The reverse breakdown of a PN- junction may occur either due to Zener effect or avalanche effect. A standard 10 V Zener may have a temperature coefficient of +0.07%/ °C which may correspond to 7 mV/ °C variation in temperature. Zener diodes not only stabilize long-term voltage fluctuations, but also short-term fluctuations as they are caused by the residual ripple of a rectified, pre-smoothed AC voltage. In most circuit applications this may work as effectively as a typical smoothing capacitor having several thousand microfarads capacity, resulting in a significant reduction in the level of ripple voltage superimposed on the DC output. Full Wave Rectifier Name: Sanzhar Askaruly ID: 201100549 Date: 17/09/2014 Introduction Diode is an electronic device having conductor at their ends. Brief Theory: When a reverse-bias voltage is applied to a pn junction, the electric field in the space-charge region is increases. AIM. We will see that the voltage across the diode remains constant whereas the current through it keeps on increasing. In simple words, whenever the supply across the zener diode exceeds the rated zener value, the zener diode conducts and grounds the excess voltage. When this specific critical voltage is surpassed, the active resistance of Zener diode falls to an extremely low level. With your lab partner, brainstorm on the following ideas: The following graph shows the effect of the capacitor for reducing zener diode noise. 3 Basic Capacitor Functioning and Working Explored, How to Configure Resistors, Capacitors and Transistors in Electronic Circuits, IRF540N MOSFET Pinout, Datasheet, Application Explained, Half-Bridge Mosfet Driver IC IRS2153(1)D Datasheet,, Small Signal Transistor(BJT) and Diode Quick Datasheet. This allows a variable reference voltage to be adjusted at the base of the series transistor. 40 mA). In general, the cathode of a diode is marked by a solid line on the diode.The A zener diode Conducts excellently even in reverse biased condition. Do the same experiment by connecting the Zener diode in the forward bias. For that, we increase the reverse bias voltage slowly and in small steps. Zener diodes - named after its inventor Dr. Carl Zener are fundamentally used in electronic circuits for generating precise voltage references. A zener diode when reverse biased can either undergo avalanche break down or zener break down. ... For higher values of Zener voltage, TC is positive d) All of the mentioned. Zener diodes are designed in many wattage ratings and with voltage ratings which range from 2.7 Volts to 200 Volts. An easy way to increase zener diode power handling capacity is probably to just connect them in parallel as shown below: However, practically this may not be as simple as it looks and may not work as intended. When the AC supply moves across the positive half of the cycle, the zener doesn't conduct until the AC climbs up to the zener voltage level. We are going to learn about an experiment to find out the Zener breakdown voltage and draw the characteristics of Zener diode. UCSI University. Unlike ordinary PN junction diode, the reverse current in Zener diode is measured using milli-ammeter due to the large flow of current. Zener diodes are operated in the reverse break down region where diode is reverse biased. As the voltage rises into e reverse direction, initially very little current flows. Last Updated on December 18, 2020 by Swagatam 11 Comments. Excellent post. But in normal PN junction diodes, the breakdown voltage is comparatively high A quick way to counter this problem may be to add low values series resistors with each zener diodes as shown below, which will allow each zener diode to share the current uniformly through compensating voltage drops generated by the resistors R1 and R2: Although, the power handling capacity can be increased by connecting Zener diodes in parallel, a much improved approach may be to add a shunt BJT in conjunction with a zener diode configured as a reference source. A relay and an appropriately selected zener diode are enough to create an accurate low voltage or under voltage cut off protection circuit for any desired application. Observe the nearly constant voltage in the breakdown region. In case the current deviates from its original range, it creates a proportionate change in the biasing level of R3, which in turn causes the series transistor resistance to increase or decrease proportionately. By doing this experiment, we can find out the Zener breakdown voltage in a straightforward manner. Zener Diode Characteristics. The diagram shows a bridge network built using a pair of resistors and a pair of Zener diodes having identical characteristics. Previous: Calculating Transistor as a Switch, Next: Fiber Optic Circuit – Transmitter and Receiver. Theory: -A Semiconductor diode is prepared by joining P and N sections of a semi conducting material like germanium or silicon. Characteristics of the Diode Lesson 2. It is acting Course. Purpose: The objective of this experiment is to become familiar with the properties and uses of diodes. Construct the circuit. 2019/2020 Zener diodes can be also applied as effective ripple voltage filters, just as it's used for AC voltage stabilization. 