What is a zener diode and how does it work? | Intermediate Electronics

So, what is a Zener diode? And how is it different from a typical diode? Or have you ever wondered why we operate a Zener in reverse bias unlike normal diodes that is operated in forward bias? This is because Zener diodes are meant to ‘break down’. Most of us are familiar with general-purpose and rectifier diodes. However, there are several other types of diodes that are designed for special purposes. One of these is the Zener diode. So, what is a Zener diode and how it is different from a typical diode? A Zener diode is a silicon pn junction device that allows current to flow not only in the forward direction like a typical silicon or germanium diode, but also in the reverse direction if the voltage is greater than the breakdown voltage known as Zener knee voltage or simply Zener voltage, named after Clarence Melvin Zener, the discoverer of this electrical property. The schematic symbol for a regular diode has a straight line representing the cathode, while the Zener diode has a bent line that resembles the letter Z (for zener). It makes a lot of sense, right? Zener diodes act like normal diodes when forward-biased. However, they are designed to allow current to flow in reverse once the reverse voltage equals its rated Zener Voltage. Unlike ordinary rectifier diodes, which are never intended to be operated at or near breakdown, a Zener diode is designed to operate in the breakdown region. Breakdown of a diode happens when you apply a reverse bias 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. This constant voltage drop across the Zener diode produced by reverse breakdown is represented by a DC voltage symbol. To understand more how Zener diodes operate, let’s look at two types of reverse breakdown in a Zener diode: avalanche and Zener breakdown. The avalanche effect occurs in both rectifier and Zener diodes at a sufficiently high reverse voltage. On the other hand, Zener breakdown occurs in a Zener diode at low reverse voltages. A Zener diode is heavily doped to reduce the breakdown voltage. This causes a very thin depletion region. As a result, an intense electric field exists within the depletion region. Close to the Zener breakdown voltage, the field is sufficiently able to pull electrons from their valence groups and create current. Zener diodes with breakdown voltages of less than approximately 5 V operate typically in Zener breakdown. Those with breakdown voltages greater than approximately 5 V operate typically in avalanche breakdown. Both types, however, are called Zener diodes. Zeners are commercially available with breakdown voltages from less than 1 V to more than 250 V with specified tolerances from 1% to 20%. As the reverse voltage is increased, the reverse current also increases until it reaches the Zener knee current. This time, the breakdown effect begins. The Zener impedance, which is the internal Zener resistance, begins to decrease as the reverse current increases rapidly. From the bottom of the knee, the zener breakdown voltage remains relatively constant although it increases slightly as the zener current IZ, increases. VZ is usually specified at a value of the Zener current known as the test current. Checkout the written tutorial on CircuitBread.com to learn even more about Zener diodes and the important specifications that affect their operation. When we do the practical tutorial on Zener diodes, we’ll need to understand these specifications to get the performance we want. As always, let us know if you liked this video in the comments or with a thumbs up. If you haven’t subscribed, that’s probably something you want to take care of. We’ll see you in the next video.

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Id: e65XnZyQ_Vc

Length: 3min 38sec (218 seconds)

Published: Tue Dec 10 2019