Eeng 3510 chapter 3
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EENG 3510 Chapter 3. Diodes. Chapter 3 Homework. 3.2 (c & d), 3.3 , 3.9, 3.19, 3.23 . 3.1.1 Current-Voltage Characteristic. diode circuit symbol. i – v characteristic. equivalent circuit in the forward direction. equivalent circuit in the reverse direction.

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EENG 3510 Chapter 3

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Eeng 3510 chapter 3

EENG 3510 Chapter 3

Diodes


Chapter 3 homework

Chapter 3 Homework

3.2 (c & d), 3.3 , 3.9, 3.19, 3.23


3 1 1 current voltage characteristic

3.1.1 Current-Voltage Characteristic

diode circuit symbol

i–vcharacteristic

equivalent circuit in the forward direction

equivalent circuit in the reverse direction


3 1 1 current voltage characteristic1

3.1.1 Current-Voltage Characteristic

an external circuit to limit the forward current

the reverse voltage


3 1 2 a simple application the rectifier

3.1.2 A Simple Application: The Rectifier


3 1 3 another application diode logic gates in a positive logic system

3.1.3 Another Application: Diode Logic Gates(In a positive-logic system)

AND gate (in a positive-logic system)

OR gate


Example 3 2 find values of i and v

Example 3.2 Find values of I and V


Example 3 2a find values of i and v

Example 3.2a Find values of I and V

1. Both diodes are conducting.

Voltage at B is zero.

ID2 = 10 V -0 V / 10 k = 1 mA

I + ID2 = (0 – (-10) V ) / 5 k = 2 mA

I + 1 = 2mA

I = 1 mA

5.V = 0


Example 3 2b find values of i and v

Example 3.2b Find values of I and V

  • Assume both diodes are conducting.

  • VB = 0

  • ID2 = (10 V – 0 V) / 5k = 2 mA

  • I + 2 = (0 – (-10)) V / 10 k

  • I = - 1 A This is not correct.

  • Assume D1 is off and D2 is on.

  • ID2 = (10 V – (-10 V) )/ 15k = 1.33 mA

  • V = VB = -10 V + (10 k X 1.33 mA)

  • V = -10 V + 13.3 V = 3.3 V


Exercise 3 4a find i v

Exercise 3.4a - Find: I & V

I = 5 V / 2.5 K = 2 mA

V = 0, Why ?

V


Exercise 3 4b find i v

Exercise 3.4b - Find: I & V

I = 0 A, Why?

V

V = 5 V, Why ?


Exercise 3 4c find i v

Exercise 3.4c - Find: I & V

V

I = 0 A, Why?

V = 5 V, Why ?


Exercise 3 4d find i v

Exercise 3.4d - Find: I & V

V

I = 5 V / 2.5 K = 2 mA

V = 0, Why ?


Exercise 3 4e find i v

Exercise 3.4e - Find: I & V

I = 3 V / 1 K = 3mA

V = 3 V, Why ?


Exercise 3 4f find i v

Exercise 3.4f - Find: I & V

I = 4 V / 1 K = 4mA

V = 1 V, Why ?


3 2 terminal characteristics of junction diodes

3.2 Terminal Characteristics of Junction Diodes


3 2 terminal characteristics of junction diodes1

3.2 Terminal Characteristics of Junction Diodes


3 2 1 the forward bias region

3.2.1 The Forward-Bias Region

V = forward voltage


3 2 1 the forward bias region cont

3.2.1 The Forward-Bias Region (cont.)

Silicon diodes conduct when the forward voltage = 0.7 volts

Germanium diodes conduct when the forward voltage = 0.3volts


Example

Example

Given: A forward biased diode, forward voltage drop is 0.7 V at 2 mA,

n = 1 at 0.6 V

Find : the current i2


3 2 2 the reverse bias region

3.2.2 The Reverse-Bias Region


3 2 3 the breakdown region

3.2.3 The Breakdown Region


3 3 modeling the diode forward characteristics 3 3 1 the exponential model

3.3 Modeling the Diode Forward Characteristics3.3.1 The Exponential Model

Graphical Analysis


3 3 modeling the diode forward characteristics 3 3 3 iterative analysis using theexponential model

3.3 Modeling the Diode Forward Characteristics3.3.3 Iterative Analysis Using theExponential Model


3 3 modeling the diode forward characteristics 3 3 5 the piecewise linear model

3.3 Modeling the Diode Forward Characteristics3.3.5 The Piecewise-Linear Model


3 3 modeling the diode forward characteristics 3 3 5 the piecewise linear model cont

3.3 Modeling the Diode Forward Characteristics3.3.5 The Piecewise-Linear Model (cont.)

Piecewise-linear model of the diode forward characteristic and its equivalent circuit representation


3 3 modeling the diode forward characteristics 3 3 6 the constant voltage drop model

3.3 Modeling the Diode Forward Characteristics3.3.6 The Constant-Voltage-Drop Model

Development of the constant-voltage-drop model of the diode forward characteristics. A vertical straight line (B) is used to approximate the fast-rising exponential. Observe that this simple model predicts VD to within 0.1 V over the current range of 0.1 mA to 10 mA.


3 3 modeling the diode forward characteristics 3 3 6 the constant voltage drop model1

3.3 Modeling the Diode Forward Characteristics3.3.6 The Constant-Voltage-Drop Model

The constant-voltage-drop model of the diode forward characteristics and its equivalent-circuit representation.


