Zener diode

 Zener diode 

The zener diode is a silicon p-n junction semiconductor device, which is generally operated in it reverse break down region. The zener diode are fabricated with precise breakdown voltage by controlling the doping level during manufacturing. 

                       Symbol of zener diode 

Characteristics of zener diode

The forward biased condition,the normal rectifier diode and the zener diode operate in similar. But the zener diode is designed to be operated in the reverse biased condition.  In reverse bias  condition,the diode carries reverse saturation current till the reverse voltage applied is less than the reverse breakdown voltage.when the reverse voltage excess reverse breakdown voltage, the current through it change drastically but the voltage across it remains almost constant. Such breakdown region is a normal operating region for zener diode.

The breakdown characteristics for a zener diode is significantly important, as the is an operating region for the diode.wgen the reverse voltage applied to a zener diode is increased,  initially the current through it is very small,of the order of few less. This is reverse leakage current of the diode, denoted by io.the change from a low value to large value of current  is very sharp and well defined. Such a sharp change in the reverse characteristics is called knee of the curve . This reverse  bias voltage at which the breakdown occurs is called zener break down voltage.

The voltage  vz is set by carefully ccontrolling  to the knee point is called zenervknee cirrent and it is a minimum current zener must carry to operate in reverse breakdown region. It is denoted by izk.

Form the bottom of the knee the zener break down voltage remains almost constant,  through it increase slightly as the zener current iz, increase the current at which the nominal zener break down voltage is specified is called zener test current  ,denoted as izk.

The conduction in zener is opposite to that of arrow in the symbol,as operated in breakdown region.the power dissipation is very low. Dynamically zener resistance is very small in reverse breakdown condition.

            V-I characteristics of zener diode 

Application 

Voltage regulator

Voltage limiters

Protection circuit