Basic Electronics PDF

Compiled by NKAY STUDY NANA KWABENA Intro. to Basic Electronics Instructors: G. S. KLOGO Emial: [email protected] Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA General Information...

Compiled by NKAY STUDY NANA KWABENA Intro. to Basic Electronics Instructors: G. S. KLOGO Emial: [email protected] Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA General Information Suggested pre-requisites: ▫ Basic course on applied electricity and linear algebra, Knowledge of electrical components will be an advantage. Course Content: ▫ Introduction to Electronics and its Applications ▫ Semiconductor Materials and Properties ▫ Semiconductor Diodes ▫ Semiconductor Diodes and Applications ▫ Bipolar Junction Transistor ▫ Transistor as an Amplifier ▫ Operational Amplifier ▫ Switching Theory and Logic Design Grading : ▫ Cont. Ass. : 30% Final Exams 70% Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Reference Books Electronic Principles by Albert Paul Malvino (copies can be found in both Engineering and Main Lib.) Electronic Engineering by Sanjay Sharma PhD. (copies can be found at Kingdom Books) etc Lecture Notes https://sites.google.com/site/klogoclass/home Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Intro. to Electricity and Electronics Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA What is Electronics Electronics is the branch of physics and technology concerned with the design of circuits using transistors and microchips, and with the behaviour and movement of electrons in a semiconductor, conductor, vacuum, or gas Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA System of Units Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Applications Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Atoms And Their Structure Everything is made of atoms The simplest of all atoms is the hydrogen atom. It is made up of two basic particles ▫ the proton ▫ the electron In all other elements the nucleus also contains neutrons which have no charge In every element the number of protons is equivalent to the number of electrons. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Coulomb’s Law Unlike charges attract; like charges repel. So there are forces of attraction acting in the atom between the protons in the nucleus and the electrons in the orbiting shells. This force is stronger when they are closer and weaker when they are far apart. Therefore it is easier to break away an electron that is distant from the nucleus. Also it is easier to break an electron from a shell that is incomplete and has fewer electrons. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Electricity An electron that breaks away from its atom is known as a Free Electron. These free electrons are known as charge carriers. The movement of free electrons is known as current of Electricty. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Some materials have strong attraction and refuse to lose electrons (have less free electrons), these are called insulators (air, porcelain, oils, Bakelite, rubber, teflon, glass, mica) Some materials have weak attractions and allow electrons to be lost, these are called conductors (silver, copper, gold, aluminium, tungsten, nickel, iron) Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Surplus of electrons is called a negative charge (-). A shortage of electrons is called a positive charge (+). A battery provides a surplus of electrons by chemical reaction. By connecting a conductor from the positive terminal to negative terminal electrons will flow. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Potential Difference(Voltage ) The applied potential difference ( measured in volts) of a voltage source in an electric circuit is the “pressure” needed to set the system in motion and “cause” the flow of charge or current through the electrical system. Compare this pressure to the pressure from a water tap connected to a hose Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Voltage Sources: Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Voltage is like differential pressure, always measure between two points. Measure voltage between two points or across a component in a circuit. When measuring DC voltage make sure polarity of meter is correct, positive (+) red, negative (-) black. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Ground Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Current Uniform flow of electrons thru a circuit is called current. WILL USE CONVENTIONAL FLOW NOTATION ON ALL SCHEMATICS Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA To measure current, must break circuit and install meter in line. Measurement is imperfect because of voltage drop created by meter. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Resistance The resistance of a material is the opposing force that a flowing charge encounters All materials have a resistance that is dependent on cross-sectional area, material type and temperature. A resistor dissipates power in the form of heat Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Various resistors types Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA When measuring resistance, remove component from the circuit. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Resistor Color Code Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Resistors in Circuits Series Looking at the current path, if there is only one path, the components are in series. