Lecture 24 mosfet basics understanding with no math. Diodes and diode circuits tlt8016 basic analog circuits 20052006 11 3. Figure 5 depicts the real diode iv characteristic for a fairly typical silicon diode for positive diode voltages. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. Alan doolittle lecture 24 mosfet basics understanding with no math reading. This is the voltage required to reach a flat band diagram and sets an upper limit typically an overestimate for the voltage that can be applied to a diode before it burns itself up. They are also called pn diodes in analogy with vacuum diodes. Basic semiconductor physics, diodes, the nonlinear diode model, load line analysis, large signal diode models, offset diode model, transistors, large signal bjt model, load line analysis, small signal model and transistor amplification. At first glance, this looks like an insulator but the actual behavior is far more interesting, if we apply external voltages properly n n p collector emitter base moderately doped lightly doped, and very thin heavily doped. Ee lecture notes university of california, berkeley. Technical information, application notes and articles. The main characteristic of a pnjunction or a diode is that for positive voltages forward bias the diode is conduction, whereas for negative voltages reverse bias the current flow is blocked. Use the diode equation for that state to solve the circuit equations and find i.
Lecture notes microelectronic devices and circuits. It acts as a diode, which can serve in electronics as a rectifier, logic gate, voltage regulator zener diode. The ideal diode characteristic equation is known as the shockley equation, or simply the diode equation. A point contact diode with glass encapsulation and a schottky diode. The breakdown voltage of a zener diode is carefully set by controlling the doping level during manufacture. Exercise 4 a assuming a mps 3904 with exactly the characteristics of the curves 15 v, choose rc and rb to give ic given previously and vcc 10 ma, 7. The active portion of a zener diode is a semiconductor pn junction.
By using an led and a zener diode we can create a circuit which gives turns on the led when a voltage exceeds a certain value. Transistors now that we know about diodes, lets put two of them together, as follows. Would you recommend that this diode be used in a circuit which switches at 200khz. Diodes and diode circuits tlt8016 basic analog circuits 20052006 8 half wave rectifier with smoothing capacitor figure 3. Rectifier diodes are a vital component in power supplies where they are. Zener diode definition, vi characteristics, and breakdown. A zener diode is a type of diode that permits current to flow in the forward direction. Although it was ine of the first types of diode ever made, the schottky diode is widely sued because it is able to provide a very low forward voltage drop. The pn junction is a versatile element, which can be used as a. Diode behavior forward bias exponential behavior reverse bias breakdown controlled breakdown. Zener diodes with glass or black resin encapsulation. Hbd854 zener theory and design considerations handbook. The iv characteristics of a zener diode and the corresponding constantvoltage model are shown below. This reverse breakdown called zener breakdown occurs very sharply.
Introduction to semiconductors, doping, generationrecombination, te carrier concentrations. Iv characteristics, practical ohmic contacts, smallsignal capacitance pn junction diodes lecture 10. Typically, a silicon diode will have a vf around 0. Diode circuits and applications technology innovation and. Recipe for solving diode circuits state of diode is unknown before solving the circuit 1. Includes details of pn junction operation which is not covered in this course. As nouns, the terms diode and rectifier are almost interchangeable. The schottky diode or schottky barrier diode is used in a variety of circuits. The rectifier described above is used as the freewheel diode in a step down switching dcdc converter which is delivering 10a at 12v from a 48v supply. Alan doolittle intel develops worlds smallest, fastest cmos transistor santa clara, calif. Diodes and transistors university of california, berkeley. Diode theory diode as a conductor when a voltage is applied current will flow. A diode may be thought of as an electrical counterpart of a directional valve \check valve. Note to those familiar with a diode turn on voltage.
Basic electronics notes on vi characteristics of zener. Yellow and green indicator leds, an infra red photodiode. The large amount of current that will then flow could destroy the diode. For the zener diode we are using a model with a breakdown voltage vz and an. Diodes in the first lecture, we discussed linear circuit components resistors, capacitors, and inductors we found that we could build some electronic circuits using only these devices however, much of electronics in particular digital electronics depends upon nonlinear devices. This causes a excess drift current, and can be amplified to act as a receiver for optical signals from an optical fiber. Wei es154 lecture 8 18 perform the small signal analysis of the diode circuit biased with v dd by eliminating the dc sources and replacing the diode with a small signal resistance the resulting voltage divider gives. Separating out the dc or bias analysis and the signal analysis is a technique we will use extensively d d d s r r r. Peak inverse voltage peak inverse voltage piv across the diode. Basic diode electronics introduction to diodes the pn junction the pn junction is a homojunction between a ptype and an ntype semiconductor. A zener diode is a pn junction semiconductor device designed to operate in the reverse breakdown region. Zener diode characteristics in the forward region, the zener diode acts like a regular silicon diode, with a 0.
