Zener diodes as voltage regulators a circuit diagram symbol for a zener diode. Zener diode is defined as the heavily doped semiconductor which works in the breakdown region. Zener diode as voltage regulator tutorial electronicstutorials. Zener diode working with circuit diagram and applications. A zener diode is very useful when you have a load that needs a. So a low power rated zener diode can regulate the base voltage of the bjt that can pass a huge current through it. This circuit is not too different from how linear regulators work. May 10, 2016 career point cares zener diodes are a special kind of diode which permits current to flow in the forward direction. Recall, from the discussion of the diode characteristics curve,that when a diode reaches reverse breakdown, its voltage remains almost constant even through the current changes drastically, and this is the key to zener diode operation. Note that in a transistor the current required by the base is only 1hfe times the emitter to collector current. A zener diode regulates the voltage drop across a load resistor at 4. Zener diode as a voltage regulator zener diode is a silicon semiconductor with a pn junction that is specifically designed to work in the reverse biased condition. The critical parameter of this type of diodes is the zener breakdown voltage.
The key to the design of this voltage regulator is to choose the resistor r. The process of keeping constant voltage across load regardless of variation of input voltage or load current is called regulation. Building a voltage regulator with an ideal zener diode, construction of a voltage regulator is easy, simply connect the diode between. Pdf performance of shunt voltage regulators based on zener. They are more heavily doped than ordinary diodes, due to which they have narrow depletion region. A series resistancer is placed between a higher voltage v in and it is used to limit the current to the load and zener diode. The zener diode is used to regulate the base voltage which leads to regulated emitter voltage. This is arguably the most common application of zener diodes. When biased in the forward direction it behaves just like a normal signal diode, but when a reverse voltage is.
The circuit consists of an npn transistor and a zener diode along with a series resistor rseries that is connected in series with the input supply. When forward biased, it behaves like a normal signal diode, but when the reverse voltage is applied to it, the voltage remains constant for a wide range of currents. If the input voltage increases, the current through the voltage divider increases and any increase in voltage happens across the other resistor. The zener diode compensates for the variation in load current. The symbol of zener diode is shown in the figure below.
Zener diode is a general purpose diode, which behaves like a normal diode when forward biased. Im having trouble understanding the simple voltage regulator that can be built using a zener diode from section 2. Zener diodes can be used to produce a stabilised voltage output with low ripple under varying load current conditions. The diodes used as voltage regulators are called zener diodes.
Join the electric academy and receive a free pdf of online resources for electricians. In breakdown the voltage across the zener diode is close to constant over a wide range of currents thus making it useful as a shunt voltage regulator. In this article, we are going to explain zener diode and its applications in. The zener diode is used in its reverse bias or reverse breakdown mode, i.
Thus we will connect the zener diode parallel to the load such that the applied voltage will reverse bias it. They provide a lowcost and no frill method for voltage regulation. The zener diode specially made to have a reverse voltage breakdown at a specific voltage. The zener diode is like a generalpurpose signal diode. Career point cares zener diodes are a special kind of diode which permits current to flow in the forward direction. We use zener diodes for voltage regulation and voltage stabilisation. Characteristics figure 1 shows the current versus voltage curve for a 5. The forward characteristics of zener diode are similar to that of normal pn junction diode. This page describes the voltage regulator with the use of zener diode with its constructional details and working principle.
From the iv characteristics curve above, we can see that the zener diode has a region in its reverse bias characteristics of almost a constant negative voltage regardless of the value of the current flowing through the diode. Exploiting this characteristic of zener diodes allows for simple, inexpensive voltage regulators. Zener diode, resistor, variable dc power supply, milliammeter, voltmeter, rheostat and wire. Sep 20, 2017 so i am very curious why a zener diode a regular npn transistor and a mosfet transistor could not be used as a switching regulator. The purpose of load regulation is regulating output voltage when theload changes. While regular diodes get damaged when the voltage across them exceeds the reverse breakdown voltage, zener diodes work exclusively in this region. This is an example of a primary application of zener diodes voltage regulation. The output of the transformer is then rectified using a diode bridge and smoothened using a capacitive filter. The collector of the npn could be wired to the gate of the mosfet. Sep 20, 2018 zener diode as voltage regulator regulation.
