What is Zener Diode, Formula, Operation, Breakdown, Voltage Regulator

What is Zener Diode

Zener diode is a type of semiconductor diode it operates under the reverse bias at line voltage reaches the breakdowns as called reverse bias voltage or knee voltage. So the current flow in reverse direction thus effect is called zener effect.

Zener v_S Diode

In electronic circuits the diode is one of basic components as used. The zener diode is one of the special properties of diode than used in special type of equipment. The regular used PN junction diode allow to flow current from anode to cathode in forward biasing only and to block current flow in reverse biasing. The zener diode is same like diode function in forward bias but in reverse bias current conduction from cathode to anode.

Construction of Zener

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The structure of zener diode in a many ways that’s are

Diffused structure
Passivated structure
Alloy diffused structure

we regularly used zener diode is diffused structure .The both p and n type layers are diffused together. Anode and cathode terminals are construct with metal layer. The junction area filled with silicon oxide layers for preventing the layers. the deplection layers are very thin it depends on level of doping stage.

Working Principle

Forward Bias

The zener diode is connecting in forward bias, positive terminal of the source is connected to the anode (A) and the negative terminal of the source is connected to the cathode (K). Given applied voltage are low small leakage current flows through the zener diode. Voltage is increased in breakdown the potential barrier is reduced and the current starts flowing in the circuit. This operation as same as semiconductor diode.

Reverse Bias

The zener diode connecting in reverse bias negative terminal of a source is connected to the anode (A) and positive terminal of the source is connected to cathode (K). Given applied voltage are low small leakage current flows is zener effect. Voltage is increased zener conduct as Avalanche breakdown attain to starts current flowing in the circuit.

Types of breakdown

Zener breakdown
Avalanche breakdown

Zener breakdown occur on minimum leakage current flow through cathode to anode in reverse bias is noted Vz.

Avalanche breakdown occur on conduction stage to break depletion region current flow occur in reverse bias.

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V-I Characteristic of Zener

First quadrant shown a positive graph of forward bias of zener diode it same as like a diode .

Third quadrant shown a negative graph of reverse bias of zener diode. The breakdown occurs due to minority carriers in minimum current flow this is zener effect.

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Breakdown Zener voltage – Vz

Minimum current of zener – Iz min

Maximum current of zener – Iz max

Merits of Zener

Power dissipation of capacity is maximum.
Installed in both forward and reverse bias.
Connection in both series and shunt function.
Follow Output voltage as constant function.

Demerits of Zener

Zener not used in power electronics circuit.
Voltage regulation difference is poor.
In circuit internal impedance is maximum.
Zener resistance changes the output voltage.

Applications of Zener

voltage regulator in circuits.
wave shaping circuits.
transistor biasing circuits as reference voltage.
protection against over voltage.
fixed reference of calibrating voltmeters

Voltage Reference as Zener

Zener diode connected series with load resistance. zener supply constant voltage reference to load. By varying the zener rating depends on input voltage.

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V_R = I * R

I = Io + Iz

R = Vs – Vr / Iz + Io

Here V_R= voltage across the resistor

V_s = input voltage

V_Z = zener voltage

I_Z= break down current or current through zener

R= V_s – V_R / I_Z+ I_out

I_out= current driven to the reference input

Voltage Regular as Zener

The zener diode is connecting shunt to load register because the zener voltage maintain equal to output voltage. Applied voltage regulated by zener voltage drop across load. supply current (I_s) is split into zener current (I_Z) and load current (I_L).

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V_R = V_S – V_Z

V_S – V_{Z =}(I_Z+I_L) * R

Transistor Series as Zener

Emitter follow configuration with base voltage fixed as transistor series voltage regulator. zener diode connecting series in base line to maintain the constant voltage to base. Since the output current I_L is same to the base current I_B(I_B = I_L)

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the I_B is equal to voltage of diode V_Z, whatever each time the applied voltage any change to the input voltage.

I_B+I_L= I_E= I_L

I_L = V_out/R

V_out = (V_Z –V_BE)

I_L= (V_Z –V_BE)/ R = P/ V_out

at P- load power rating

I_{L =}I_Bβ+I_B

I_B= I_L / (1+β)

Β = amplification factor

V_s – V_Z=(I_B+ I_Z) R

R = V_S – V_Z/ (I_B+ I_Z)

V_out = V_Z – V_BE

Op-amp circuit using Zener

Zener diode used in transistor circuit as voltage regulator connected series to positive line. Circuit consist of non inverting amplifier as reference voltage fixed. so the current through the R1 is equal to I_Z zener current. Adjust output voltage by varying the value of resistance R2 and R3 as required.

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V_out= [ (R₂+R₃) / R₃] V_Z

= [1+R₂/ R₃] V_Z

Zener vS Diode