What is Zener diode ? what do you know about Zener Diode and its Working function ?

                            Zener Diode

                         A properly doped crystals diode which has a sharp breakdown voltage is known as Zener diode.

The circuit symbol and characteristics curve of a zener Diode is shown below,

Circuit symbol (Image taken from google image)

                        The forward characteristics of a zener is similar to that of an ordinary diode.The reverse characteristics exhibits a region in which the voltage across the diode is almost independent of diode current. This fact makes 

Zener Diode useful as a voltage 

regulator device.

Characteristics curve of zener diode (image taken from google image)

• Manufacturers generally specify Zener diodes according to their Zener voltage (Vz) and maximum allowable power dissipation Pz.                                                                                                       If Vz is the voltage of the Zener Diode then maximum rated current,                                                          
                            Iz_{max = (Pz/Vz)                                                                                                                                          If current through Zener exceeds Izm, it will be destroyed.}
• _{Another parameter of interest is knee current which correspond to the knee of reverse characteristics curve. Below the knee current}  Iz_{min , Zener fail to regulate output voltage.}

         Zener Diode as a Voltage Regulator

                            In a voltage regulated power supply, the output voltage is constant and its independent of variation of input supply voltage and load current. The circuit diagram of a Zener diode voltage regulator is shown below.

Principle of Working

In the breakdown region, the output across the zener diode is almost independent of current through it. Hence zener diode maintain a constant output voltage V₀ ≈ V_{z , independent of variation of load current (Load regulation) or variation of input voltage}   V_{i   (Line Regulation) as along as the diode is at break down region.}

_{Variation of Output Voltage with Load current}

                        _{To discuss this we take Vi remains constant and} I_{L to vary, Since} V₀ ≈ V_{z , across Zener is fixed; it is independent of}  I_L

  _. 

                         _{Thus if load current (}I_{L) increases, when the supply voltage is fixed, the Zener current}   Iz decreases by the same amount ; but V₀ ≈ V_{z   remain constant.}

_{Variation of Output Voltage with Input Voltage}

                             _{We take now}  I_{L ,}R_{L remains constant and} V_{i   varying. Since} V_{0  tends to remain constant at Vz,}  I_{L remains constant.}

_{i.e. In this case Zener current and total current change such ways as to maintain}  I_{L constant and hence to constant i.e.} V_{0 =}I_LR_{L . to be constant.}