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Resistors in Circuits Series R1  R2  Rn Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Resistors in Circuits Parallel If there is more than one way for the current to complete its path, the circuit is parallel Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Resistors in Circuits Parallel 1 R1 R2 R1  R2 1 1 1   R1 R2 Rn Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Resistors in Circuits Mixed If the path for the current in a portion of the circuit is a Series single path, and in R another portion of the circuit has Series Parallel multiple routes, the circuit is a mix of series and parallel. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Capacitance A capacitor is used to store charge for a short amount of time Capacitor Battery Unit = Farad Pico Farad - pF = 10-12F Micro Farad - uF = 10-6F Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Capacitor Defined A device that stores energy in electric field. Two conductive plates separated by a non conductive material. Electrons accumulate on one plate forcing electrons away from the other plate leaving a net positive charge. Think of a capacitor as very small, temporary storage battery. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Capacitor Physical Construction Capacitors are rated by: ▫ Amount of charge that can be held. ▫ The voltage handling capabilities. ▫ Insulating material between plates. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Capacitor Ability to Hold a Charge Ability to hold a charge depends on: ▫ Conductive plate surface area. ▫ Space between plates. ▫ Material between plates. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Capacitor Behavior in DC When exposed to DC, the capacitor charges and holds the charge as long as the DC voltage is applied. The capacitor essentially blocks DC voltage from passing through. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Capacitor Behavior in AC When AC current is applied, during one half of the cycle the capacitor accepts a charge in one direction. During the next half of the cycle, the capacitor is discharges then recharged in the reverse direction. During the next half cycle the pattern reverses. Essentially, it appears that AC current passes through a capacitor Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Capacitor Behavior A capacitor blocks the passage of DC A capacitor passes AC Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Capacitor Capacitance Value The unit of capacitance is the farad. ▫ A single farad is a huge amount of capacitance. ▫ Most electronic devices use capacitors that have a very tiny fraction of a farad. Common capacitance ranges are: ▫ Micro  - 10-6 ▫ Nano n - 10-9 ▫ Pico p - 10-12 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Capacitor Capacitance Value Capacitor identification depends on the capacitor type. Could be color bands, dots, or numbers. Wise to keep capacitors organized and identified to prevent a lot of work trying to re-identify the values. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Capacitors in Circuits + Two physical factors affect capacitance Charged plates far apart values. ▫ Plate spacing - ▫ Plate surface area In series, plates are far apart making capacitance less C1C2 C1  C2 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Capacitors in Circuits In parallel, the + surface area of the plates add up to be greater, and close together. - This makes the C1  C2 capacitance more the Capacitor Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Inductor There are two fundamental principles of electronics: 1. Moving electrons create a magnetic field. 2. Moving or changing magnetic fields cause electrons to move. An inductor is a coil of wire through which electrons move, and energy is stored in the resulting magnetic field. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Inductor Like capacitors, inductors temporarily store energy. Unlike capacitors: ▫ Inductors store energy in a magnetic field, not an electric field. ▫ When the source of electrons is removed, the magnetic field collapses immediately. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Inductor Inductors are simply coils of wire. ▫ Can be air wound (nothing in the middle of the coil) ▫ Can be wound around a permeable material (material that concentrates magnetic fields) ▫ Can be wound around a circular form (toroid) Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Inductor Inductance is measured in Henry(s). A Henry is a measure of the intensity of the magnetic field that is produced. Typical inductor values used in electronics are in the range of milli Henry (1/1000) and micro Henry (1/1,000,000) Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Inductor The amount of inductance is influenced by a number of factors: ▫ Number of coil turns. ▫ Diameter of coil. ▫ Spacing between turns. ▫ Size of the wire used. ▫ Type of material inside the coil. