Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. Zener diode is often used as a shunt voltage regulator. In the second circuit of Figure 1, a zener or avalanche diode is used, and an appreciably higher output voltage realized. When the voltage across the terminals of a Zener diode is reversed and the potential reaches the Zener Voltage (knee voltage), the junction breaks down and the current flows in the reverse direction. This article will help to explain the characteristics which make up zener diodes, specifically how the voltage across a zener diode varies with the current flowing through it. The I-V Characteristics Curve of a zener diode, shown below, is the curve which shows the current-voltage relationship of a zener diode. The processes which are responsible for current conduction in a reverse-biased diode are called as Avalanche breakdown and Zener breakdown . Zener Diode Characteristics. These diodes exhibit a controlled breakdown which allows the current to keep the voltage across the Zener diode close to the zener breakdown voltage. Zener diode as a Voltage Regulator. A Zener diode, when reverse biased (as shown in the circuit) has a constant voltage drop across it irrespective of the current flowing through it. Zener diode is a semiconductor device that allows current to flow in a forward or reverse direction. 1. A Semiconductor Diode blocks current in the reverse direction but will suffer damage if the reverse voltage applied across becomes too high. The voltage across the Zener diode remains constant beyond Zener voltage and hence, the same/constant regulated voltage is obtained across RL. Reverse Bias – The voltage potential is connected negative, (-ve) to the P-type material and positive, (+ve) to the N-type material across the diode which has the effect of Increasing the PN junction diode’s width. This constant voltage drop across the Zener diode produced by reverse breakdown is represented by a DC voltage symbol. Zero Bias – No external voltage potential is applied to the PN junction diode. Thus, as long as the Zener current ( I Z ) is above a certain level (called holding current), the voltage across the Zener diode ( V Z ) will be constant. Because the avalanche breakdown is uniform across the whole junction, the breakdown voltage is nearly constant with changing current [clarification needed] when compared to a non-avalanche diode. A Zener diode is a specially designed diode that has a reduced breakdown voltage called the Zener voltage. The voltage across the diode remains reasonably constant at this time. Let us say if Zener voltage of 5 V is used then, the voltage becomes constant at 5 V, and it does not change. A zener diode of break down voltage V z is reverse connected to an input voltage source V i across a load resistance R L and a series resistor R S. The voltage across the zener will remain steady at its break down voltage V Z for all the values of zener current I Z as long as the current remains in the break down region. If the Zener diode’s voltage is 12.6 volts and the power supply’s voltage is 45 volts, there will be 32.4 volts dropped across the resistor (45 volts - 12.6 volts = 32.4 volts). It is easy to see that for the given range of voltages (80 − 120 V), the voltage across the zener is greater than VZ (= 50 V). (iii) Zener diode is used as a voltage regulator. A Zener Diode, also known as a breakdown diode, is a heavily doped semiconductor device that is designed to operate in the reverse direction. 32.4 volts dropped across 1000 Ω gives 32.4 mA of current in the circuit. The Zener diode exhibits an apparently similar effect in addition to Zener breakdown. Now if accidentally voltage at the gate of MOSFET exceeds 5v, breakdown of the diode occurs and all the current flows through the diode to ground. Principle: Zener diode is operated in the reverse breakdown region. This constant-voltage characteristic leads to a number of applications of diode under reverse bias condition. Simple Zener diode circuit providing reference voltage. Hence the zener diode will be in the “on” state for this range of applied voltages. The primary objective of the Zener diode as a voltage regulator is to maintain a constant voltage. The voltage change for … Zener Diode Explanation While true zener breakdown occurs below 5 V, avalanche breakdown occurs at higher voltages and has a positive temperature coefficient. To reverse bias the load, a Zener diode is connected parallel to it, and after the Zener diode surpasses knee voltage, the voltage across the load becomes constant. The breakdown voltage of this Zener is 5.1 volts. The voltage drop across the diode always remains constant irrespective of the applied voltage, and this feature of the Zener diode makes it suitable for voltage regulation. This means that for slight changes in current, there will be a small change in the voltage across the diode. A Zener diode operating in breakdown acts as a voltage regulator because it maintains a nearly constant voltage, which is equal to the Zener voltage, across its terminals over a specified range of reverse-current values. When connected in parallel with a varying voltage source, such as the diode rectifier we just discussed, so that it is reverse biased, the zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. The zener diode and decoupling capacitor develop a perfectly clean voltage at the base of the transistor, which is replicated at the output generating a virtually noise free volatge. 3. The first step is to determine the state of the zener diode. Thus preventing the MOSFET from getting destroyed. Zener resistance Rz: The IV characteristic of the Zener diode is not completely vertical in the breakdown region. 2. 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