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PARUL INSTITUTE OF ENGINEERING & TECHNOLOGY

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Introduction

The basic function of zener diodeis to maintain a specificvoltage across its terminals within given limits of line orload change. Typically it is used for providing a stablereference voltage for use in power supplies and otherequipment.

This particular zener circuit will work to maintain 10 V across the load.

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Zener Diodes

A zener diodeis muchlike a normal diode, theexception being is that it isplaced in the circuit inreverse bias and operatesin reverse breakdown.This typical characteristiccurve illustrates theoperating range for a

zener. Note that itsforward characteristics arejust like a normal diode.

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The zener diodesbreakdown characteristicsare determined by thedoping process. Lowvoltage zeners less than

5V operate in the zenerbreakdown range. Thosedesigned to operate morethan 5 V operate mostlyin avalanche breakdown

range. Zeners areavailable with voltagebreakdowns of 1.8 V to200 V.

Zz=

This curve illustrates the minimum andmaximum ranges of current operation that thezener can effectively maintain its voltage.IzVz

/

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Zener Diodes Characteristics

Exmaple: What is the voltage across the zener IN4736terminals when the current is 50 mA? When the currentis 25 mA? (Check the table in page 116)

Temperature Coefficient

Power Dissipation PD= VzIz

Power Derating PD(derated) = PD(max)

C)%/:(TCV TTCVzz

C)V/:(TCV TTCz

C)T(mW/

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Zener Diodes

As with most devices, zener diodes have given

characteristics such as temperature coefficients andpower ratings that have to be considered.

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Zener Diode ApplicationsRegulation

In this simple illustration of zener regulation circuit, the zenerdiode will adjust its impedance based on varying inputvoltages and loads (RL) to be able to maintain its designatedzener voltage. Zener current will increase or decrease directlywith voltage input changes. The zener current will increase ordecrease inversely with varying loads. Again, the zener has afinite range of operation.

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Zener Diode ApplicationRegulator

Minimum and maximum input voltage of

IN4733

No load, Full load of zener regulator

Example 3-6

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Zener Limiting

Zener diodes can used for limiting just as normal diodes.Recall in previous chapter studies about limiters. Thedifference to consider for a zener limiter is its zenerbreakdown characteristics.

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Summary

The zener diode operates in reverse breakdown.

A zener diode maintains a nearly constant voltageacross its terminals over a specified range of currents.

Line regulation is the maintenance of a specificvoltage with changing input voltages.

Load regulation is the maintenance of a specificvoltage for different loads.

There are other diode types used for specific RF

purposes such as varactor diodes (variablecapacitance), Schottky diodes (high speed switching),and PIN diodes (microwave attenuation andswitching).