3 Theory of experiment A Zener Diode is constructed for operation in the reverse breakdown re-gion.The relation between I-V is almost linear in this case V z = V z0 +I zr z, where r z is the dynamic resistance of the zener at the operating point.V z0 is the voltage at which the straight-line approximation of the I-V characteristic intersects the horizontal axis. When we apply a voltage more than the Zener breakdown voltage (can range from 1.2 volts to 200 volts), the depletion region vanishes, and large current starts to flow through the junction. Experiment 8 . when the voltage across the zener diode exceeds its zener voltage rating VZ) . Note down the current and voltage reading. V-I Characteristics of Zener Diode Zener Diode is a reverse-biased heavily-doped PN junction diode which operates in the breakdown region. Because, the signal is negative therefore the AC will be shorted via the anode to cathode of the zener, causing 0 V to appear the output. Zener Diode Code Identification: Zener Diodes have an additional letter which will appear after the numbers. In this circuit the Zener diode creates a reference voltage for the series pass transistor, which, essentially, works like an emitter follower. Note down this voltage separately. In this situation, suppose the input voltage increases to an extent that exceeds the Zener breakdown voltage - will force the Zener diode to conduct. Thank you Andrew, Glad you are loving my site, you can find the required details under this category:, In zener diode, electric current flows from both anode to cathode and cathode to anode. VOLTAGE-CURRENT CHARACTERISTICS OF A ZENER DIODE . Zener diode voltage-current characteristic The Zener diode has a normal forward characteristic where the current rises after the initial turn-on voltage is reached. The zener voltage ratings of the individual zener diodes should be best chosen for most of the applications. Populate the values in the table. The Zener diode mainly operates in reverse biased condition. In case you want the above circuit to provide a variable voltage regulated output, it could be easily achieved by using a 1K potentiometer across the Zener diode. Here, the voltage must be same as the ripple trough level. ELE 213 - Electronics Page 1 of 5 Lab #2 Experiment procedure A. Bridge Rectifier Circuit 1. Zener diodes are a special type of semiconductor diode– devices that allow current to flow in one direction only –that also allow current to flow in the opposite direction, but only when exposed to enough voltage. Record the measured value of each resistor. The advantage of this circuit is that it prevents the fuse from blowing frequently and unpredictably due to its close fusing value to the load current. Experiment No.4 Zener diode Characteristics Object: To study and measure the effects of forward and reverse bias on the zener diode current. As shown in the below example when an AC supply is used with a zener diode, the zener will instantly conduct as soon as the AC signal passes from zero towards the negative half of its cycle. Note down the voltmeter reading at this point. Externally, you may find zener diodes a lot similar to standard diodes such as 1N4148. Here Vz is the Zener breakdown voltage. Determine the maximum and minimum load current (Li), for example 10 mA and 0 mA. (Note that the ratio of the secondary voltage to the primary voltage equals the ratio of the number of turns in the secondary to the number of turns in the primary.) The typical value of V BE ... Zener diode is a P-N junction diode specially designed to operate in the reverse biased mode. The graph of voltage vs current of a diode is called its characteristic. Zener diodes generate noise while operating due to their junction avalanche effect while switching, ranging from 10 uV to 1 mV. Zener Diode characteristics: VI characteristics of Zener Diode. A Zener diode not only allows current to flow from anode to cathode but also, in the reverse direction on reaching the Zener voltage. Zener Diode Characteristics - Zener regulator Prelab: You are tasked to determine experimentally the characteristic curve of a reverse-biased Zener diode. Apparatus A Zener diode (with small reverse breakdown voltage of about 6 volts), [i.e., V z = 6 V], a ten volt battery, a high resistance rheostat, two 0-10 V voltmeter, one 0-100 mA ammeter, one 20 Ω. resistance, one way key, connecting wires. We should select a Zener diode with a breakdown voltage approximately equal to the voltage we need across the device. These are devices that are able to create a practically constant voltage across them regardless of variations in circuit and voltage situations. They provide a low-cost and no frill method for voltage regulation. Diodes . As indicated in the basic regulator design the required output voltage which is the equivalent Zener voltage Vz = 4.7 Volts, and the selected, The series resistor Rs must allow the minimum amount of current 10.1 mA even when the input supply is a the lowest specified level, which is 1.5 V higher than the selected zener value Vz, and may be calculated using Ohms law as: Rs = 1.5 / 10.1 x 10, If the supply voltage rises to 12 V, the voltage drop across Rs will be Iz x Rs, where Iz = current through the zener. We will build the zener diode circuit and zener diode circuit with load from Figure 5.1 (See Appendix) and Figure 5.2 (See Appendix) in lab and will observe and record the experimental values. If you keep doing so, after a particular value of reverse bias voltage, the value of current in A1 will spike suddenly. h) Bias Current (I2) Stability Noise 9 _:5% . Distinctive material, useful read. This letter denotes the tolerance of the zener voltages. The typical forward voltage at room temperature with a current of around 1 mA is around 0.6 volts. VI characteristics of zener diode The forward bias region of a Zener diode is identical to that of a regular diode. A characteristic zener diode for general purpose electronic circuits has the power rating of 500mW, BZX55 zener diode series or the larger 1.3W, BZX85 zener series are … The P type has excess number of holes while the N type has excess number of electrons. The Zener diode is rated at 400 mW, and the minimum Zener current is 5mA. Due to this the voltage drops below the zener voltage which switches OFF the zener, and the supply yet again tries to exceed the zener voltage, switching ON the zener yet again. Examining the Characteristics of Diodes . To find Zener Breakdown Voltage in reverse biased condition. 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