1410040957.1064-Chapter 2 Zener Diode

8/10/2019 1410040957.1064-Chapter 2 Zener Diode

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Chapter 2ZENER DIODE


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Zener diodesThe breakdown characteristics of diodes can

be tailored by controlling the dopingconcentration

Heavily doped p+and n-regions result in low

breakdown voltage (Zener effect)

Used as reference voltage in voltage

regulators I

VRegion of

operation

Region of

operation

Region of

operation


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ZENER DIODE


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Basic Zener regulator

Viand RLFixed

L

il

L

RR

VRVV

If VV

ZandIz >Izmin that means the Zener diode is on

If V


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Basic zener regulator

Vi and RLFixed

LZR III

ZZZ IVP

LRZ III

2. Substitute the appropriate equivalent circuit

and solve for the desired unknowns.ZL VV

L

LL

R

VI

R

VVI

LiR


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Fixed Vi, Variable RL

min maxL R ZI I I

Zi

Z

L

VVRVR

min

minmax

L

ZL

I

VR

R

VI

RR

min

max

Z

L

L

VR

I

ziR VVV

OR: If Izminis given:

Z R LI I I

max minL R ZI I I

Using VDR

2- Finding RLmax:

1- Finding RLmin:


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AC Limiter

Applications

Protection circuit


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Half Wave Voltage Doubler

High Voltage transformers are expensive andimpractical at voltages above 1000V

The peak inverse voltage PIV across each diode is 2Vp


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Half Wave Voltage Doubler

First Half Cycle D1conducting, C1

charged. C2remains uncharged

because of the reverse biased D2

Second Half Cycle D2conducting, C2

charged by (source + C1) about

twice the source voltage

Next HalfCycle Repeat of first stage

with the addition that C2can now

discharge through RL. Notice that C2

is charged once/cycle, so output has

the same frequency as input.


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Full Wave Voltage Doubler

When the secondary voltage ispositive, D1is forward-biased and C1charges to approximately Vp

During the negative half-cycle, D2isforward-biased and C 2charges to

approximately Vp. The outputvoltage 2Vp- is taken across the twocapacitors in series.

The peak inverse voltage PIV across each diode is 2Vp


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Voltage Tripler

The addition of another diode-capacitor section to the half-wavevoltage doubler creates a voltage tripler. The operation is as

follows: On the positive half-cycle of the secondary voltage. C 1

charges to Vp, through D1. During the negative half-cycle,

C 2 charges to 2Vp through D2 as described for the doubler. Duringthe next positive half-cycle, C 3 charges to 2Vp through D3 the

tripler output is taken across C 1 and C 3.


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Voltage Quadrupler

The addition of still another diode-capacitor section produces an output four

times the peak secondary voltage. C4charges to 2Vp through D4on a

negative half-cycle. The 4V p output is taken across C2and C4, as shown.

In both the tripler and quadrupler circuits. the PlV of each diode is 2Vp


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Voltage Quadrupler

Can extend this circuit to produce

extremelyhigh voltages (~750kV).

Voltage Quadrupler


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Special Purpose Diodes


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Varactor Diodes

A varactor diodeis best explained as a variable capacitor. Think of the depletion region a

variable dielectric. The diode is placed in reverse bias. The dielectric is adjusted by bias

changes.


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Varactor Diodes

The varactor diode can be useful in filter circuits as theadjustable component.


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Other Diode Types

The Schottky diodessignificant characteristic is its fast switching speed. This is useful forhigh frequencies and digital applications. It is not a typical diode in the fact that it does not

have a p-n junction, instead it consists of a heavily doped n-material and metal bound

together.


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Other Diode Types

ThePIN

diodeis also used in mostly microwave frequency applications. Its variable forwardseries resistance characteristic is used for attenuation, modulation, and switching. In reverse

bias exhibits a nearly constant capacitance.


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Other Diode Types

The tunnel diodeis also used for fast switching applications.

This is achieved by reduced doping at the junction.


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Other Diode Types

The laser diode(light amplification by stimulated emission ofradiation) produces amonochromatic (single color) light. Laser diodes in conjunction with photodiodes are used

to retrieve data from compact discs.

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1410040957.1064-Chapter 2 Zener Diode

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