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Inductor Performance With DC Currents When DC current is applied to an inductor, the wire in the inductor momentarily appears as a short circuit and maximum current flows. As the magnetic field builds (changes) there is a tendency for the current flow to slow down (due to an opposition cause the the changing magnetic field). Finally, the magnetic field is at its maximum and the current flows to maintain the field. As soon as the current source is removed, the magnetic field begins to collapse and creates a rush of current in the other direction, sometimes at very high voltages. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Inductor Performance With AC Currents When AC current is applied to an inductor, during the first half of the cycle, the magnetic field builds as if it were a DC voltage. During the next half of the cycle, the current is reversed and the magnetic field first has to decrease the reverse polarity in step with the changing current. Depending on the value of inductance, these forces can work against each other, making for a less than simple situation. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA The Inductor Because the magnetic field surrounding an inductor can cut across another inductor in close proximity, the changing magnetic field in one can cause current to flow in the other … the basis of transformers Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Laws and Principles of Electricity and Electronics Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Laws and Rules Ohm’s Kirchhoff’s Voltage Divider Current Divider Thevenin’s Norton’s Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Reminder: Elements in series Two elements are in series if 1. They have only one terminal in common (i.e., one lead of one is connected to only one lead of the other). 2. The common point between the two elements is not connected to another current-carrying element. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Reminder: Resistors in series The total resistance of a series circuit is the sum of the resistance levels. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Ohm’s Law The mathematical relationship ▫ E=I*R Doing the math Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Ohm’s Law In 1827 George Ohm proved there was a direct relationship between Voltage (E), Current (I), and Resistance (R) in an electrical circuit. This relationship is known as Ohm’s Law. Ohm’s Law states that current in a circuit is proportional to the voltage and inversely proportional to the resistance. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Ohm’s Law There is a E  I *R mathematical relationship between E the three components of R electricity. That relationship is I Ohm’s Law. ▫ E = volts E ▫ R = resistance in ohms ▫ I = current in amps I R Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Ohm’s Law E = Voltage - Volts I = Current - Amps R = Resistance or Reactance (Impedence) - Ohms Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Question a. Find the total resistance for the series circuit of the figure below b. Calculate the source current Is. c. Determine the voltages V1, V2, and V3. d. Calculate the power dissipated by R1, R2, and R3. e. Determine the power delivered by the source, and compare it to the sum of the power levels of part (d). Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Power Transforming energy from one form to another is called work. The greater the energy transformed, the more work that is done. There are six basic forms of energy and they are light, heat, magnetic, chemical, electrical, and mechanical energy. The unit for measuring work is called the Joule (J). Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Power Power (P) is the rate at which work is performed and is measured by the unit called Watt (W). Watts = Joules per second. The output Power, or power ratings of electrical, electronic or mechanical devices can be expressed in Watts (W) and describes the number of Joules of energy converted every second. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Power Power is the rate at which electric energy (W) is converted to some other form and can be expressed mathematically as P = I x V. This formula states that the amount of power delivered to a device is dependent on the electrical pressure (or voltage applied across the device) and the current flowing through the device. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Power Formula The Power Formula is the relationship between Power (P), Voltage (E), and Current (I). P P = Power -Watts E = Voltage - Volts I = Current - Amps E I Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Power Formula The Power Formula states that if the voltage in a circuit changes, the current in the circuit also changes. The power required from a circuit changes any time loads are added (power increases) or removed (power decreases). The Power Formula is used when troubleshooting and to predict circuit characteristics before power is applied. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Combining Ohm’s Law and Power Formula Ohm’s Law and the Power Formula may be combined mathematically and written as any combination of Voltage (E), Current (I), Resistance (R), or Power (P). Ohm’s Law and the Power Formula are limited to circuits in which electrical resistance is the only significant opposition to the flow of current. This limitation includes all DC circuits and AC circuits that do no contain a significant amount of inductance and/or capacitance – which we will learn about later. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Combining Ohm’s Law and Power Formula Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 64 Kirchhoff’s Voltage Law (KVL) The algebraic sum of the voltage that rises and drops around a closed loop is equal to zero ET - V1 - V2 - V3 - ∙∙∙ - Vn = 0 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 65 Kirchhoff’s Voltage Law (KVL) Another way of stating KVL is: ▫ Summation of voltage rises is equal to the summation of voltage drops around a closed loop V1 + V2 + V3 + ∙∙∙ + Vn = ET Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 66 Kirchhoff’s Voltage Law (KVL) the applied voltage of a series circuit equals the sum of the voltage drops across the series elements. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 67 Kirchhoff’s Voltage Law (KVL) a. Find RT. b. Find I. c. Find V1 and V2. d. Find the power to the 4- and 6- resistors. e. Find the power delivered by the battery, and compare it to that dissipated by the 4- and 6- resistors combined. f. Verify Kirchhoff’s voltage law (clockwise direction). Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Voltage Divider Rule R1 v1  R1i  v total R1  R2  R3 R2 v 2  R2 i  v total R1  R2  R3 The voltage across the resistive elements will divide as the magnitude of the resistance levels. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Application of the Voltage-Division Principle R1 v1  vtotal R1  R2  R3  R4 1000  15 1000  1000  2000  6000  1.5V Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Simplifying the Voltage Divider Rule Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Reminder: Elements in Parallel Two elements, branches, or networks are in parallel if they have two points in common Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Reminder: Elements in Parallel Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Reminder: Resistors in parallel For parallel resistors, the total conductance is the sum of the individual conductances. 𝟏 G= 𝑹 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Reminder: Resistors in parallel The voltage across parallel elements is the same. For single-source parallel networks, the source current (Is ) is equal to the sum of the individual branch currents. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Question: Resistors in parallel Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA KIRCHHOFF’S CURRENT LAW Kirchhoff’s current law (KCL) states that the algebraic sum of the currents entering and leaving an area, system, or junction is zero. In other words, the sum of the currents entering an area, system, or junction must equal the sum of the currents leaving the area, system, or junction. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA KIRCHHOFF’S CURRENT LAW Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Current Divider Principle Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Current Division Principle v R2 i1   itotal R1 R1  R2 v R1 i2   itotal R2 R1  R2 It can be also simplified as (Especially considering multiple resistors in parallel) Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Application of the Current-Division Principle R2 R3 30  60 Req    20 R2  R3 30  60 Req 20 i1  is  15  10A R1  Req 10  20 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Voltage division Voltage division and current division Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Current division Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Although they are very important concepts, series/parallel equivalents and the current/voltage division principles are not sufficient to solve all circuits. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Thevenin’s Theorem Thevenin’s Theorem – any resistive circuit or network, no matter how complex, can be represented as a voltage source in series with a source resistance Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Thevenin’s Theorem Thevenin Voltage (VTH) – the voltage present at the output terminals of the circuit when the load is removed Insert Figure 7.18 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Thevenin’s Theorem Thevenin Resistance (RTH) – the resistance measured across the output terminals with the load removed Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Thévenin Equivalent Circuits Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Thévenin Equivalent Circuits Vt  voc voc Rt  isc Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Thévenin Equivalent Circuits Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Finding the Thévenin Resistance Directly When zeroing a voltage source, it becomes a short circuit. When zeroing a current source, it becomes an open circuit. We can find the Thévenin resistance by zeroing the sources in the original network and then computing the resistance between the terminals. