Diodes

1. Basic diode concept.

2. Load-line analysis of diode circuit.

3. Zener-diode voltage regulator circuit.

4. Ideal-diode model.

5. Applications of diodes.

BASIC DIODE CONCEPTS

A pn junction

Drift and diffusion currents in a pn junction

Figure 9.7

Forward- and reverse-biased pn junctions

Figure 9.8, 9.9

Semiconductor diode i-v characteristic

Semiconductor diode circuit symbol

Figure 9.10

The i-v characteristic of the semiconductor diode

Shockley Equation

1exp

T

DsD nV

vIi

q

kTVT

k = 1.38 × 10–23 J/K is Boltzmann’s constant and q = 1.60 × 10–19 C is the magnitude of the electrical charge of an electron. At atemperature of 300 K, we have mV 26TV

Exercise 10.1

At a temperature of 300K, a certain junction

diode has iD = 0.1mA for vD = 0.6V. Assume

that n is unity and use VT = 0.026V. find the

value of the saturation current Is.

1exp

T

DsD nV

vIi

A

nVv

iIs

TD

D

15

4

10502.9

1)026.0/6.0exp(10

1)/exp(

LOAD-LINE ANASYSIS OF DIODE CIRCUITS

LOAD-LINE ANALYSIS OF DIODE CIRCUITS

DDSS vRiV By applying KVL, we get

But two unknowns, we need one more equation relating iD and vD to solve the problem.

Example 10.1If the circuit of Figure 10.5 has Vss = 2V,

R = 1k, and a diode with the characteristic shown in Figure 10.7, find the diode voltage and current at the operating point.

Example 10.2Repeat Example 10.1 if Vss = 10V, R = 10k

Vss=10, R=10k

Vss = 2, R = 1k

Vss = i R + VD

ZENER-DIODE VOLTAGE-REGULATOR CIRCUITS

What is a Zener diode?

Zener Diodes

Diodes that are intended to operate in the breakdown region are called Zener diodes.

Breakdown

region

ZENER-DIODE VOLTAGE-REGULATOR

CIRCUITSA voltage regulator circuit provides a nearly constant voltage to a load from a variable source.

0 DDSS vRiV

Example 10.3

The voltage-regulator circuit of Figure 10.9

has R = 1k and use a Zener diode having the

characteristic shown in Figure 10.10. Find the

output voltage for Vss = 15V. Repeat for Vss =

20V.

R = 1k

Vss + i R +VD = 0i = 0, VD = -Vss

VD = 0, i = Vss/R

IDEAL-DIODE MODEL

IDEAL-DIODE MODEL

The ideal diode acts as a shortcircuit for forward currentsand as an open circuit withreverse voltage applied.

Figure 9.11

Large-signal on/off diode model

Figure 9.12, 9.13, 9.14

Circuit containing ideal diode Circuit of Figure 9.12, assuming that the ideal diode conducts

Figure 9.13

Circuit of Figure 9.12, assuming that the ideal diode does not conduct

Figure 9.14

Figure 9.15, 9.16, 9.17

Figure 9.17

Figure 9.16

Summary of Guidelines to analysis ideal-diode

circuits

APPLICATION OF DIODES

Figure 9.45

DC power supply

RECTIFIER CIRCUITS

Half-Wave Rectifier Circuits

Figure 9.20, 9.21

Ideal diode rectifier input and output voltages

As Vs reaches VB, then diode starts to conduct

r

L

V

TIC

2r

mL

VVV

Vr/ 2

Full-Wave Rectifier Circuits

Full-wave rectifier

Figure 9.42

Operation of bridge rectifier

Figure 9.49

(a) A Zener diode voltage regulator;

(b) (b) simplified circuit for Zener regulator