A zener diode is one of the specially designed diodes that predominately works in reverse biased conditions. I guess you already know that a diode acts as a oneway passage of electricity. The range after the zener knee breakdown voltage until the rated voltage of a zener diode is reached is called the zener region. But when it is reverse biased above a certain voltage known as zener breakdown voltage or zener voltage or avalanche point or zener knee voltage the voltage remains constant for a wide range of current clarence zener is the scientist who discovered this electrical property. The zener diode working principles and its various.
Sep 12, 2015 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. This simple zener diode circuit is widely used as an easy method of providing a voltage reference. Zener diode can function as a voltage regulator when it is presented in a given circuit. Zener diodes are widely used as shunt voltage regulators to regulate voltage across small loads. The zener voltage regulator consists of a current limiting resistor r s connected in series with the input voltage v s with the zener diode connected in parallel with the load r l in this reverse biased condition. The reverse breakdown region is the vi characteristic of zener diode above zener breakdown voltage. A series resistancer is placed between a higher voltagev in and it is used to limit the current to the load and zener diode. Zener diode circuit for psu with series transistor. This particular property of zener diodes makes it useful as a voltage regulator. Because of its unusual properties it fills a longstanding need in electronic circuitry.
Apr 15, 2020 so, the diode will keep the fixed voltage 0. The zener diode working principles and its various applications. For instance, a change of 1 v in voltage can cause the current to increase by 10. But when it is reverse biased above a certain voltage known as zener breakdown voltage or zener voltage or avalanche point or zener knee voltage the voltage remains constant for a wide range of current. The load voltage equals breakdown voltage vz of the diode. Zener diode working, characteristics and application as voltage regulator by ajay kumar zener diode is a special kind of diode which permits the flow of current in the forward direction as well as in reverse direction when the voltage is above a certain voltage known as breakdown or zener voltage. This application of the zener diodes relies heavily on the ability of the zener diodes to maintain a constant voltage irrespective of variations in supply or load current. The stabilised output voltage is always selected to be the same as the breakdown voltage v z of the diode. A zener diode is a diode that breaks down at a specific voltage when it is reverse biased. We call this particular regulator circuit the shunt. It all works because we also think in terms of the. Contents1 line regulation2 load regulation 3 linear and switching voltage regulator3.
I know that it would be better to use amplifiers, et cetera, but im just trying to understand how this circuit works. The zener diode mainly operates in reverse biased condition. The main use of zener diode lies in the fact that the voltage across a zener diode remains constant for a larger change in current. The circuit shows an ac source fed to a stepdown transformer. Building a voltage regulator with an ideal zener diode, construction of a voltage regulator is easy, simply connect the diode between the unregulated voltage and ground. A special type of pn junction diode that operates in reverse biased condition, more specifically in breakdown region is known as zener diode. Here is how you can offer your support to all the work of the electric. The vi characteristics of a zener diode is as shown in the figure below. Jan 02, 2019 the zener diode mainly operates in reverse biased condition. It provides, among other useful functions, a constant voltage reference. Zener diode as a voltage regulator working principles byjus.
Dec 14, 2012 zener diode is a general purpose diode, which behaves like a normal diode when forward biased. Zener diode working, characteristics and application as. Help understanding a zener diode as a voltage regulator. This application of the zener diodes relies heavily on the ability of the zener diodes to maintain a constant voltage. The zener diode can work as a voltage regulator if it is introduced in a circuit. In our previous articles, we explain in detail about diodes, pn junction diode, semiconductors etc. In line regulation output voltage is regulated when the input voltage changes. Zener controlled transistor shunt voltage regulator the image below shows the circuit diagram of a shunt voltage regulator. Regulator zener diode regulator for low current power supplies a simple voltage regulator can be made with a resistor and a zener diode connected in reverse.
Let us say if zener voltage of 5 v is used then, the voltage becomes constant at 5 v, and it does not change. So i am very curious why a zener diode a regular npn transistor and a mosfet transistor could not be used as a switching regulator. Zener diode theory introduction the zener diode is a semiconductor device unique in its mode of operation and completely unreplaceable by any other electronic device. The maximum load current drawn from this circuit ensuring proper functioning over the input voltage range between 20 and 30 volts is. The primary objective of the zener diode as a voltage regulator is to maintain a constant voltage. Zener diodes are used in circuits to maintain a fixed voltage across a load. A voltage regulator is a circuit used to maintain a constant output voltage at a load independent of changes in the load current. The basic diagram of zener diode as voltage regulator is given below. We all know that in case the voltage across the diode is greater than a specific value it may well draw abnormal current from the source.
