Diodes are used to convert AC into DC
these are used as half wave rectifier or full wave rectifier. Three points must
he kept in mind while using any type of diode.
1.Maximum forward current capacity
2.Maximum reverse voltage capacity
3.Maximum forward voltage capacity
The number and voltage capacity of some of the important diodes available in the market are as follows:
· Diodes of number IN4001, IN4002, IN4003,
IN4004, IN4005, IN4006 and IN4007 have maximum reverse bias voltage capacity of
50V and maximum forward current capacity of 1 Amp.
· Diode of same capacities can be used in place
of one another. Besides this diode of more capacity can be used in place of
diode of low capacity but diode of low capacity cannot be used in place of
diode of high capacity. For example, in place of IN4002; IN4001 or IN4007 can
be used but IN4001 or IN4002 cannot be used in place of IN4007.The diode
BY125made by company BEL is equivalent of diode from IN4001 to IN4003. BY 126
is equivalent to diodes IN4004 to 4006 and BY 127 is equivalent to diode
IN4007.
PN JUNCTION OPERATION
Now that you are familiar with
P- and N-type materials, how these materials are joined together to form a diode, and the function of the diode, let
us continue our discussion with the operation of the PN junction. But before we can understand how the PN junction works, we
must first consider current flow in the materials that
make up the junction and what happens initially within the junction when these
two materials are joined together.
Current Flow in the N-Type Material
Conduction in the N-type
semiconductor, or crystal, is similar to conduction in a copper wire. That is, with voltage applied across the material, electrons
will move through the crystal just as current would flow
in a copper wire. This is shown in figure 1-15. The positive potential of the
battery will attract the free electrons in the
crystal. These electrons will leave the crystal and flow into the positive
terminal of the battery. As an electron leaves the
crystal, an electron from the negative terminal of the battery will enter the crystal, thus completing the current
path. Therefore, the majority current carriers in the N-type material (electrons) are repelled by the negative side of the
battery and move through the crystal toward the
positive side of the battery.
Current Flow in the P-Type Material
Current flow through the
P-type material is illustrated. Conduction in the P material is by positive holes, instead of negative
electrons. A hole moves from the positive terminal of the P material to the negative terminal. Electrons from the external circuit enter
the negative terminal of the material and fill holes
in the vicinity of this terminal. At the positive terminal, electrons are
removed from the covalent bonds, thus creating new
holes. This process continues as the steady stream of holes (hole current)
moves toward the negative terminal