Physics
Ideal Diode
An ideal diode is a theoretical electronic component that only allows current to flow in one direction, offering zero resistance in the forward direction and infinite resistance in the reverse direction. It is often used as a simplified model for analyzing and designing electronic circuits. In practical applications, real diodes exhibit some non-ideal characteristics such as voltage drops and finite reverse resistance.
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eBook - PDFElectronic Concepts
An Introduction
- Jerrold H. Krenz(Author)
- 2000(Publication Date)
- Cambridge University Press(Publisher)
In addition, the design of diode circuits relies on one's ability to conceptualize the behavior of diodes. THE Ideal Diode SWITCH MODEL An approximate diode model, suitable for some applications, is that of a circuit element generally referred to as an Ideal Diode. It has the idealized characteristic of Figure 2.37. The voltage across an Ideal Diode, when it is forward biased (*D > 0), is zero, and its current, when reverse biased (VE> < 0), is zero. This model can be used to replace an actual semiconductor diode in a circuit when the voltages of the circuit are large compared with the small forward voltage of an actual diode. Because either the voltage or current of an Ideal Diode is zero, the diode may be treated as the ideal switch of Figure 2.38. The switch is either open, Figure 2.37: Actual and idealized characteristics of a diode. b i b + X i D = J v D = actual diode idealized diode 92 THE SEMICONDUCTOR JUNCTION DIODE D . . D Ideal open switch for v D <0 closed switch for i D > 0 Figure 2.38: Simulating the behavior of an Ideal Diode with a switch. corresponding to a reverse-biased condition, or closed, corresponding to a for-ward-biased condition. The condition of the switch depends on its voltage or cur-rent which, in turn, depends on the other elements of the circuit. It is necessary to make a binary logic decision as to the condition of the switch (decide if it is open or closed). The difficulty is that of ascertaining the correct condition. For some circuits, the choice may be obvious, whereas for others, especially if a circuit has several diodes, the choice may not be so obvious. If the decision is not obvious, it is necessary to guess and proceed using a trial-and-error solution. One solves the circuit for the initial decision; a simple analytic solution is generally possible if there are no other nonlinear elements. If it was assumed that the diode was reverse biased (an open switch), its resultant voltage must be negative.
eBook - PDFFundamentals of Electronics
Book 1 Electronic Devices and Circuit Applications
- Thomas F. Schubert, Ernest M. Kim(Authors)
- 2022(Publication Date)
- Springer(Publisher)
63 C H A P T E R 2 Diode Characteristics and Circuits Simple electronic circuit elements can be divided into two fundamental groups by their terminal characteristics: • Linear devices – devices that can be described by linear algebraic equations or linear differ- ential equations; • Non-linear devices – those devices that are described by non-linear equations. Resistors, capacitors, and inductors are examples of passive circuit elements that are basically lin- ear.¹ Operational amplifiers, when functioning within certain operational constraints (as described in Chapter 1), are linear, active devices. e diode is the most basic of the non-linear electronic circuit elements. It is a simple two-terminal device whose name is derived from the vacuum tube technology device with sim- ilar characteristics: a tube with two electrodes (di - two; ode - path), the anode and the cathode. Vacuum tube devices have largely been superseded in electronic applications by semiconductor junction diodes. is chapter will restrict its discussion to semiconductor diodes, diode charac- teristics, and simple electronic diode applications. 2.1 BASIC FUNCTIONAL REQUIREMENTS OF AN Ideal Diode ere are many applications in electronic circuitry for a one-way device: that is, a device that pro- vides zero resistance to current flowing in one direction, but infinite resistance to current flowing the opposite direction. Protection against misapplied currents or voltages, converting alternating current (AC) into direct current (DC), demodulating Amplitude Modulated (AM) radio signals, and limiting voltages to specified maxima or minima are but a few of the many possible applica- tions. While a device with such ideal characteristics may be impossible to manufacture, its study is still instructive and, in many applications, ideal devices closely approximate real devices and provide insight into real-device circuit operation.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 12 Diode Figure 1: Closeup of a diode, showing the square shaped semiconductor crystal (black object on left) . ____________________ WORLD TECHNOLOGIES ____________________ Figure 2: Various semiconductor diodes. Bottom: A bridge rectifier. In most diodes, a white or black painted band identifies the cathode terminal, that is, the terminal which conventional current flows out of when the diode is conducting. ____________________ WORLD TECHNOLOGIES ____________________ Figure 3: Structure of a vacuum tube diode. The filament may be bare, or more com-monly (as shown here), embedded within and insulated from an enclosing cathode In electronics, a diode is a two-terminal electronic component that conducts electric current in only one direction. The term usually refers to a semiconductor diode , the most common type today. This is a crystalline piece of semiconductor material connected to two electrical terminals. A vacuum tube diode (now little used except in some high-power technologies) is a vacuum tube with two electrodes: a plate and a cathode. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction) while blocking current in the opposite direction (the reverse direction). Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used ____________________ WORLD TECHNOLOGIES ____________________ to convert alternating current to direct current, and to extract modulation from radio signals in radio receivers. However, diodes can have more complicated behavior than this simple on-off action. This is due to their complex non-linear electrical characteristics, which can be tailored by varying the construction of their P-N junction. These are exploited in special purpose diodes that perform many different functions.