Modern Component Families and Circuit Block Design

Nihal Kularatna

• Publisher: Newnes
• Year: 2000
• Print ISBN: 9780750699921
• eBook ISBN: 9780080511962
• Topic: Technik & Maschinenbau
• Subtopic: Industriedesign

Kularatna's new book describes modern component families and how to design circuit blocks using them. While much of this information may be available elsewhere, in Modern Component Families and Circuit Block Design it is integrated with additional design hints that are unique. The discussion covers most components necessary in an embedded design or a DSP-based real time system design. The chapter on modern semi-conductor sensors allows system designers to use the latest sensor ICs for real-world physical parameter sensing.- Covers the most recent low-power components- Written by an authority on power electronics*Includes extensive illustrations and references

Chapter 1

Voltage References and Voltage Regulators

Dileeka Dia

1.1 Introduction

Almost all electronic systems utilize a regulated power supply as an essential requirement. Most systems need a precision voltage reference as well. In the past, the task of voltage regulation was tediously accomplished with discrete devices. Today, with integrated circuit voltage references and regulators, this task has been significantly simplified. Not only can an extremely high precision be obtained, but also an extremely high degree of temperature stability.

The performance of today’s electronic devices such as microprocessors, test and measuring instruments, and sophisticated portable and handheld equipment is directly related to the quality of the supply voltage. This results in the need for tight regulation, low noise, and excellent transient response. The designer now has a wide choice of fixed, adjustable, and tracking voltage regulators, with many also incorporating built-in protection features.

One of the fastest growing markets in the world of power regulation is for switching regulators. These offer designers several important advantages over linear regulators, the most significant being size and efficiency. In addition, the ability to perform step-up, step-down, or voltage inverting functions is an attractive feature.

The old linear regulator is not totally out of business. The proliferation of battery-powered equipment in recent years has accelerated the development and usage of low-dropout (LDO) voltage regulators. Compared to a standard linear regulator, the LDO regulator using PNP transistors can maintain its output in regulation with a much lower voltage across it. While the NPN transistor requires about 2 V of headroom voltage to regulate, the LDO typically will work with less than 500 mV of input-to-output voltage differential. This reduced input voltage requirement is advantageous in battery-powered systems, since it translates directly into fewer battery cells (Simpson, 1996). In low-dropout applications, the efficiency advantage of switching regulators no longer is as great. A linear regulator design on the other hand offers several desirable features, such as low output noise and wide bandwidth, resulting in excellent transient response.

This chapter describes the basics of voltage references, linear and switching regulators, and continues to discuss the state-of-the-art components available, the advantages and disadvantages of different types of devices, their application environments as well as the basics of regulator design using these components.

1.2 Voltage References

1.2.1 Voltage Reference Fundamentals

A wide variety of voltage references are available today. However, all base their performance on the action of either a zener diode or a bandgap cell. Additional circuitry is included to obtain good temperature stability. Although discrete zener diodes are available in voltage ratings as low as 1.8 V to as high as 200 V, with power handling capabilities in excess of 100 W, their tolerance and temperature characteristics are unsuitable for many applications. Therefore, discrete zener diode-based references have additional circuitry to improve performance. The most popular reference is probably the temperature-compensated zener diode, particularly, for voltages above 5 V.

The operation of a bandgap reference is based on specific characteristics of diodes operating at the same current but different current densities. Bandgap references are available with output voltage ratings of about 1.2 to 10 V. The principal advantage of these devices is their ability to provide stable low voltages, such as 1.2, 2.5, or 5 V. However, bandgap references of 5 V and higher tend to have more noise than equivalent zener-based references. This is because, in bandgap references, higher voltages are obtained by amplification of the 1.2 V bandgap voltage by an internal amplifier. Their temperature stability also is below that of zener-based references.

1.2.2 Types of Voltage References

1.2.2.1 Zener-Based Voltage References

Zener diodes are semiconductor PN junction diodes with controlled reverse-bias properties, which make them extremely useful as voltage references. The V-I characteristics of an ideal zener diode is shown in Figure 1–1 (a) and a simple regulator circuit based on it in Figure 1-1 (b).

Figure 1-1 Zener diode and voltage regulator (a) Typical zener characteristics (b) a simple zener diode voltage regulator

The reverse characteristics show that, at the breakdown point, the knee voltage is independent of the diode current. This knee voltage or the zener voltage is controlled by the amount of doping applied in the manufacturing process. In the simple regulator circuit shown in Figure 1–1 (b), as long as the zener diode is in its regulating range, the load voltage V_L remains constant and equal to the nominal zener voltage, even when the input voltage and the load resistance varies over a wide range. If the input voltage increases, the diode maintains a constant voltage across the load by absorbing the extra current and keeping the load current constant. If the load resistance decreases, the extra current required to keep the load voltage constant is facilitated by a decrease in the current drawn by the zener diode.

In the preceding simplified analysis, the temperatu...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Dedication
• Preface
• Acknowledgments
• Chapter 1: Voltage References and Voltage Regulators
• Chapter 2: Operational Amplifiers
• Chapter 3: Data Converters
• Chapter 4: Microprocessors and Microcontrollers
• Chapter 5: Digital Signal Processors
• Chapter 6: Optoisolators
• Chapter 7: Sensors
• Chapter 8: Nonlinear Devices
• Chapter 9: Rechargeable Batteries and Their Management
• Chapter 10: Programmable Logic Devices
• Index