It is a type of diode that allows current to flow conventionally. The current flow from anode toward the cathode. When the anode is positive to the cathode in a diode. The voltage across the terminals is reversed. The potential reaches the Zener voltage, The junction point will breakdown and the current will flow in the reverse direction. This effect is called the Zener effect.
What is Zener Diode
Zener diodes are manufactured with different varieties of Zener voltages (Vz). Zener diodes have a heavily doped PN junction. A similar breakdown voltage is observed in general-purpose diodes. But the voltage and sharpness of the knee voltage are not clearly defined as in Zener diodes.
Normal diodes are not designed to work in the breakdown region and it can cause permanent damage to the device. Zener diodes are manufactured to operate quite precisely in the junction region.
It recovers fully from the junction breakdown. It is not being harmed in proper use. Zener reverse breakdown voltage is due to electron quantum tunneling. That is caused by a high-strength electric field.
However, many diodes described as Zener diodes instead of on the avalanche breakdown diode. Both breakdown voltage types are used in Zener diodes with the Zener effect shows at lower voltages and avalanche breakdown at high higher voltages.
Zener diodes are widely used in electronic devices of all kinds and the basic building blocks of electronic circuits.
They are used to generate low-power rails with stable high voltage and also provide reference voltages for circuits, especially stabilized power supplies.
They are also used to protect circuits from overvoltage, especially electrostatic discharge devices.
The operation of a Zener diode depends on the heavy doping of its PN junction. The depletion region formed in the diode is very thin even less than 1 µm. Its electric field is consequently very high (about 500 kV/m) even for a small reverse bias voltage of about 5 V It allows electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material.
In the emitter-base junction of a bipolar NPN transistor behaves as a Zener diode. Its breakdown voltage is about 6.8 V for common bipolar processes and about 10 V for lightly doped base regions.
The emitter-base Zener diodes can handle only a small amount of currents as the energy is dissipated in the base depletion region which is very small. The higher amount of dissipated energy causes thermal damage to the junction.
Uses of Zener
These are widely used as a voltage reference and as shunt regulators to regulate the voltage across small circuits in an electrical device.
When it is connected in parallel with a variable voltage source so that it is reverse biased A Zener diode conducts when the voltage reaches breakdown voltage.
Another application of the Zener diode is the use of noise that is caused by its avalanche breakdown voltage in a random number generator.
Zener is used:
- Used in clipping circuits
- As a voltage regulator
- Protects from overvoltage
- Used to shift voltage
Examples of a waveform clipperTwo Zener diodes facing each other in series clip both half cycles of an input signal. It is used not only to reshape a signal but also to prevent voltage spikes from affecting circuits that are connected to the supply voltage.
Examples of a voltage shifter
A Zener diode can be connected to a circuit with a resistor to act as a voltage shifter. This circuit low the output voltage that is equal to the Zener diode’s breakdown voltage.
Examples of a voltage regulator
A Zener diode can be connected in a voltage regulator circuit to regulate the voltage applied to a load, such as in a linear voltage regulator.