The semiconductor diode is a widely used electronics component found in many electronic circuit designs today. Zener diodes the simplest of all voltage regulators is the zener diode voltage regulator. Diodes and transistors pdf 28p this note covers the following topics. A simple zener diode voltage regulator in the voltage regulator the zener diode operates in the breakdown region, which ensures approximately constant voltage across it. Diodes in the first lecture, we discussed linear circuit components resistors, capacitors, and inductors we found that we could build some electronic circuits using only these devices however, much of electronics in particular. The transductance curve of a jfet is a graph of output current i d vs input voltage v gs as shown in fig. This causes a excess drift current, and can be amplified to act as. The termdiode is usually used for devices rated less than 0.
Every diode has a maximum reverse voltage breakdown voltage that cannot be exceeded without diode damage. Lecture 24 mosfet basics understanding with no math reading. Zener diode made specially to operate in the reverse breakdown region. When the diode is negative biased, no current can flow in the r, so vout 0. A zener diode is a type of diode that permits current to flow in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as zener knee voltage or zener voltage. Many types of diode are used for a wide range of applications. Smith detector zsimilarly to a solar cell, light hits a pn diode, and electrons and holes are generated. Pn junctions consist of two semiconductor regions of opposite type. Although there are many different types of diode which use the same basic structure of an area of ptype material meeting an area of ntype material, the different types are optimised to provide different characteristics which can be used in a variety of ways in many.
Piv is the peakinversevoltage of the diode forward bias occurs when the ptype block is connected to the positive terminal of the battery and the ntype is connected to the negative terminal of the battery, as shown below. Zener diodes diodes that can be made to conduct backwards. A check valve presents a small resistance if the pressure p 0, but blocks the ow i. Lecture 1 introduction to semiconductors and semiconductor. Zero current flows in a reversebiased ideal diode i. This effect, called zener breakdown, occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference. As a result the schottky barrier diode is used in a varity of applications from rf design to power. Write down all circuit equations and simplify as much as possible 2. A diodes iv characteristic is shown in figure 6 below.
Use the diode equation for that state to solve the circuit equations and find i d and v d 3. Although there are many different types of diode which use the same basic structure of an area of ptype material meeting an area of ntype material, the different types are optimised to provide different characteristics which can be used in a variety of ways in many electronic. They are both devices that allow current to flow only in one direction. Lightemitting diodes leds in a diode formed from a direct bandgap semiconductor, such as gallium. Zener diodes are designed to operate in the reverse breakdown region. Biasing the field effect transistor transductance curves. Making the usual assumptions calculate the peak current in the main switch. The type of diode also has some importance in defining the forward voltage drop. Poissons equation, work function, ms energy band diagrams lecture 9. Zener diode is a reversebiased heavilydoped pn junction diode which operates in the breakdown region. Zero voltage drop occurs across a forwardbiased ideal diode i. A specific diode s vf depends on what semiconductor material its made out of.
Currentvoltage characteristic of a zener diode with a breakdown voltage of 17 volt. To overcome this problem we make one terminal of the transistor common to both input and output terminals. Radhakrishna rao, department of electrical engineering,iit madras. The reverse breakdown of a pn junction may occur either due to zener effect or avalanche effect. The relationship is obtained by applying kvl and it is vs vg r im. Light emitting diode led graz university of technology. Since the reverse saturation current, is is typically very small 109 to 1015 a, the expression. Electronic devices chapter 3 special purpose diodes the zener diode a major application for zener diodes is as a type of voltage regulator for providing stable. For more protection consider the following clipping circuit. Diodes and diode circuits tlt8016 basic analog circuits 20052006 5 assumed states for analysis of ideal diode circuits example 3. This causes the holes to move toward the depletion region and the free electrons to move toward the depletion region. Appnotes and technical articles and documentations offer analysis, design ideas, reference designs, and recommendations to better implement diodes incorporateds products.
Due to this properties a diode can be used for several applications like rectifiers, sampling circuits, demodulators, logic gates and so on. What is the difference between the diode and the rectifier. Zener diode operates in reverse bias rb at the zener voltage v z. The depletion region shrinks allowing current to flow. Base, emitter and collector but when we connected it in a circuit, we require four terminals. Zener effect dominates at reverse voltages less than 5 volt whereas avalanche effect dominates above 5 v. Contd notes and anderson2 sections part 2 preface and sections 5. Excess populations and minimum carrier lifetime, photoconductivity. Zener diode is on when it operates on the zener region, i. A zener diode is a special diode that is optimized for operation in the breakdown region.
Aug 31, 2008 lecture series on electronics for analog signal processing i by prof. Determine the polarity of the voltage across the diode, then replace the diode with. Such junctions show a pronounced rectifying behavior. Basics currentvoltage characteristic of a zener diode with a breakdown voltage of 17 volt.
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