Download Zener diodes are designed to have a specific reverse voltage

Zener Diodes Primer : How to use Zeners
NomadTronics /Aus.
Zener diodes are designed to have a specific reverse voltage breakdown .
It means that they can function like a switch, or to regulate the voltage by creating a stable voltage
limiting function below the level of a fluctuating input voltage.
In electronic circuits Zener diodes are used as
voltage limiters – to protect other sensitive
components from over-voltage exposure ;
or anywhere where there is a need for a stable
voltage (or reference voltage) and/or a stable
current…
The Zener diode needs a current limiting resitor
(Rs) to maintain its voltage regulating point .
The zener current is constant regardless of load .
Voltage clamps : Limiting signals with Zener
diodes
A varying analog signal can be constrained to a fairly
narrow range of voltages with a single Zener diode. If
you have a voltage that swings between + 7 V and – 7
V, you could use a single 4 V Zener, connected to
ground, to ensure that the signal does not exceed 4 V
or go below -0.7 V (where the diode conducts forward
to ground).
If you wanted to constrain the signal to never go
negative– e.g., for input to an analog-to-digital
converter that accepts signals in the 0 – 5 V range, you
could connect the anode of the Zener diode to a power
rail at 1 V, instead of ground. Then, the output signal
range would be constrained to the range of 0.3 V – 5 V.
Another neat trick is to use two Zener diodes, oppositely
oriented, in series. This can provide a symmetric limit
on the excursion of a signal from ground, for example.
This is also a common configuration for using Zener
diodes as transient supressors.
ADDING AN ORDINARY DIODE
An ordinary diode can also be added to the zener line to increase
the reference voltage.
An ordinary diode develops 0.7v across it when in the "forwardvoltage" mode.
The voltage across the LOAD will be 5.6v + 1.7v + 0.7v = 8v.
This is a very convenient way to create almost any zener reference
voltage.
Combining Zeners in Series or Parallel
Zener diodes can be connected in series to create a higher denomination composite Zener :
for example two 15v Zeners connected in series will have the total of 30v voltage limiting function.
Also they can be stacked in parallel to increase their maximum Current capability and Wattage :
eg: 10pcs of the 4.7v 0.5Watt Zeners connected in parallel will make a 4.7v composite zener capable of
handling up to 5 Watt in total.
Therefore having a limited arsenal of Zener diodes should be sufficient for most types of repair and
design work, without having a full range of all possible denominations..
* Also please check our Adjustable Zener 3-pin device TL431A. This can be used like a Zener diode
with adjustable voltage limiting from 2.5v to 36v
___________________________
Application example:
One method of obtaining a split supply from a non
center tapped transformer, using zeners .
This method may be a convenient solution in some
applications but bare in mind that this will be suitable for
relatively Low-Current circuits only.
Application example:
Zeners can be used to raise the level of a voltage
regulator and obtain a different
regulated voltage output .
Application example:
When a high wattage zener
is not available or for economy
a small zener can be use with a high power transistor to handle
the high current as shown .
A LED is a type of ZENER
Another component that acts exactly like a zener diode is a LED. For example A Red LED can be
considered a 1.7v zener diode and it produces light according to the current flowing through it. It's a
zener diode with a window, - that is optimized for light emission… so you can actually see the current
flowing.
In a typical circuit an LED is connected to a power source via a resistor (in series) which helps to buffer
/stabilize the current flowing through that LED
In LED assemblies this resistor is called a Current-Limiting-Resistor
When the voltage across the LED is below 1.7v, no current flows through the LED.
As soon as the supply voltage reaches 1.7v, the LED starts to illuminate.
As the supply voltage increases, the voltage across the LED remains the same (1.7v) and the "left-over"
voltage appears across the resistor. As the voltage rises across the resistor, more current will flow
through the resistor and this current also flows through the LED and makes it glow brighter.
In the case with a typical Red LED - the voltage across the Resistor will always be 1.7v lower than the
supply voltage.
Other color LEDs will have different voltages due to the different types of semiconductor materials used
in their construction, eg: Orange & Green ~ 2.1v ; Blue & White ~ 3.6v .. these are the typical
numbers - to be used as a “rule of thumb” as there are many variations In the industry
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