The diode is one of the most common components in every electronic circuitry. You already know that a diode is a semiconductor device made of positively and negatively doped parted being fitted together. The region where the p and n-type meet are referred to as a junction. Zener diode is a special type in that it allows current to flow forward as well as reverse biased conditions. In a forward-biased state, it acts as a normal diode conducting when the voltage across it raises above 0.7V. In a reverse-biased state, it is able to conduct when the reverse voltage is about 5V. once it starts to conduct, current increases up to a maximum value only limited by circuit resistance while voltage remaining constant. This is a great behavior in engineering as we will see.
Two heavily doped p and n-type semiconductors are brought together forming a thin layer of the p-n junction. Two terminals are made, one in p-type and the other on n-type semiconductors. When forward-biased p-type is connected to the positive source of power and n-type on the negative source. It is a small component, mostly cylindrical in shape. To identify the terminals, the cathode side has a line of different colors near it on the curved surface.
The diode usually operates in reverse biased mode, the p-type on the cathode and the n-type on the anode. When voltage is applied, a small leakage current flows in the PN junction. As the voltage in increases the leakage current increases and at about 5 volts the junction breakdown and becomes conductive. This is called the Zener effect after the scientist who discovered it. At this voltage-free electrons on n types are attracted by a high electric field across the thin junction and they tunnel through hence current flows. The current continues to increase as the breakdown is affected while the voltage across it remains fairly constant with varying applied voltage, the Zener voltage. The diode becomes conductive and the current is only limited by circuit resistance. The advantage of this is when connected in parallel with the load, the load voltage will be the same as Zener voltage a constant value despite varying applied voltage. It’s worthy to note that, this item still undergoes the normal avalanche breakdown of the depletion layer at a higher voltage than Zener breakdown which destroys it.
The most important information about a device after knowing it function is the ratings. The environment in which it operates. The following are worth of consideration;
Voltage – the rating ranges from 2.4V to 200V and special ones are designed for 1000V.
Current- the minimum current should know, usually it ranges from a minimum of 5 microamperes to 200A minimum to maximum.
Power rating- this is the product of current and voltage, ranging from 400 microwatts to 5 watts.
Voltage tolerance- usually very low about 5 %
Resistance – this is the effective resistance across it, the smaller the better.
Finally, we get to know areas where Zener diode is used, some of them are given below.
- Voltage regulation- this is the most common area. The load is sensitive to variable source voltage and can cause malfunction. The diode maintains constant input voltage to load when connected in parallel. The Zener effect is applied.
- Overvoltage protection- this may be used in surge protection devices. When a voltage above the desired one appears at the input, the diode undergoes Zener breakdown, becomes conductive and the current form is used to trigger an electronic switch that cuts off the power supply to load.
- Clipper circuit- when output voltage should not exceed a certain value with varying input, the diode is used to clip the value above the Zener voltage. The circuit is used in square wave generators among other uses.
- Reference voltage in amplifiers- the constant output voltage is used to make a reference of adjusting input voltage so that it can much the voltage across the diode.
Electronics is interesting, have you appreciated how a simple small device achieves great functions. Zener diode is really a simple solution to voltage regulation needs, overvoltage protection, and reference voltage source. By leveraging the reverse bias operation, we have seen how the diode is an important component. The forward bias conducts and reverse bias conducts without destruction in Zener diodes. For your practice, get the item at your nearest electronic parts seller and get to the lab.