Saturday, March 12, 2011

pn junction diode and its v/i characteristics

diode is one of the most common element of is used widely here is the post explaining v/i characteristics of diode

The operation of diodes (as with other semiconductor devices) is often described by a special graph called a "characteristic curve". These graphs show the relationship between the currents and voltages associated with the different terminals of the device. An understanding of these graphs helps in understanding how the device operates.
For diodes the characteristic curve is called an I/V curve because it shows the relationship between the voltage applied between the anode and cathode, and the resulting current flowing through the diode. A typical I/V characteristic is shown in figure:

The axes of the graph show both positive and negative values and so intersect at the centre. The intersection has a value of zero for both current (the Y axis) and voltage (the X axis). The axes +I and +V (top right) show the current rising steeply after an initial zero current area. This is the forward conduction of the diode when the anode is positive and cathode negative. Initially no current flows until the applied voltage is at about the forward junction potential, after which current rises steeply showing that the forward resistance (I/V) of the diode is very low; a small increase in voltage giving a large increase in current.

The -V and -I axes show the reverse biased condition (bottom left). Here we see that although the voltage increases hardly any current flows. This small current is called the leakage current of the diode and is typically only a few micro-amps with germanium diodes and even less in silicon. If a high enough reverse voltage is applied however there is a point (called the reverse breakdown voltage) where the insulation of the depletion layer breaks down and a very high current suddenly flows. In most diodes this breakdown is permanent and a diode subjected to this high reverse voltage will be destroyed. In Zener diodes however, this point is used to give the diode its special ability to stabilise the applied voltage: If the voltage increases at this point heavy current flows and reduces the voltage. The breakdown in a Zener diode is not destructive due to its special construction.

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Himanshu Dureja is an engineering student and part time blogger.