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- University Publications(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 3 Diode Figure 1: Closeup of a diode, showing the square shaped semiconductor crystal (black object on left) . ____________________ WORLD TECHNOLOGIES ____________________ Figure 2 : Various semiconductor diodes. Bottom: A bridge rectifier . In most diodes, a white or black painted band identifies the cathode terminal, that is, the terminal which conventional current flows out of when the diode is conducting. ____________________ WORLD TECHNOLOGIES ____________________ Figure 3: Structure of a vacuum tube diode. The filament may be bare, or more commonly (as shown here), embedded within and insulated from an enclosing cathode In electronics , a diode is a two-terminal electronic component that conducts electric current in only one direction. The term usually refers to a semiconductor diode , the most common type today. This is a crystalline piece of semiconductor material connected to two electrical terminals. A vacuum tube diode (now little used except in some high-power technologies) is a vacuum tube with two electrodes : a plate and a cathode. The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction) while blocking current in the opposite direction (the reverse direction) . Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification , and is used ____________________ WORLD TECHNOLOGIES ____________________ to convert alternating current to direct current , and to extract modulation from radio signals in radio receivers. However, diodes can have more complicated behavior than this simple on -off action. This is due to their complex non-linear electrical characteristics, which can be tailored by varying the construction of their P-N junction. These are exploited in special purpose diodes that perform many different functions.
eBook - PDFElectronic and Electrical Engineering
Principles and Practice
- Lionel Warnes(Author)
- 2017(Publication Date)
- Red Globe Press(Publisher)
1 The departure of the current-voltage relationship from Equation 7.1 can be taken care of with an ideality factor, , in the exponent; then I = I s [exp( qV AK / kT ) 1], where 1 2. 137 Figure 7.1 A p-n junction diode and its circuit symbol (7.1) 7 Diodes A DIODE is a two-terminal, passive, non-linear device that can be used to control voltage and current in a circuit. Some diodes are used primarily to rectify alternating current, some are used as signal detectors and others are used as voltage references or voltage regulators. There are also optical diodes which are used as indicators (light-emitting diodes, or LEDs), signal sources (LEDs and laser diodes) or optical detectors (avalanche photodiodes and PIN diodes). The solar cell is a special type of optical diode which converts light energy directly into electricity and by tonnage is probably the most important use of diodes today. The shape of a diode’s current-voltage relationship determines its specific application, which in today’s solid-state devices depends on the way it is doped during manufacture. There are several classes of diode besides the ‘ordinary’ rectifier, but of these we shall examine only Schottky diodes, Zener diodes and light-emitting diodes. Optical signal source and detector diodes are discussed in Chapter 25. 7.1 Junction diodes Junction diodes depend on p-n junctions in semiconductors for their operation. They are primarily used for rectification and signal detection, though they can also be used for voltage limitation or regulation. The symbol for an ‘ordinary’ diode is shown in Figure 7.1. The n-type side of the p-n junction is the called the cathode (marked on the device often by a coloured band) and the p-type side is the anode . Forward current is said to flow when the direction of positive (conventional) current flow is from anode to cathode.
eBook - PDF- Marc Thompson(Author)
- 2006(Publication Date)
- Newnes(Publisher)
43 CHAPTER 3 Review of Diode Physics and the Ideal (and Later, Nonideal) Diode Current Flow in Insulators, Good Conductors and Semiconductors In nature, from the point of view of the ease of producing current flow in a material, there are three broad classes of materials: insulators, conductors and semiconductors. Semiconductors and metals can support significant current flow but the charge movement mechanisms are dif-ferent in the two types of materials. How “good” an electrical conductor is can be quantified by material property electrical resistivity and/or its inverse, electrical conductivity. Electrical resistivity 2 is a measure of how well a given material conducts current. If there are lots of free charged carriers available, a material is deemed a good conductor. In This Chapter f The basics of bipolar devices are covered, including basic semiconductor physics, 1 the concepts of electron and hole flow in semiconductors, the differences between drift and diffusion flow, generation and recombination, and the effects of semiconductor doping on carrier concentrations. We finish with a discussion of the Ideal Diode, and illustrate how a diode can conduct forward current, but can also block reverse voltage. Detailed mathematical derivations are avoided wherever possible. However, enough mathematical detail is given so that the reader can discern the important scaling laws and functional dependencies of the Ideal Diode. At the end of the chapter we’ll discuss some of the factors that result in nonideal behavior in diodes. We’ll conclude with a discussion of load lines, a useful method for solving for the operating point of circuits with nonlinear devices. The load-line technique will be useful in later chapters in analyzing transistors. 1 W e will not go into the quantum mechanics of semiconductors, which provides the rigorous analyses. The simpler models developed in this chapter hopefully will give insight into the basics of semiconductor operation.
