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 "forward-voltage" 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 thevoltage 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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