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Computation of Thévenin resistance Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA Equivalence of open-circuit and Thévenin voltage Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA A circuit and its Thévenin equivalent Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Applications of Thevenin’s Theorem Load Voltage Ranges – Thevenin’s theorem is most commonly used to predict the change in load voltage that will result from a change in load resistance Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Applications of Thevenin’s Theorem Maximum Power Transfer ▫ Maximum power transfer from a circuit to a variable load occurs when the load resistance equals the source resistance ▫ For a series-parallel circuit, maximum power occurs when RL = RTH Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Applications of Thevenin’s Theorem Multiload Circuits Insert Figure 7.30 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Applications of Thevenin’s Theorem Example: Find the Thevenin equivalent circuit for the network in the shaded area of the circuit below Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Norton’s Theorem Norton’s Theorem – any resistive circuit or network, no matter how complex, can be represented as a current source in parallel with a source resistance Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Norton’s Theorem Norton Current (IN) – the current through the shorted load terminals Insert Figure 7.35 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Computation of Norton current Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Norton’s Theorem Norton Resistance (RN) – the resistance measured across the open load terminals (measured and calculated exactly like RTH) Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Norton’s Theorem Norton-to-Thevenin and Thevenin-to-Norton Conversions Insert Figure 7.39 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Step-by-step Thévenin/Norton- Equivalent-Circuit Analysis 1. Perform two of these: a. Determine the open-circuit voltage Vt = voc. b. Determine the short-circuit current In = isc. c. Zero the sources and find the Thévenin resistance Rt looking back into the terminals. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 2. Use the equation Vt = Rt In to compute the remaining value. 3. The Thévenin equivalent consists of a voltage source Vt in series with Rt. 4. The Norton equivalent consists of a current source In in parallel with Rt. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Maximum Power Transfer The load resistance that absorbs the maximum power from a two-terminal circuit is equal to the Thévenin resistance. Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA Power transfer between source and Graphical representation of load maximum power transfer Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA …that’s all folks… …thanks for your time… Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 1 EE 152: Basic Electronics (Semiconductor Basics) Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 2 Outline Introduction Basic Semiconductor Concepts ▫Intrinsic ▫Doping ▫Extrinsic ◦N-type ◦P-type ▫Carrier movement Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 3 Electronic Materials The goal of electronic materials is to generate and control the flow of an electrical current. Electronic materials include: 1. Conductors: have low resistance which allows electrical current flow 2. Insulators: have high resistance which suppresses electrical current flow 3. Semiconductors: can allow or suppress electrical current flow Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 4 Conductors, semiconductors and insulators Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 5 Conductors Good conductors have low resistance so electrons flow through them with ease. Best element conductors include: ▫ Copper, silver, gold, aluminum, & nickel Alloys are also good conductors: ▫ Brass & steel Good conductors can also be liquid: ▫ Salt water Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 6 Conductor Atomic Structure The atomic structure of good conductors usually includes only one electron in their outer shell. ▫ It is called a valence electron. ▫ It is easily striped from the atom, producing current flow. Copper Atom Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 7 Insulators Insulators have a high resistance so current does not flow in them. Good insulators include: ▫ Glass, ceramic, plastics, & wood Most insulators are compounds of several elements. The atoms are tightly bound to one another so electrons are difficult to strip away for current flow. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 8 Semiconductors Semiconductors are materials that essentially can be conditioned to act as good conductors, or good insulators, or any thing in between. Common elements such as carbon, silicon, and germanium are semiconductors. Silicon is the best and most widely used semiconductor. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 9 What is a Semiconductor? A semiconductor is a material with conducting properties between those of a good insulator (e.g. glass) and a good conductor (e.g. copper). The most commonly used semiconductor is silicon. Low resistivity => “conductor” High resistivity => “insulator” Intermediate resistivity => “semiconductor” ▫ conductivity lies between that of conductors and insulators ▫ generally crystalline in structure for IC devices  In recent years, however, non-crystalline semiconductors have become commercially very important polycrystalline amorphous crystalline Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 10 Semiconductor Elements in the Periodic Table Group III Group IV Group V +3 +4 +5 Boron (B) Carbon (C) Nitrogen (N) Aluminium (Al) Silicon (Si) Phosphorus (P) Germanium Gallium (Ga) Arsenic (As) (Ge) Indium (In) Tin (Sn) Antimony (Sb) Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Semiconductor Valence Orbit The main characteristic of a semiconductor element is that it has four electrons in its outer or valence orbit. 