Introductory Electronics

Models of Diodes   1.    Why use different models for diode? we have seen how the I-V characteristic of a PN Junction diode reveals exponential dependence of junction current on biasing voltage , given by This implies the necessity to solve exponential equations for obtaining exact values of current and voltages in circuits having diodes, which actually can't be expressed in closed form . So to simplify our life, we adopt standard approximations for behaviour of diode, called models for analysing various circuits.   2.    The IDEAL Diode Model This model assumes that as soon as the diode is forward biased , even if the biasing voltage is just tiny bit greater than 0 volts, the diode acts as a short circuit and can be modelled by a short circuiting wire. On the other hand, as soon as its reverse biased , it starts behaving as an open circuit , even though the biasing voltage is just infinitesimally negative. In essence, all this

Biasing of Diodes   1.    What is biasing?  Having Understood the structure and equilibrium of a PN Junction diode without any external potential difference applied, its time now to see what happens one the application of an external potential difference: We know diodes are Directional  in nature, i.e their polarity matters due to the simple fact that they are  not symmetric  due to opposite charges on either side. So right off the bat we can predict application of potential can be done in two ways-   1. From n side to p side, 2. From p side to n side. Now, when we apply positive potential to P-side of diode, and of course ground / lower voltage to N-side the resulting configuration is called Forward Bias. Similarly when the opposite is done, resulting configuration is called Reverse Bias.     2.    Forward bias explained  As shown, the external electric field due to the battery points from p side to n side . This field opposes  the direction of field in the d

PN Junction Diodes    1.    What are they? For starters, all you need to know for getting started are: Semiconductors like Silicon & Germanium  have 4 valence electrons in their normal state. When either a relatively electron  rich or electron  deficient  elements like Boron(3 valence electrons) or Phosphorus(5 valence electrons) are mixed with pure semiconductors (this mixing is formally called Doping ), we obtain n-type  or p-type  semiconductor. n-type  being the one with higher electron density  due to presence of electron rich element. Similarly p- type being the one with electron deficiency.  The electron deficient spots are considered as a positive charge carrier("assumed") and are called holes . Now when a layer(or wafer) of p-type & n-type semiconductors each are joined together, a strange rearrangement of charges takes place along with development of electric field, this bilayered structure is called a  PN Junction Diode  (a PN junction