1410040957.1064-Chapter 2 Zener Diode

transcript

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.

1410040957.1064-Chapter 2 Zener Diode

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