11 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Crystal Lattice Structure The unique capability of semiconductor atoms is their ability to link together to form a physical structure called a crystal lattice. The atoms link together with one another sharing their outer electrons. 2D Crystal Lattice These links are called Structure covalent bonds. 12 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 3D Crystal Lattice Structure 13 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 14 Silicon Atomic density: 5 x 1022 atoms/cm3 Each silicon atom has an outer shell with four valence electrons and four vacancies (It is a tetravalent element). In intrinsic (pure) silicon, atoms join together by forming covalent bonds. Each atom shares its valence electrons with each of four adjacent neighbours effectively filling its outer shell. When temperature goes up, electrons can become free to move about the Si lattice. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 15 Electronic Properties of Si  Silicon is a semiconductor material. ▫ Pure Si has a relatively high electrical resistivity at room temperature.  There are 2 types of mobile charge-carriers in Si: ▫ Conduction electrons are negatively charged; ▫ Holes are positively charged.  The concentration (#/cm3) of conduction electrons & holes in a semiconductor can be modulated in several ways: 1. by adding special impurity atoms ( dopants ) 2. by applying an electric field 3. by changing the temperature 4. by irradiation Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 16 Thermal ionization Valence electron---each silicon atom has four valence electrons Covalent bond---two valence electrons from different two silicon atoms form the covalent bond  Be intact at sufficiently low temperature  Be broken at room temperature Free electron---produced by thermal ionization, move freely in the lattice structure. Hole---empty position in broken covalent bond, can be filled by free electron, positive charge Carriers A free electron is negatively charge and a hole is positively charge. Both of them can move in the crystal structure. They can conduct electric circuit. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 17 Recombination Some free electrons filling the holes results in the disappearance of free electrons and holes. Thermal equilibrium At a certain temperature, the recombination rate is equal to the ionization rate. So the concentration of the carriers is able to be calculated. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 18 Carrier concentration in thermal equilibrium n  p  ni 3  EG kT ni  BT e 2 At room temperature(T=300K) ni  1.5 1010 carriers/cm3 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 19 Semiconductors can be Insulators If the material is pure semiconductor material like silicon, the crystal lattice structure forms an excellent insulator since all the atoms are bound to one another and are not free for current flow. Good insulating semiconductor material is referred to as intrinsic. Since the outer valence electrons of each atom are tightly bound together with one another, the electrons are difficult to dislodge for current flow. Silicon in this form is a great insulator. Semiconductor material is often used as an insulator. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 20 Intrinsic Semiconductors Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 21 Intrinsic Semiconductors The structure has zero overall charge The complete nature of the structure means that at absolute zero temperature (0 K) none of the electrons is available for conduction…thus far the material is an insulator. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 22 Intrinsic Semiconductors At room temperature some of the electrons are able to acquire sufficient thermal energy to break free from their bond. Whenever an electron leaves its position in the lattice it leaves a vacancy known as a hole. The process is known as electron-hole pair generation Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 23 Intrinsic Semiconductors Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 24 Electron-Hole Pair Generation When a conduction electron is thermally generated, a “hole” is also generated. A hole is associated with a positive charge, and is free to move about the Si lattice as well. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 25 Carrier Concentrations in Intrinsic Si The “band-gap energy” Eg is the amount of energy needed to remove an electron from a covalent bond. The concentration of conduction electrons in intrinsic silicon, ni, depends exponentially on Eg and the absolute temperature (T):  Eg ni  5.2 10 T 15 3/ 2 exp electrons / cm 3 2kT ni  11010 electrons / cm 3 at 300K ni  11015 electrons / cm 3 at 600K Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 26 Intrinsic Semiconductors A freed electron can move through the body of the material until it encounters another broken bond where it is drawn in to complete the bond or recombines. