Fri. Jul 19th, 2024

Zener Diode: An Overview


Forward conduction, reverse cut-off, and excessive reverse voltage will cause breakdown and damage to typical diodes. A Zener diode is a surface junction semiconductor diode that is made using a unique procedure. It has the same forward characteristics as regular diodes, but it has unique reverse features. Its most notable characteristic is its ability to operate safely in the reverse breakdown state, with the voltage remaining basically constant over a wide range of current variations in reverse breakdown conditions. The Zener diode’s primary function in the circuit is to regulate voltage and provide a reference voltage.Zener diode characteristics


In the following part, Easybom will give an elaborate introduction to Zener diode characteristics.

For ordinary diodes, forward conduction, reverse cut-off, and excessive reverse voltage will cause breakdown and damage. The Zener diode is a surface junction semiconductor diode manufactured by a special process. Its forward characteristics are the same as ordinary diodes, but its reverse characteristics are special. Its biggest feature is that it can work stably in the reverse breakdown state without damage, and the voltage remains essentially constant over a wide range of current variations in reverse breakdown conditions. The Zener diode mainly plays the role of regulating voltage and providing reference voltage in the circuit.

The reverse breakdown state of the PN junction is used in the Zener diode to ensure that the current can shift over a wide range while the voltage remains constant. Up to the crucial reverse breakdown voltage, this diode is a semiconductor device with an extremely high resistance. The reverse resistance reduces to a minimal value at this important breakdown point, and the current increases in this low resistance region while the voltage remains constant, grading the Zener diode according to the breakdown voltage. Greater voltages can be obtained by connecting zener diodes in series, and higher regulated voltages can be obtained by connecting in series. Zener diodes, like Schottky diodes, are significant electrical components, and their performance in terms of power protection may be equivalent.
Symbol of Zener diode in the circuit diagram


Zener diode symbol

Characteristics of a zener diode


Easybom will go through Zener diode properties in detail in the following section.


Zener Diode as Voltage Regulator


Zener diode has a very high resistance up to the critical reverse breakdown voltage. It can be used to produce a regulated voltage output with low ripple under varying load current conditions. Bypassing a small current from the voltage source through the diode, through a suitable current limiting resistor (RS), the Zener diode will conduct enough current to maintain the voltage drop Vout.

Note: The Zener diode works in the range A-B in the figure. The steeper the line is, the better the performance is. IZ(min) and IZ(max) are the minima and maximum working currents of the Zener diode when it works in the normal voltage regulation state. When the reverse current is less than IZ(min), the Zener diode is in the reverse cut-off state and the voltage regulation characteristic disappears; when the reverse current is greater than IZ (max), the Zener diode may be burned.


Resistor RS is in series with the Zener diode as a voltage regulator to limit the current flow through the diode, Vs is connected in combination. The regulated output voltage Vout is taken from the Zener diode. The cathode terminal of the Zener diode is connected to the positive rail of the , so it is reverse biased and will operate in its breakdown state. Resistor RS is chosen to limit the maximum current flowing in the circ

The load is in parallel with the Zener diode, so the voltage on RL is always the same as the Zener voltage, (VR = Vz). There is a minimum Zener current for which stabilization of the voltage is effective and which must always remain above that value for operation with a load within its breakdown region. The upper limit of the current will of course depends on the power rating of the device. The supply voltage VS must be greater than VZ.


There is a small problem same with the Zener diode stabilizer circuits. The diode can sometimes generate electrical noise on top of the DC power supply as it tries to stabilize the voltage. Usually, this is not a problem for most applications, but it may be necessary to add a decoupling capacitor a large value at the Zener output terminal to provide additional smoothing.


Applications of Zener diode

With no load connected to the circuit, the load current will be zero, (IL = 0), all circuit current is going through the Zener diode, which in turn dissipates its maximum power. A small fraction of the load resistor RL and RS are connected, which will cause a larger diode current as a result of the increase of the power dissipation requirements of the diode. Care must be taken in choosing the appropriate series resistance value to make sure that the maximum rating power of the Zener diode not be exceeded under the no-load or high-impedance conditions.

In the following part, Easybom will introduce the applications of Zener diode in the surge protection circuit, overvoltage protection circuit in the TV, arc suppression circuit, and series voltage regulation circuit.


  1. Surge protection circuit (as shown in Figure 1):



The Zener diode breaks down at an accurate voltage, which makes it useful as a limiting or protection component because Zener diodes of vvoltages are available, so it is especially suitable for this application. The diode D in the figure is used as an overvoltage protection device. As long as the power supply voltage VS exceeds the voltage regulation value D of the diode, it will be turned oy J pulls in the load RL and separates it from the power supply.


  1. Overvoltage protection circuit in the TV (as shown in Figure 2):



EC is the main supply voltage of th too high, D is turned on, the transistor BG is turned on, and its collector potential will be changed from the original high level (5V) to low level, and the TV enters the standby protection state through the control of the standby control line.


  1. Arc suppression circuit is shown in Figure 3:



If a suitable Zener diode is connected in parallel to the inductance coil when the coil is cut off in the conduction state, the high voltageagnetic energy is absorbed by thediode, so when the switch is turned off, the arc of the switch is eliminated. This application circuit is widely used in industry, such as some high-power electromagnetic suction control circuits.


  1. Series voltage regulation circuit (as shown in Figure 4):



In this circuit, the base of the series regulaner diode D, then its emitter outputs a constant 12V voltage. This circuit is applied in many situations.


In addition to the Zener diode functions mentioned above, Zener diodes can also be used for one-time protection circuits. It can be used in reverse parallel connection to inhibit the voltage from increasing to damage valuable equipment in important locations. When the power supply fails, after the voltage regulaor of the Zener diode is exceeded, it will quickly turn from the cut-off state to the reverse break down, causing short-circuit the power supply directly to protect all loads in the power supply branch from damage due to overvoltage. Because this type of Zener diode for protection does not work at ordinary times, it can be temporarily not used in emergency maintenance. Experienced maintenance personnel can even use local materials in emergencies, and can be flexibly used as maintenance tools after disassembly and assembly.


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