Zener Diode-basic-Operation-and-Applications

A Zener diode is a silicon semiconductor device that permits current to flow in either a forward or reverse direction. The diode consists of a special, heavily doped p-n junction, designed to conduct in the reverse direction when a certain specified voltage is reached.

Figure 1 : A schematic image of a Zener diode

The Zener diode has a well-defined reverse-breakdown voltage, at which it starts conducting current, and continues operating continuously in the reverse-bias mode without getting damaged. Additionally, the voltage drop across the diode remains constant over a wide range of voltages, a feature that makes Zener diodes suitable for use in voltage regulation.

Zener diode operation

The Zener diode operates just like the normal diode when in the forward-bias mode, and has a turn-on voltage of between 0.3 and 0.7 V. However, when connected in the reverse mode, which is usual in most of its applications, a small leakage current may flow. As the reverse voltage increases to the predetermined breakdown voltage (Vz), a current starts flowing through the diode. The current increases to a maximum, which is determined by the series resistor, after which it stabilizes and remains constant over a wide range of applied voltage.

Zener Diode Basic Operation and Applications Figure 1

Figure 2: Zener diode IV characteristics

Zener breakdown

The breakdown is either due to the Zener breakdown effect that occurs below 5.5 V, or impact ionization that occurs above 5.5 V. Both mechanisms result in the same behavior and do not require different circuitry; however, each mechanism has a different temperature coefficient.

The Zener effect has a negative temperature coefficient while the impact effect experiences a positive coefficient. The two temperature effects are almost equal at 5.5 V and cancel out each other to make the Zener diodes rated at around 5.5 V the most stable over a wide range of temperature conditions.

Zener diode specifications

Zener diodes vary in specifications such as nominal working voltage, power dissipation, maximum reverse current, and packaging. Some commonly used specifications include:

Voltage Vz: The Zener voltage refers to the reverse breakdown voltage—2.4 V to about 200 V; can go up to 1 kV while the maximum for the surface-mounted device (SMD) is about 47 V).
Current Iz (max.): Maximum current at the rated Zener voltage Vz—200 uA to 200 A).
Current Iz (min.): Minimum current required for the diode to break down—5 mA and 10 mA.
Power rating: The maximum power the Zener diode can dissipate; given by the product of voltage across the diode and the current flowing through. Typical values are 400 mW, 500 mW, 1 W, and 5 W; for surface mounted, 200 mW, 350 mW, 500 mW, and 1 W are typical.
Voltage tolerance: Typically ±5%.
Temperature stability: Diodes around 5 V have the best stability.
Package: Leaded devices and the surface mount either as discrete devices or within integrated circuits.
Zener resistance (Rz): The diode exhibits some resistance as evident from the IV characteristics.

Zener Diode Basic Operation and Applications Figure 2

Figure 3: Zener diode resistance

Zener diode applications

Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits.

Voltage regulator

The load voltage equals breakdown voltage VZ of the diode. The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting.

Zener Diode Basic Operation and Applications Figure 3

Figure 4: Zener diode shunt regulator

Zener diode in overvoltage protection

If the input voltage increases to a value higher than the Zener breakdown voltage, current flows through the diode and create a voltage drop across the resistor; this triggers the SCR and creates a short circuit to the ground. The short circuit opens up the fuse and disconnects the load from the supply.

Zener Diode Basic Operation and Applications Figure 4

Figure 5: SCR overvoltage crowbar circuit

Zener Diode Clipping Circuits

Zener diodes are used to modify or shape AC waveform clipping circuits. The clipping circuit limits or clips off parts of one or both of the half cycles of an AC waveform to shape the waveform or provide protection.

Zener Diode Basic Operation and Applications Figure 5

Figure 6: Zener diode clipping circuits

Team Work - Meaning and Tips for better Team Work

A single brain is not always capable of making key decisions on its own. To come up with an efficient solution, an individual requires the help and advice of others. A team is established when individuals get together on a common platform with the common goal of completing a task. To guarantee optimum compatibility, team members should ideally come from similar backgrounds and have a single aim. To provide their best, the team members must complement each other and function as a single unit in tight cooperation. "There is no I in Team Work," as the saying goes, and each member must put the needs of his team first. Personal interests must take a second seat. Any team's performance is directly proportionate to the relationship between its members and their combined efforts. What is the definition of teamwork? Teamwork is defined as the sum of each team member's efforts toward the fulfilment of the team's goal. In other words, any team's backbone is its ability t

Scientists discover a new theory / The fundamental property of light – 150 years after Maxwell

Light plays a vital role in our everyday lives and technologies based on light are all around us. So we might expect that our understanding of light is pretty settled. But scientists have just uncovered a new fundamental property of light that gives new insight into the 150-year-old classical theory of electromagnetism and which could lead to applications manipulating light at the nanoscale. It is unusual for a pure-theory physics paper to make it into the journal Science. So when one does, it’s worth a closer look. In the new study, researchers bring together one of physics' most venerable set of equations – those of James Clerk’s Maxwell’s famous theory of light – with one of the hot topics in modern solid-state physics: the quantum spin Hall effect and topological insulators . To understand what the fuss is about, let’s first consider the behaviour of electrons in the quantum spin Hall effect. Electrons possess an intrinsic spin as if they were tiny spinning-tops,

19 Types Of Content Writing Services For Your Business

It’s hard to know which type of content writing service is the best for your business. There are so many different types of content writing services out there that it’s easy to get confused. You end up wondering if you’re choosing the right one for you. In this post, we’ll get rid of this confusion, once and for all. I’m going to list out the different kinds of writing services you could use. By the end of this article, you’ll know whether you need a copywriter, a content writer, or a social media marketer and how they can help you achieve your business goals. This post is also useful for writers who want to hone their writing skills in a specific area. Let’s dive in and learn what types of content writing services exist and when you should use them. (Bonus – if you want to hire the top 1% of writers, go to the bottom to learn how). Types of Content Writing Services As we go through the list of content writing services, you will find that many of them overlap. That’s perfectly

The LimitlessX - Get Tech Science News around the Globe

Search This Blog