Introduction to Zener Diode
Definition: Zener Diode, also sometimes called the breakdown diode, is P-N junction diode specially designed for operation in the breakdown region in reverse bias condition. The diode may use either zener breakdown mechanism or avalanche breakdown mechanism. The breakdown diode may be silicon or germanium one but silicon is preferred over germanium because of higher operating temperature and current capability.The knee point is also more sharp in case of silicon zener diode.
Symbol of Zener Diode
Constructional diagram of Zener Diode with its construction
Construction: Zener Diode is like an ordinary P-N junction diode except that it is properly doped so as to have a sharp breakdown voltage. There are several methods to manufacture zener diodes, such as
- Diffused structure.
- Alloy diffused structure
Diffused structure zener diode consists of two N and P substrates diffused together and has metallic layers deposited on both sides to connect anode and cathode terminals. The limitation of this construction is that the edge of the junction is expected to be contaminated.
Alloy diffused structure of zener diode gives better zener characteristics at lower zener voltages. On the other hand diffused zener diode used at higher zener voltages.
Volt- Ampere characteristics of zener diode
Application of Zener Diode:
Zener Diode Shunt regulator or voltage regulator: Voltage regulation is a measure of circuit’s ability to maintain a constant output voltage even when either input voltage or load current varies.
Now how a zener diode can be used as voltage regulator to provide a constant voltage from a voltage source whose voltage may vary appreciably. A resistor ‘R’ is required to limit the reverse current through the diode to safer value. the voltage source ‘V’ and the resistor ‘R’ are so selected that the diode operates in the breakdown region.
The diode voltage in this region, which is also the voltage across the load is called zener voltage and the diode current is called zener current. The series resistor ‘R’ absorbs the output voltage fluctuations so as to maintain voltage across the load constant. Zener Diode is reverse connected across the input voltage whose variations are to be regulated.
As long as voltage across the load is less than breakdown voltage, the zener diode does not conduct, the resistor and load constitute a potential divider across V. As supply voltage V is increased, the voltage drop across load becomes greater than the zener breakdown voltage. It then operates in breakdown region.
When zener diode operated in breakdown region, the voltage across it, V remains fairly constant even though current ‘I’ flowing through may vary considerably.
This is all about the application of Zener Diode.
Other applications of zener diode:
- Meter protection
- Zener diode as peak clipper
- Switching operation
- Zener diode as reference element