Sources
Sources
are of two types:
-
Voltage
source
-
Current
source
Similarly,
sources can also be categorized as:
-
Independent
source
-
Dependent
source
Definition:
An ideal independent source is an
active element that provides a specified voltage or current which is completely
independent of other current elements
An
ideal dependent (or controlled) source
is an active element in which the source quantity is controlled by another voltage
or current.
There
are four types of dependent sources:
-
Voltage
controlled voltage source;
-
Current
controlled voltage source;
-
Voltage
controlled current source;
-
Current
controlled current source.
Dependent
sources are used in modeling elements such as transistors, op-amps etc.
Example
of dependent source in a circuit:
-
The
value of dependent source is 10i Volts
(it’s a voltage source NOT current source).
-
Voltage
source comes with polarity (+ -), while current source comes with arrow.
-
Any
voltage some (depended or independent) can supply any current to ensure its
terminal voltages remains as stated (rated). Therefore, for voltage source, we
know the voltage but not current unless analyzed.
-
Similarly,
any current (depended or independent) source can supply necessary voltage to
ensure stated current flow. Therefore, for current source, we know the current
but voltage unless analyzed.
-
An
ideal source can therefore produce infinite amount of energy.
-
Sources
can supply as well as absorb power.
Ex:
Calculate the power supplied or absorbed by each element of the circuit below:
|
p = +vi (power absorbed)
p=-vi (power supplied)
p1 = -20 x 5 = -100W
p2 = 12 x 5 = 60W
p3 = 8 x 6 = 48W
p4 = -8 x 0.2(5) = -8W
|
p1 and p4 are supplying power;
p1 + p2
+ p3 + p4 = -100 + 60 + 48 -8 = 0W
Total
power supplied is equal to total power absorbed.
|
Ex:
Calculate the power supplied or absorbed by each element of the circuit below:
p1= -5 x 8= -40W
p2= 2 x 8= 16W
p4=3 x 5 = 15W
p3 = 0.6(5) x 3 = 9W
p1 + p2 + p3 + p4 = -40+16+15+9 = 0
