Prepared by: Kenneth Joachim Llanto

Last Updated: 06/21/11

◦ Construction and operation, characteristic curve

◦ Diode Equivalent Model

◦ Diode Circuit Analysis

◦ Light Emitting Diode

◦ Zener Diode

Some electrons will cross

the junction and fill holes

A pair of ions is created

each time this happens

As this ion charge builds up, it prevents

further charge migration across the junction

Depletion layer

These ions create a potential

Difference called barrier potential

Silicon = 0.7 V; Germanium = 0.3 V

GaAs = 1.2 V

Reverse-Bias Condition (VD < 0 V)

- +

- +

This results to

a wider

depletion region

Reverse-Bias Condition (VD < 0 V)

Forward-Bias Condition (VD > 0 V)

-+

+ -

Carriers diffuse through depletion

region and across the

junction, producing current

Silicon = 0.7 V;

Germanium = 0.3 V

GaAs = 1.2 V

Forward-Bias Condition (VD > 0 V)

A characteristic curve defines the operatingconditions of a device from several inputparameters that provide a given output value.

It is a plot of the input/output relationships ofa device.

The Diode Starts to

conduct when the

barrier voltage is reached

leakage current

The diode conducts once the

Breakdown voltage is exceeded

Breakdown Voltage◦ Voltage that causes Avalanche, reverse voltage

becomes too excessive causing the free electrons on the p side to be accelerated

Leakage Current◦ A small reverse current exists at reverse bias

brought about by the minority carriers.

◦ Increases with temperature

This represents the diode as being ideal.

The first approximation ignores :◦ leakage current

◦ barrier potential

◦ bulk resistance.

When an ideal diode

is forward biased, the

model is a closed switch.

When an ideal diode is

reverse biased, the

model is an open switch

Reverse bias

Forward bias

This model assumes that no diode current flows until the forward bias across the diode reaches 0.7 volts (For Si).

This model ignores :◦ exact shape of the knee.

◦ bulk resistance.

0.7 V

Reverse bias

0.7 V

Forward bias

This model assumes that no diode current flows until the forward bias across the diode reaches 0.7 volts (for Si).

This model ignores :◦ exact shape of the knee.

RB

0.7 V

Reverse bias

RB

0.7 V

Forward bias

RB = △ V / △I

A silicon diode has a forward voltage drop of 2.0 v for a forward diode with

Current of 1.5 A. Calculate the RB

RB

2.0 – 0.7

1.5 – 0.0 1.5

1.3== 0.867 ohms=

Solve for the load voltage and current using first, second and third approximations. Use Si diode RB = 3.1 ohms

RL = 220 ohmsVIN = 18 V

RB = 2.5 ohms

RL = 1000 ohmsVIN = 25 V

Solve for the load voltage and current using first, second and third approximations. Use Si diode

RB = 3.1 ohms

RL = 220 ohmsVIN = 18 V

1st Approx: VL = 18 V , IL = 81 mA

2nd Approx: VL = 17.3 V , IL = 78.6 mA

3rd Approx: VL = 17.1 V , IL = 77.5 mA

Solve for the load voltage and current using first, second and third approximations. Use Si diode

RB = 2.5 ohms

RL = 1000 ohmsVIN = 25 V

1st Approx: VL = 25 V , IL = 25 mA

2nd Approx: VL = 24.3 V , IL = 24.3 mA

3rd Approx: VL = 24.2 V , IL = 24.2 mA

Solve for the load voltage and current using first, second and third approximations. Use Si diode

Lecture notes by Engr. Emmanuel Guevara

Lecture notes by Engr. Angelo dela Cruz

Electronic Devices and Circuit Theory by Boylestad and Nashelsky

Grob’s Basic Electronics by Schultz

Electronic Principles by Malvino and Bates