Ordinary diode allows current to flow in one direction
only, zener diode on the other hand allows the current to flow on both
direction. When the zener is forward bias, the voltage drop across is
around 0.7V, which is equal to the ordinary diode. But if the zener is reverse
bias, it has a voltage drop equal to its breakdown voltage, where
in this case, ordinary diode is open circuit or not conducting.
One of the uses of this
diode is for voltage regulation or voltage reference.
The figure below is an example on how the zener diode provides regulation
across the load. the voltage output is equal to the zener diode
voltage.
Example:
V_input = 15V
Zener = 10V
R = 500 ohm
Load = 2000 ohm
we can say that the
current delivered to the load is equal to Vload/Iload
where Vload = Vzener = 10V, thus current of load = 5mA
where Vload = Vzener = 10V, thus current of load = 5mA
Zener can be connected
in series to each other or connected back to back depending on its
purpose. Series connection (see circuit below), provides
different voltage reference or output with one input only.
Example the input voltage is 35V, you can have an output of 25V and
10V connecting 25v and 10V zener in series.
Zener diode also can be
connected back to back to provide voltage regulation especially in
square wave or sine wave signal input. Example a sinusoidal wave has a
magnitude of 50V at 60Hz (see circuit below), the two zener diodes connected
back to back provides a regulated output of with the maximum magnitude of
output equal to +15V and -15V.See the output voltage (faded blue) and
input voltage in diagram below.
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