How Usefulness the concept of voltage and current source in Electronics
As we proceed with the study of electronics, we find that the concept of voltage and current sources are of great help. For example, in determining the performance of an electronic circuit (such as amplifier, which is used to amplifying electrical signals).
We convert the original circuit into its equivalent AC circuit. In this equivalent circuit, the active device (such as a BJT or an FET) is replaced by its current-source equivalent or voltage-source equivalent.
We can now apply the basics of circuit theory to determine the characteristic behavior of the electronics circuit.
The following figure shows the V-I Characteristics and symbol of a semiconductor device called the zener diode.
If we compare its characteristics with that of a DC voltage source, we will find similarity. The only difference is that the characteristics curve of the zener diode is inverted.
It is shown inverted to emphasize that the zener diode is operated with reverse bias.
This means that the current through the zener diode flows in a direction opposite to that of the arrow (in its symbol).
Let us see what happens if we connect a zener diode across a practical voltage source as shown in the following figure:
If the load impedance RL varies, the current IL through it also varies. If the zener diode were not there, the terminal voltage VT would also vary, because the voltage drop across the source impedance varies. But now, since zener diode is connected across terminals A and B, and it has characteristics quite similar to that of an ideal voltage source, the situation is different. The terminal voltage VT remains constant at VZ whatever be the current flowing through the zener diode.
When the load current varies, the zener diode current adjusts itself so that its terminal voltage remains constant. This is an example of simple voltage regulator circuit.
It ensures safe operation of the zener diode.
In the above figure a zener diode when connected in the circuit it works as a voltage source. Strictly speaking, it is not a source, because it can not supply any power its own.
We need another voltage source for its operation. Once it is connected in an electrical circuit, it has V-I characteristics similar to that of a constant voltage source.
Loosely speaking, we can say that a zener diode is a constant dc-voltage source.
0 Comments
Please Don't post spam comments