I-V Characteristics of Zener Diode

1. Welcome

2. Md.Mujahiduzzaman

3. Zener diodes are a special kind of diode
which permits current to flow in the
forward direction. What makes them
different from other diodes is that Zener
diodes will also allow current to flow in
the reverse direction when the voltage is
above a certain value.

4. A Zener diode allows current to flow from its anode to its
cathode like a normal semiconductor diode, but it also permits
current to flow in the reverse direction when its "Zener
voltage" is reached.

5. The term regulator means which
regulates or controls. Zener diode
can work as a voltage regulator if it
is introduced in a circuit. The output
across the diode will be constant. It
is driven by a current source. As we
know if the voltage across the diode
exceeds a certain value it would
draw excessive current from the
supply. The basic diagram of zener
diode as voltage regulator is given
in picture.

7. The phenomenon of zener breakdown is related to the concept of avalanche
breakdown. Zener breakdown is achieved by heavily doped regions in the
neighbourhood of ohmic contact. It is the second method of disturbing the
covalent bonds of the crystal atoms and increasing the reverse bias zener
diode current, to be sustained at a much lower specific voltage than normal
diode. The reverse bias voltage known as zener voltage, where this
mechanism occurs is determined by the diode doping concentration and it
occurs when the depletion layer field width is sufficiently enough to
disrupting the covalent bonds and cause number of free charge carriers due
to electric field generation to swell.

11. Zener Diodes are used in the "REVERSE" bias mode, i.e. the anode
connects to the negative supply, and from its I-V characteristics curve
above, we can see that the Zener diode has a region in its reverse bias
characteristics of almost a constant voltage regardless of the current
flowing through the diode. This voltage across the diode (it's Zener
Voltage, Vz) remains nearly constant even with large changes in
current through the diode caused by variations in the supply voltage
or load. This ability to control itself can be used to great effect to
regulate or stabilise a voltage source against supply or load variations.
The diode will continue to regulate until the diode current falls below
the minimum Iz value in the reverse breakdown region.