ZENER DIODE AS VOLTAGE REGULATOR PDF
Electronics Tutorial about the Zener Diode and how the Zener Diode can be used with a series resistor to produce a Zener Diode Voltage Regulator Circuit. 1. Zener diodes as voltage regulators. A Circuit diagram symbol for a zener diode . Zener diodes are used in circuits to maintain a fixed voltage across a load. The Zener diode specially made to have a reverse voltage breakdown at a specific voltage.
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diodes. In breakdown the voltage across the Zener diode is close to range of currents thus making it useful as a shunt voltage regulator. Zener Voltage Regulators This series of Zener diodes is packaged in a SOD− FL surface Standard Zener Breakdown Voltage Range − V to 75 V . coverage may be accessed at olhon.info−olhon.info A series of experiments were carried out to investigate the operation and performance of zener diode voltage regulators. Measurements were taken and.
The unvarying reverse voltage of a zener diode renders it as a very useful component in controlling the output voltage against the variations in load resistance or variations in the input voltage provided from an unstable voltage source such as the battery bank of a renewable energy system which will fluctuate depending on the state of charge of the bank.
The current through the Zener diode will change to keep the voltage within the adjustable threshold limits of zener action. Manufacturers rate zener diodes according to their Vz value and the maximum power dissipation at room temperature i.
This is an indication of the maximum reverse current that a zener diode can safely conduct electric current. Each zener knee voltage value is generally specified at lowest zener current. As a result the power dissipation values are used to indicate the safe operating range.
Typical values of power dissipation ratings are from mW to 50W. Zener diode can be identified by the terminal that is by observing a black color ring at cathode terminal. If the diode is an SMD component, then a colour band will be available for cathode terminal. By recognizing the zener diode code marked over the device, we can determine the value of it.
BACK TO TOP Zener Diode I-V Characteristics Curve In the forward bias condition, the zener diode behaves like an ideal diode within specified current and power limits, but it differs in reverse bias condition where the zener diode has very steep avalanche characteristic at the breakdown voltage in reverse bias condition. Zener operates mainly in the reverse bias mode by connecting anode to the negative terminal of the power supply.
Zener diodes are categorised and rated by the voltage at which they will turn on or start to conduct the reverse bias current. Generally these zener diodes are used to regulate the voltage.
In reverse bias condition after the break down zener diode provides a constant output voltage even if we increase the input voltage. This mechanism is also referred to as impact ionisation or avalanche multiplication. For reverse conduction it is necessary to visualise the phenomenon of avalanche breakdown. This process begins when a large negative bias is applied to the PN junction, sufficient energy is imparted to thermally generated minority charge carriers in the semiconductors.
As a result the free carriers acquire required kinetic energy to break the covalent bonds and create an electric field through collisions with crystal particles.
The charge carriers created in collision contribute to the reverse current, well beyond the normal reverse saturation current and may also possess enough energy to participate through collisions, creating an additional electric field and the avalanche effect by impact ionization, once a sufficiently high reverse bias is provided this process of conduction takes place very much like an avalanche: a single electron can ionise several others.
This mechanism is also referred to as a high field emission mechanism. 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.
The true Zener effect in semiconductors can be explained in terms of two upper energy bands are of interest. The two upper energy bands are namely the conduction band and the valence band. Either of these effects or a combination of the two mechanisms significantly increases the current in the reverse bias region while having a negligible effect in the voltage drop across the junction.
When the applied reverse bias voltage is greater than a predetermined voltage, zener breakdown takes place. The zener breakdown voltage is made sharp and distinct by controlling the doping concentration and when surface imperfections are avoided. The voltage across the zener diode in breakdown region is almost constant that turns out to be an essential concept in regulating the voltage. A voltage stabilizer is a combination of elements that are designed to ensure the output voltage of a supply fairly remains constant.
Excess voltage protection is done by using zener diodes because there will be reverse current due to minority charge carriers starts flowing through the diode after the reverse bias voltage exceeds a certain value. Keeping the zener diode in parallel with a variable load resistance RL, ensures a constant output voltage even though the load current and the supply voltage varies.
In practical circuits the simplest form of current source is a resistor.
This type of arrangement of the circuit provides safety for equipment connected to terminals. This arrangement of regulator circuit is referred to as a shunt regulator in which the regulating element is placed in parallel with the load. The input voltage to the system is a few volts and as long as it is more than the desired output voltage, a stable voltage will be produced across the zener diode.
Usually the reverse current should not exceed normal value but, if due to any fault in circuit construction the current exceeds maximum allowable limit, the system will damage permanently. However to avoid unbalanced performance, zener diodes are used for voltage reference in many measuring instruments.
As the input voltage increases, current through the zener diode increases, but the drop in voltage remains constant which is the necessary feature required for zener diodes. Therefore, reverse current in the circuit has increased, voltage drop across the resistor increases by an amount equal to the difference between the applied input voltage and the zener knee voltage of the zener diode. The output voltage of regulator system is fixed as the zener knee voltage of the zener diode and can be used in power devices requiring a fixed voltage of firm value.
Plot the graphs for line and load regulation and find the values by taking the slopes of the graphs. Now keep the input voltage constant and vary the rheostat at output.
Now take the voltmeter and ammeter readings by varying the input voltage 6. Note down the voltmeter and ammeter readings 6. Calculating voltage and current The total current drawn from the source is the same as that through the series resistor The current through the load resistor is and the zener diode current is If the voltage source is greater than Vz and If the voltage source is less than Vz and.
Output voltage remains the same as long as the input voltage is maintained above a minimum value. Output volt remains same. Using a resistor to ensure that the current passing through the Zener diode is at least 5mA 0. Line regulation and load regulation was calculated. Graphs were plotted. Since the voltage dropped across a Zener Diode is a known and fixed value.
Zener diodes are typically used to regulate the voltage in electric circuits.
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The Zener Diode Voltage Regulator
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Zener Diode Tutorial
Alejandro Fulgen. More From Huri Mughal. Huri Mughal. Popular in Electric Power. Tushar Goyal.They categorized by power dissipation, nominal working voltage, forward current, forward voltage, packaging type and maximum reverse current. Limiting Circuits With no Load Lesson 4. From the table, we see that results are the points that lie on the plot of the first quarter of I-V curve, as illustrate in Figure 6 below.
Project Title: The power dissipated in the resistor is equal to the voltage drop across the resistor multiplied by Imax. This filtered DC voltage is regulated by the diode to provide a constant reference voltage of 15V.
Here is a simple question for the readers — Why are regulator ICs mostly preferred over Zener diode in regulated DC power supply? For Wave Shaping Zener diodes are also used to convert sine wave into square waves.
And the electron hole pair generation takes place.