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

Forward- and reverse-biased pn junctions Figure 9.7

Semiconductor diode i-v characteristic Semiconductor diode circuit symbol Figure 9.8, 9.9

The i-v characteristic of the semiconductor diode Figure 9.10

Shockley Equation 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 a temperature of 300 K, we have

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.

LOAD-LINE ANASYSIS OF DIODE CIRCUITS

LOAD-LINE ANALYSIS OF DIODE CIRCUITS By applying KVL, we get But two unknowns, we need one more equation relating iD and vD to solve the problem.

Example 10. 1 If the circuit of Figure 10 Example 10.1 If the circuit of Figure 10.5 has Vss = 2V, R = 1kW, and a diode with the characteristic shown in Figure 10.7, find the diode voltage and current at the operating point. Example 10.2 Repeat Example 10.1 if Vss = 10V, R = 10kW

Vss = i R + VD Vss = 2, R = 1k Vss=10, R=10k

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

Example 10. 3 The voltage-regulator circuit of Figure 10 Example 10.3 The voltage-regulator circuit of Figure 10.9 has R = 1kW 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 = 0 i = 0, VD = -Vss VD = 0, i = Vss/R

IDEAL-DIODE MODEL

IDEAL-DIODE MODEL The ideal diode acts as a short circuit for forward currents and as an open circuit with reverse voltage applied.

Large-signal on/off diode model Figure 9.11

Circuit containing ideal diode Circuit of Figure 9.12, assuming that the ideal diode conducts Figure 9.13 Figure 9.12, 9.13, 9.14 Circuit of Figure 9.12, assuming that the ideal diode does not conduct Figure 9.14

Figure 9.16 Figure 9.15, 9.16, 9.17 Figure 9.17

Summary of Guidelines to analysis ideal-diode circuits

APPLICATION OF DIODES

DC power supply Figure 9.45

RECTIFIER CIRCUITS

Half-Wave Rectifier Circuits

Ideal diode rectifier input and output voltages Figure 9.20, 9.21

As Vs reaches VB, then diode starts to conduct

Full-Wave Rectifier Circuits

Full-wave rectifier

Operation of bridge rectifier Figure 9.42

A Zener diode voltage regulator; (b) simplified circuit for Zener regulator Figure 9.49