eBook - PDFDiode, Transistor & Fet Circuits Manual
Newnes Circuits Manual Series
- R. M. Marston(Author)
- 2013(Publication Date)
- Newnes(Publisher)
1 Basic diode circuits The solid-state diode is the most fundamental element used in modern electronics, and is available in a variety of forms, including those of signal detector, rectifier, zener 'voltage reference' diode, noise-generator diode, varicap 'variable capacitance' diode, light-sensitive diode (photodiode), and light-emitting diode (LED). This opening chapter looks at the basic characteristics of these devices and shows a variety of ways of using standard diodes and rectifiers. Basic diode characteristics The solid-state diode is a two-terminal device that readily passes current in one direction, but blocks it in the other. Figure 1.1 shows a the conventional symbol and b the basic structure of the modern solid-state 'junction' diode; it is formed from a single p-n junction, and the 'p' terminal is known as the anode and the 'n' terminal as the cathode. Figure 1 .2 illustrates the basic characteristic of the diode. When it is forward biased (with the anode positive relative to the cathode) it acts A n o d e 9 A n o d e 1 Ρ η ό Cathode Cathode (a) (b) F i g u r e 1.1 Symbol (a) and structure (b) of solid-state diode 2 Diode, Transistor & FET Circuits Manual (а) (b) Figure 1.2 Diode conduction when (a) forward and (b) reverse-biased like a low resistance and readily passes current, but when reverse biased (with the anode negative relative to the cathode) it acts like a high resistance and passes near-zero current: this action is implied by the basic diode symbol, which resembles an arrow pointing in the direction of easy current conduction. Conventional junction diodes are made from either germanium or silicon materials. Figure 1.3 compares the basic characteristics of the two types of device when operated at a normal room temperature of 20°C; note the following important points.
eBook - PDF- J. David Irwin, R. Mark Nelms(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
In previous chapters, we introduced models for circuit elements such as resistors, capacitors, inductors, voltage sources, and current sources. Diodes can be modeled using two distinct approaches: a nonlinear model based on Eq. (16.1) or a linear approximation to the current–voltage characteristics of the device. There are three popular linear models for the diode: the ideal model, the constant-voltage model, and the piecewise-linear model. In the ideal model, with the diode symbol and i-υ curve illustrated in Figs. 16.6a and b, the device is treated as a simple switch. When acting like a closed switch, as shown in Fig. 16.6c, the diode is said to be forward-biased with υ D zero and i D positive. Alternatively, when reverse-biased, the condition in Fig. 16.6d, i D is zero, υ D is negative, and the “switch” is open. Thus, the Ideal Diode passes current from anode to cathode and blocks current in the opposite direction. The constant-voltage model, a modification of the ideal model, is a very popular model for pen-and-paper analysis. Here, the diode is modeled as a dc voltage source in series with an ide- al diode, as shown in Fig. 16.7a. The resulting i-υ characteristic is shown in Fig. 16.7b. When forward-biased, υ D = V on and is typically chosen at 0.6 or 0.7 V. Note that υ D values below V on produce no current. Therefore, the diode is reverse-biased for υ D < V on . Neither the ideal nor the constant-voltage model treats the finite slope of the i-υ curve in forward-bias. The piecewise-linear model does so by adding a series resistance to the con- stant-voltage model, as shown in Fig. 16.8a. Figure 16.8b shows the resulting i-υ characteris- tic where the slope is 1/R d . The diode is reverse-biased with no current until υ D reaches V F . At that point, the diode is forward-biased and current increases linearly with υ D . A comparison of the i-υ characteristics of these four models is shown in Fig. 16.9.
