of voltage source. There are also some current sources encountered in our everyday life, such as photo electric cells, semiconductor devices like transistors etc.

2. The sources can be categorized into two different types –
Independent source
Dependent source.

3. Independent Voltage Source
Output of an independent source does not depend upon the voltage or current of any other part of the network. When terminal  voltage  of a voltage source is not affected by the  current or  voltage  of any other part of the network, then the source is said to be an independent Voltage Source
 This type of sources may be referred as constant source or time variant source. When terminal  voltage of an independent source remains constant throughout its operation, it is referred as time–invariant or constant independent  Voltage Source

4. Again independent Voltage Source can be time–variant type, where the output terminal voltage  of the source changes with time. Here, the terminal  voltage  of the source does not vary with change of  voltage  or  current of any other part of the network but it varies with time.

5. Independent Current Source
Similarly, output  current  of independent  current source  does not depend upon the voltage or  current  of any other part of the network. It is also categorized as independent time-invariant and time-variant  current source.

7. Independent Source
Those sources which do not depend upon the values of the current or the voltages in any other part of that circuit are called independent sources.
An independent voltage source is a Thevenin Equivalent of power source as shown below:

8. Independent Source Cont’d
An independent current source is Norton Equivalent of power source as shown below.

9. Ideal Source
An ideal voltage source is that source which : a) Has Zero internal impedance. b) Gives a constant terminal voltage irrespective of the load current. An ideal current source is that source which: a) Has Infinite internal impedance. b) Gives constant terminal current irrespective of the load voltage.

10. Dependent Sources

11. Dependent Sources 
A Dependent Source is similar to an independent source except its value depends on some other voltage or current elsewhere in the circuit.  A dependent source represents a device that amplifies or responds to another signal elsewhere in the circuit.

12. Four types of Dependent Sources:
Voltage Controlled Voltage Source (VCVS) - This is a voltage source that depends on some voltage.
Current Controlled Voltage Source (CCVS) - This is a voltage source that depends on some current.
Voltage Controlled Current Source (VCCS) - This is a current source that depends on some voltage.
Current Controlled Current Source (CCCS) - This is a current source that depends on some current.

13. VCVS
This is a dependent voltage source. The voltage across the source depends on Vx. For example, if Vx=5V and u=3 then the voltage across the source is uVx or 15V. The value of u is unitless and is determined by how the dependent source is designed.

14. CCVS:
This too is a dependent voltage source. The voltage across the  source depends on the current Ix. For example, if Ix=2A and u=10 then the voltage across the source is uIx or 20V. The value of u is determined by how the dependent source is designed. Since the dependent source puts out voltage, its value is always expressed in volts, even though the source depends on a current. u converts from Amps to Volts.

15. VCCS
This is a dependent current source. The current through the source depends on the voltage Vx. For example, if Vx=10V and g=0.5 then the current through the source is gIx or 5A. The value of g is determined by how the dependent source is designed. Since the dependent source puts out current, its value is always expressed in amps, even though the source depends on a voltage. g converts from Volts to Amps.

16. CCCS
This is a dependent current source. The current through the source depends on Ix. For example, if Ix=3A and B=2 then the current through the source is BIx or 6A. The value of B is unitless and is determined by how the dependent source is designed.

17. Types of controlled Source

18. Source Conversions Circuit analysis
Sometimes convenient to convert between voltage sources and current sources
To convert from a voltage source to a current source
Calculate current from E/RS

19. Source Conversions RS does not change
Place current source and resistor in parallel

20. Source Conversions
Can also convert from a current source to a voltage source
E = I•RS
Place voltage source in series with resistor

21. Source Conversions

22. Source Conversions
A load connected to a voltage source or its equivalent current
Should have same voltage and current for either source

23. Source Conversions Although sources are equivalent
Currents and voltages within sources may differ
Sources are only equivalent external to terminals

24. Current Sources in Parallel and Series
Simply add together algebraically
Magnitude and direction of resultant source
Add currents in one direction
Subtract currents in opposite direction

25. Current Sources in Parallel and Series
Current sources with different values
Never place in series
This violates KCL