WEBVTT

00:00.000 --> 00:05.760
Now, we will discuss voltage and current sources

00:05.760 --> 00:11.159
An electrical source is a device which converts
mechanical, thermal, chemical or some other

00:11.159 --> 00:24.159
form of energy into electrical energy. There are two
types of sources, voltage sources and current sources

00:24.159 --> 00:37.959
Voltage sources are further categorized as ideal
voltage source and practical voltage source

00:37.959 --> 00:51.119
Examples of voltage sources are batteries, dynamos, alternators, etc. Ideal
voltage source is defined as the energy source which gives constant voltage across

00:51.119 --> 01:05.680
its terminals irrespective of current drawn through its
terminals. The symbol of ideal voltage source is shown here

01:05.680 --> 01:19.440
In an ideal voltage source, the terminal voltage
is independent of the load impedance, RL connected

01:19.440 --> 01:24.519
Whatever is the voltage of the source, the
same voltage is available across the load

01:24.519 --> 01:32.919
terminals of RL i.e. VL equals VS
under loading condition as shown here

01:32.919 --> 01:37.839
There is no drop of voltage in the
source supplying current to the load

01:37.839 --> 01:47.160
The internal resistance of the source is therefore zero. In a practical
voltage source, there will be a drop in voltage available across the

01:47.160 --> 01:53.559
load due to voltage drop in the resistance of
the source itself when a load is connected

01:53.559 --> 02:00.639
as shown here. In certain applications, a constant
current flow through the circuit is required

02:00.639 --> 02:06.559
When the load resistance is connected between
the output terminals, a constant current iL

02:06.559 --> 02:19.720
will flow through the load. The examples of current sources
are photoelectric cells, collector current in transistors, etc

02:19.720 --> 02:32.039
The symbol of current source is shown here

02:32.039 --> 02:42.919
Now we will come to practical
voltage and current sources

02:42.919 --> 02:49.279
A practical voltage source like a battery
has the drooping load characteristics due

02:49.279 --> 03:01.880
to some internal resistance. A voltage source
has small internal resistance in series

03:01.880 --> 03:16.360
On the other hand, a current source has
some high internal resistance in parallel

03:16.360 --> 03:31.399
For ideal voltage source, internal series resistance is zero. For
ideal current source, parallel internal resistance is infinity

03:31.399 --> 03:39.320
A practical voltage source is shown as an ideal
voltage source in series with a resistance

03:39.320 --> 03:45.839
This resistance is called the internal
resistance of the source as shown here

03:45.839 --> 03:51.479
A practical current source is shown as an
ideal current source in parallel with its

03:51.479 --> 04:16.839
internal resistance as shown here. From this figure, we can
write VL at open circuit condition is equal to VS i.e. when

04:16.839 --> 04:23.679
the load is removed, the circuit becomes an
open circuit and the voltage across the source

04:23.679 --> 04:40.079
becomes the same as the voltage across the load terminals. When the load
is short circuited, the short circuit current IL will be VS by RSE where

04:40.079 --> 05:09.920
RSE is the internal resistance of the source. In the same way, from
this figure, we can write VL at open circuit equals to ISH into RSH

05:09.920 --> 05:30.040
And IL at short circuit equals to IS

05:30.040 --> 05:32.519
Hope you got the idea. Thank you