Zener diode operation and applications ece tutorials. The zener diode will continue in regulating the voltage till the zener diode current falls below the minimum i z min value in the reverse breakdown region. The working principles of zener diode is in the breakdown region. This breakdown voltage is known as the zener voltage. Zener diodes have a sharp reverse breakdown voltage and breakdown voltage will be constant for a wide rang of currents. Zener diodes are commonly employed in applications as voltage regulators. The zener diode provides the reference voltage, but a series resistor must be in place to limit the current into the diode otherwise a large amount of current would flow through it and it could be destroyed. Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. It will allow current to flow in a particular direction forward bias but it will prevent current to flow in the reverse direction reverse bias. Please login if you have an account or else signup for free. The most basic zener diode circuit consist of a single zener diode and a resistor. Nov 08, 2008 an 8v regulator with a 12v source that requires 1a of current requires a 250.
There are several drawbacks, however, that will be discussed shortly. As we know if the voltage across the diode exceeds a certain value it would draw excessive current from the supply. Let us first comprehend how a zener diode works before we understand zener diode as a voltage regulator. It is different from others diodes zener diodes will also allow current to flow in the reverse direction when the voltage is above a certain value. Due to this feature, it is used as a voltage regulator in d. The zener diode is connected across the base and the. The very simple zener diode circuit providing the shunt regulator function as shown above is not particularly efficient and is not practicable for many higher current applications. Its characteristics are otherwise very similar to common diodes. Zener diode regulator procedure step 1 monitor and report the load voltage v l by using the scopy voltmeter instrument to measure v l for r l equal to. Zener diode as voltage regulator and its vi characteristics. Zener diode is a special kind of diode which permits the flow of current in the forward direction as well as in reverse direction when the voltage is above a certain voltage known as breakdown or zener voltage. 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. Oct 15, 2017 the zener diode is used to regulate the base voltage which leads to regulated emitter voltage.
Simple zener diode circuit providing reference voltage. The voltage across load resistor r l is equal to the zener breakdown voltage v zkregardless of the value of load resistor r l or source voltage v s provided, of course, that the zener diode is in breakdown. Hbd854 zener theory and design considerations handbook. We can connect a lot of the number of diodes in series. This makes it possible to use a zener diode as a constant voltage device or a voltage regulator. The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting. Voltage regulation is classified into line regulation and load regulation. The zener diode then acts to regulate the output voltage to the zener voltage 10v.
In this region, a small change in voltage leads to a large change in current. Zener diode as a voltage regulator linkedin slideshare. When connected in parallel with a variable voltage source so that it is reverse biased, a zener diode conducts when the voltage reaches the diode s reverse breakdown voltage. A regular diode will not work effectively as a zener diode,and vice versa. Zener diode as a voltage regulator working principles. The doping level of the zener diode is somewhat higher than the normal pn junction diode so that it can provide a sharp breakdown voltage. Jan 02, 2019 the depletion region in zener diode goes back to its normal state when the reverse voltage gets removed. The zener breakdown voltage is the minimum reverse biased voltage below which the diode. Zener diode makes for a lousy regulator bald engineer. Placing the zener diode in parallel with the load as shown in figure 3. To construct a zener diode voltage regulator and measure its line and load regulation.
Since the exploited property of zener diodes is the reverse breakdown voltage, connect the anode of the diode to ground, not the cathode. Typically, zener diodes are only available at up to 5w, so in even a medium voltagecurrent application like this example, it may be more practical to use an integrated circuit regulator. The breakdown region voltage of a zener diode is set by carefully controlling the doping level during manufacture. Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits. Zener diodes are rated by their breakdown voltage v z and maximum power p z typically 400mw or 1. Zener diode finds application as voltage regulator and clipping circuit. Dec 16, 2015 zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits. The output along the diode is going to be constant.
In a dc circuit, zener diode can be used as a voltage regulator or to provide voltage reference. How does a zener diode and a resistor regulate voltage. The circuit could be arranged in such a way that the diode would allow voltage in excess of its nominal vz into the gate of the npn transistor. May 21, 2016 the breakdown region voltage of a zener diode is set by carefully controlling the doping level during manufacture. A zener diode makes for a lousy voltage regulator, but an excellent voltage.
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