Eeng 3510 chapter 3

3.3 Modeling the Diode Forward Characteristics 3.3.9 Use of the Diode Forward Drop in Voltage Regulation

  • A voltage regulator is a circuit whose purpose is to provide a constant dc voltage between its output terminals

  • The output voltage is required to remain as constant as possible in spite of

    • Changes in the load current drawn from the regulator output terminal

    • Changes in the dc power-supply voltage that feeds the regulator circuit


Eeng 3510 chapter 3

3.3 Modeling the Diode Forward Characteristics 3.3.9 Use of the Diode Forward Drop in Voltage Regulation


Eeng 3510 chapter 3

3.4 Operation in the Reverse Breakdown Region –Zener Diodes3.4.1 Specifying and Modeling the Zener Diode

Circuit symbol for a zener diode.


3 4 operation in the reverse breakdown region zener diodes 3 4 4 a final remark

3.4 Operation in the Reverse Breakdown Region –Zener Diodes3.4.4 A Final Remark

  • In recent years, zener diodes are replaced in voltage-regulator design by specially designed integrated circuits (ICs) that perform the voltage regulation function much more effectively and with greater flexibility than zener diodes.


3 5 rectifier circuits

3.5 Rectifier Circuits

120(N2/N1) V

Coils wound

around an iron core

Remove pulsation

Remove ripple


3 5 1 the half wave rectifier

3.5.1 The Half-Wave Rectifier

Half-wave rectifier

Transfer characteristic of the rectifier circuit

Equivalent circuit of the half-wave rectifier with the diode replaced with its battery-plus-resistance model.

Input and output waveforms, assuming that rD!R.


3 5 1 the half wave rectifier cont

3.5.1 The Half-Wave Rectifier (cont.)

  • Two important parameters:

    1) Current-handling capability: the largest current the diode

    is expected to conduct

    2) Peak inverse voltage (PIV): the diode must be able to

    withstand without break


3 5 2 the full wave rectifier

3.5.2 The Full-Wave Rectifier

Full-wave rectifier utilizing a transformer with a center-tapped secondary winding

transfer characteristic assuming a constant-voltage-drop model for the diodes;

input and output waveforms


3 5 3 the bridge rectifier

3.5.3 The Bridge Rectifier

Most Popular Rectifier Circuit Configuration

The bridge rectifier

input and output waveforms


3 5 4 the rectifier with a filter capacitor the peak rectifier

3.5.4 The Rectifier with a Filter Capacitor The Peak Rectifier

A simple circuit used to illustrate the effect of a filter capacitor.

Note that the circuit provides a dc voltage equal to the peak of the input sine wave. The circuit is therefore known as a peak rectifier or a peak detector.

Input and output waveforms assuming an ideal diode.


3 5 4 the rectifier with a filter capacitor the peak rectifier1

3.5.4 The Rectifier with a Filter Capacitor The Peak Rectifier


3 5 4 the rectifier with a filter capacitor the peak rectifier2

3.5.4 The Rectifier with a Filter Capacitor The Peak Rectifier

Waveforms in the full-wave peak rectifier


3 7 1 basic semiconductor concepts

3.7.1 Basic Semiconductor Concepts

Simplified physical structure of the junction diode.

(Actual geometries are given in Appendix A.)


3 7 1 basic semiconductor concepts cont

3.7.1 Basic Semiconductor Concepts (cont.)

Two-dimensional representation of the silicon crystal. The circles represent the inner core of silicon atoms, with +4 indicating its positive charge of +4q, which is neutralized by the charge of the four valence electrons. Observe how the covalent bonds are formed by sharing of the valence electrons. At 0 K, all bonds are intact and no free electrons are available for current conduction.


3 7 1 basic semiconductor concepts cont1

3.7.1 Basic Semiconductor Concepts (cont.)

At room temperature, some of the covalent bonds are broken by thermal ionization. Each broken bond gives rise to a free electron and a hole, both of which become available for current conduction.


3 7 1 basic semiconductor concepts cont2

3.7.1 Basic Semiconductor Concepts (cont.)

The concentration of free electrons n, and the concentration of holes p


3 7 1 basic semiconductor concepts cont3

3.7.1 Basic Semiconductor Concepts (cont.)


3 7 1 basic semiconductor concepts cont4

3.7.1 Basic Semiconductor Concepts (cont.)

Ex: phosphorus

A silicon crystal doped by a pentavalent element. Each dopant atom donates a free electron and is thus called a donor. The doped semiconductor becomes n type.


3 7 1 basic semiconductor concepts cont5

3.7.1 Basic Semiconductor Concepts (cont.)

Ex: boron

A silicon crystal doped with a trivalent impurity. Each dopant atom gives rise to a hole, and the semiconductor becomes p type.


3 7 2 the pn junction under open circuit conditions

3.7.2 The pn Junction Under Open-Circuit Conditions

Equilibium: Is= ID,

Maintained by the barrier voltage V0

(a) The pn junction with no applied voltage (open-circuited terminals). (b) The potential distribution along an axis perpendicular to the junction.


3 7 2 the pn junction under open circuit conditions1

3.7.2 The pn Junction Under Open-Circuit Conditions


3 7 2 the pn junction under open circuit conditions2

3.7.2 The pn Junction Under Open-Circuit Conditions


3 7 3 the pn junction under reverse bias conditions

3.7.3 The pn Junction Under Reverse-Bias Conditions

Anode

Cathode

Depletion width: increases

Barrier voltage v0: increase

I = IS-ID

The pn junction excited by a constant-current source I in the reverse direction. To avoid breakdown, I is kept smaller than IS.Note that the depletion layer widens and the barrier voltage increases by VRvolts, which appears between the terminals as a reverse voltage.


3 7 3 the pn junction under reverse bias conditions1

3.7.3 The pn Junction Under Reverse-Bias Conditions

Anode

Cathode

Depletion width: decrease

Barrier voltage v0: decrease

I = ID -IS

The pnjunction excited by a constant-current source supplying a current I in the forward direction. The depletion layer narrows and the barrier voltage decreases by V volts, which appears as an external voltage in the forward direction.


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