Zener Diode is basically the same as the standard PN connection diode, but is specially designed to have a low and specified Reverse Fault Voltage that takes advantage of any reverse voltage applied.
A semiconductor diode blocks the current in the opposite direction, but is subjected to premature distortion or damage if the applied reverse voltage rises too high.
Zener diode acts as general use diodes if it is polarized forward, that is, used as it should be used. However, unlike a traditional diode that blocks any flow of current from within itself when inverted, that is, if the Cathode becomes more positive than the Anode, as soon as the reverse voltage reaches a predetermined value, the zener diode begins to transmit in the circuit.
This is because when the reverse voltage applied to the zener diode exceeds the nominal voltage of the diode, an event called AvalancheBreakdownoccurs in the semiconductor exhaustion layer and a current begins to flow through the diode to limit this increase in voltage.
Now the current flowing from the zener diode increases significantly to the maximum circuit value (usually limited to a series of resistance), and once achieved, this reverse saturation current remains quite constant in a wide range of reverse voltages.The voltage point on the Zener diode is called "zener voltage" (Vz), and for zener diodes, this voltage can vary from one volt to several hundred volts.
The point at which zener voltage triggers the current passing through the diode gives the diota a certain zener refractive voltage (Vz) that can be controlled very precisely (up to less than 1% tolerance) during the doping phase of the diode semiconductor structure. for example, 4.3V or 7.5V.This zener fault voltage on the IV curve is almost a vertical straight line.
This voltage remains almost constant even with major changes in the current, provided that the zener diode current remains between the fault current/refractive current IZ(min) and the maximum current rating IZ(max).
This ability of the Zener diode to control itself can be used to regulate or stabilize a voltage source against feeding or load changes.It turns out that zener diode is an important feature because the voltage passing through the diode in the fault zone is almost constant and can be used in the simplest type of voltage regulator applications.
The function of a voltage regulator is to provide a constant output voltage to a load connected to it in parallel, despite fluctuations in the feed voltage or changes in the load current.A zener diode will continue to regulate its voltage until the diodes holding the current fall below the minimum I Z(min) in the reverse fault zone.
Zener Diode Regulator
Zener Diode can be used to produce a stabilized voltage output with low fluctuation in changing load current conditions.The circuit can be completed in a healthy way using a suitable current limiting resistance.
We remember from previous tutorials that the DC output voltage from the half or full wave rectifiers contains fluctuations superimposed on the DC voltage and changes the average output voltage as the load value changes.By connecting a simple zener stabilizer circuit to the output of the rectifier, as shown below, we can produce a more stable output voltage.
Resistance is serially connected with zener diode to limit current flow through the diode with the RS voltage source.
Zener diode is connected by the cathode terminal, which is connected to the positive rail of the DC welding, so it will work in case of reverse polarity and failure.
When the load is not connected to the circuit, the load current will be zero ( I L = 0 ) and the entire circuit current will pass through the zener diode, which will distribute the maximum power of the circuit.In addition, the fact that RS resistance has a small value will result in a larger diode current when the load resistance is connected to RL, and since this will increase the need for the diode to expend power, caution should be taken when choosing the appropriate resistance value. Under this loadless or high impedance condition, the maximum power rating of zener should not be exceeded.
The load is connected in parallel with the zener diode, so the voltage on the R L is always the same as the zener voltage, ( V R = V Z ).There is a minimum zener current in which the stabilization of the voltage is effective, and the zener current should always remain above this value when working under load in the fault zone.The upper limit of the current, of course, depends on the degree of power of the device.The supply voltage must be greater than V S, V Z.
When using Zener diode with stabilizer circuits, there is a small problem. It is the ability of the diode to produce electrical noise on the DC source when trying to balance the voltage.Normally this is not a problem for most applications, but it may be necessary to add a large value decauplage capacitor to the zener output to provide additional softening.
A zener diode is always operated in case of reverse polarity.Such a simple voltage regulator circuit provides a constant DC output voltage throughout the load, despite changes in input voltage or changes in load current.
The Zener voltage regulator consists of a zener diode that is connected parallel to the R L load in this reverse-sided state, and the input voltage consists of R S from a current limiting resistance serially connected with V S.The stabilized output voltage is always selected so that the distortion voltage of the diode is the same as the V Z.
Zener Diode Question Example 1
A 5.0V stabilized power supply is required to be produced from a 12V DC power supply input source. The maximum power rating PZ of the zener diode is 2W. Using the zener regulator circuit above calculate:
5V will be regulated and used from the 12V DC power supply.The maximum power rating of the Zener diode is PZ = 2W. Using the above zener regulator circuit, calculate the:
1. Maximum current passing through zener diode:
2. Minimum value of RS resistance:
3. If a load resistance of 1kΩ is connected to the Zener diode, what is the load current IL?
4. What is the zener current IZ at full load?
Zener Voltage Diodes
In addition to producing a single stabilized voltage output, zener diodes can also be connected in series with normal silicon signal diodes to produce various different reference voltage output values, as shown below.
Serial Connected Zener Diodes
While the values of individual zener diodes can be selected to fit the application, silicon diode always drops by approximately 0.6 – 0.7V in the case of forward polarity.The feed voltage, Vin, of course, should be higher than the largest output reference voltage, and in our example above this is 19v.
A typical zener diode for general electronic circuits is the 500mW, BZX55 series or larger 1.3W, BZX85 series, for example, the zener voltage is given as C7V5 for 7.5V diode and the diode reference number is given as BZX55C7V5.
The 500mW series of zener diodes are available from approximately 2.4 to about 100 volts and typically have the same range of values as those used for the 5% (E24) resistance series with separate voltage ratings for these small but very useful diodes.
So far, we have examined how to use a zener diode to regulate a fixed DC source, but what to do either when the input signal is the AC waveform instead of dc, we will examine in our article "Diode Clipping Circuits".