eBook - PDF- Behzad Razavi(Author)
- 2021(Publication Date)
- Wiley(Publisher)
Also, devices such as transistors fundamentally produce current in response to voltage. Exercise Plot the V/I characteristic of an Ideal Diode. Example 3-6 In the circuit of Fig. 3.8, each input can assume a value of either zero or +3 V. Determine the response observed at the output. Solution If V A = +3 V, and V B = 0, then we surmise that D 1 is forward-biased and D 2 , reverse-biased. Thus, V out = V A = +3 V. If uncertain, we can assume both D 1 and D 2 3.1 Ideal Diode 67 are forward-biased, immediately facing a conflict: D 1 enforces a voltage of +3 V at the output whereas D 2 shorts V out to V B = 0. This assumption is therefore incorrect. D 1 D 2 V R L out V V A B Figure 3.8 OR gate realized by diodes. The symmetry of the circuit with respect to V A and V B suggests that V out = V B = +3 V if V A = 0 and V B = +3 V. The circuit operates as a logical OR gate and was in fact used in early digital computers. Exercise Construct a three-input OR gate. Example 3-7 Is an Ideal Diode on or off if V D = 0? Solution An Ideal Diode experiencing a zero voltage must carry a zero current (why?). However, this does not mean it acts as an open circuit. After all, a piece of wire experiencing a zero voltage behaves similarly. Thus, the state of an Ideal Diode with V D = 0 is somewhat arbitrary and ambiguous. In practice, we consider slightly positive or negative voltages to determine the response of a diode circuit. Exercise Repeat the above example if a 1-Ω resistor is placed in series with the diode. Input/Output Characteristics Electronic circuits process an input and generate a corre- sponding output. It is therefore instructive to construct the input/output characteristics of a circuit by varying the input across an allowable range and plotting the resulting output. As an example, consider the circuit depicted in Fig. 3.9(a), where the output is defined as the voltage across D 1 . If V in < 0, D 1 is reverse biased, reducing the circuit to that in Fig.
eBook - PDF- Giovanni Saggio(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
319 Diode Circuits In this chapter, we will analyze the first electronic circuits , in particular (but not exclusively) based on diodes as semiconductor devices. Their function is to pro-cess a signal, that is, a time-varying electronic quantity (voltage, current, etc.) to which information is associated. Diode applications include rectification (Sections 9.1 and 9.2), voltage multipli-cation (Section 9.3), and wave shaping (Sections 9.4 and 9.5) of the signal. 9.1 RECTIFIERS Rectifiers are circuits that convert an alternating (including both signs) input signal to an unidirectional output signal (i.e., of a unique sign). So having an AC sinusoi-dal iso-frequency input signal, the rectifiers supply a DC pulsating multi-frequency output signal, whose harmonic content has more frequencies, including the zero frequency. Rectification is a nonlinear process implemented by the rectifiers. Most electronic devices require a plate DC voltage supply to work correctly, but in most cases we have single-phase AC mains. So, rectifiers are the basic circuit to convert AC to DC. 9.1.1 Half-Wave Rectifier The half-wave rectifier is a circuit that, given a pure sinusoidal input voltage, sup-plies an output positive (or negative) half-sine wave voltage. So, the signal is cut into its negative (or positive) part. Let’s consider the sinusoidal voltage signal v s = V sM sin( ω t ) 9 Principles of Analog Electronics 320 ( V sM is its amplitude) as input to the following circuit utilizing a single diode in series with a resistor (Figure 9.1). The output voltage is measured across the resistor. In such a circuit, we can only have current when the diode is forward biased beyond its threshold voltage V γ , so only when v s > V γ . This is also the condition for the current to flow in the resistor and for the output voltage v R , across the resistor, to be non-zero, as in Figure 9.2.
- Christopher Lavers, Edmund G.R. Kraal(Authors)
- 2014(Publication Date)
- Thomas Reed(Publisher)
With the advent of World War II, the silicon point-contact detector was developed for radar and other ‘spin-off s’ included the discovery of the properties of germanium and the improved crystal sensitivity arising from ‘doping’ a crystal. By the end of the war, research into semiconductors was well advanced, and the junction diode was demonstrated in 1941. To-date the most remarkable achievements have been in the fields of electronic equipment, power control devices and in miniaturisation of electronics, notably valued in the Apollo Space Programme in order to minimise the platform’s overall launch mass. To understand the action of a semiconductor, diode reference is once again made to electron theory, and the concept of electric current as an electron flow. The fundamental concepts are summarised as an introduction here to basic semiconductor theory. Basic theory The atom of a material consists of a nucleus (+ve charge) and planetary electrons (–ve charge). The nucleus has nearly all the mass of the atom and consists of both protons and neutrons with no electrical properties, but as forces of repulsion exist between +ve charged protons, the neutrons have the function of ‘holding’ the nucleus together. An atom contains equal numbers of protons and electrons with charges cancelling to make the atom neutral overall. Atoms of various elements contain different numbers of protons, neutrons and electrons and the greater the number of protons and neutrons in the nucleus, the greater the density of the substance. Electrons may be considered to move in planetary orbits and for the larger atoms, these electrons are arranged in various shells. The atom’s chemical properties may be explained in terms of the number and grouping of the planetary electrons. These ‘quantum shells’ are considered for simplicity to be concentric and 7 in number, distinguished by the sequential letters: K, L, M, N, O, P and Q respectively
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