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 27 Intrinsic Semiconductors At a given temperature there is a dynamic equilibrium between thermal electron-hole generation and the recombination of electrons and holes As a result the concentration of electrons and holes in an intrinsic semiconductor is constant at any given temperature. The higher the temperature the more electron- hole pairs that are present. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 28 Intrinsic Semiconductors Two mechanisms for conduction become possible when a bond breaks: 1. Due to the movement of the freed electron. 2. Due to neighbouring electrons moving into the hole leaving a space behind it. (This can be most simply thought of as movement of the hole, a single moving positive charge carrier even though it is actually a series of electrons that move. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 29 Intrinsic Semiconductors When an electric field (voltage) is applied, the holes move in one direction and the electrons in the other. However both current components are in the direction of the field. The conduction is ohmic, i.e. current is proportional to the applied voltage (field) Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 30 Intrinsic Semiconductors The proportion of freed electrons is very small indeed: In silicon the energy EG required to free an electron is 1.2eV The mean thermal energy (kT) is only 25meV at room temperature (1/40 eV) The proportion of freed electrons varies exponentially (-EG /kT). Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 31 Intrinsic Semiconductors For an intrinsic semiconductor the number of electron and hole carriers, and thus the conductivity, increases rapidly with temperature. This is not very useful. Hence we dope the material to produce an extrinsic semiconductor. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 32 Doping To make the semiconductor conduct electricity, other atoms called impurities must be added. “Impurities” are different elements. This process is called doping. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 33 Extrinsic Semiconductors Intrinsic conduction is very small. Conductivity levels can be raised and controlled by doping with minute levels of impurity atoms to give extrinsic or doped semiconductors. Extrinsic semiconductors may be further divided into either n-type or p-type Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Semiconductors can be Conductors An impurity, or element like arsenic, has 5 valence electrons. Adding arsenic (doping) will allow four of the arsenic valence electrons to bond with the neighboring silicon atoms. The one electron left over for each arsenic atom becomes available to conduct current flow. 34 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 35 Resistance Effects of Doping If you use lots of arsenic atoms for doping, there will be lots of extra electrons so the resistance of the material will be low and current will flow freely. If you use only a few boron atoms, there will be fewer free electrons so the resistance will be high and less current will flow. By controlling the doping amount, virtually any resistance can be achieved. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Another Way to Dope You can also dope a semiconductor material with an atom such as boron that has only 3 valence electrons. The 3 electrons in the outer orbit do form covalent bonds with its neighboring semiconductor atoms as before. But one electron is missing from the bond. This place where a fourth electron should be is referred to as a hole. The hole assumes a positive charge so it can attract electrons from some other source. Holes become a type of current carrier like the electron to support current flow. 36 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 37 Types of Semiconductor Materials The silicon doped with extra electrons is called an “N type” semiconductor. ▫ “N” is for negative, which is the charge of an electron. Silicon doped with material missing electrons that produce locations called holes is called “P type” semiconductor. ▫ “P” is for positive, which is the charge of a hole. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 38 N-type Semiconductors An n-type impurity atom has five outer (valence) electrons, rather than the four of silicon. Only four of the outer electrons are required for covalent bonding. The fifth is much more easily detached from the parent atom. As the energy needed to free the fifth electron is smaller than the thermal energy at room temperature virtually all are freed. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 39 N-type Semiconductors EXTRA ELECTRON FREE AT ROOM TEMP. +4 +4 +4 +4 +5 + 4 +4 +4 +4 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 40 Carrier concentration for n type a) Thermal equilibrium equation nn 0  pn 0  ni 2 b) Electric neutral equation nn0  pn0  N D Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 41 P-type Semiconductors Here the doping atom has only three electrons in its outer shell. It is relatively easy for an electron from a neighbouring atom to move in, so releasing a hole at its parent atom. The freed hole is available for conduction. The energy needed to free the electron from its parent is usually small compared to the thermal energy so each impurity atom contributes one hole for conduction (fully ionised). Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 42 P-type Semiconductors A neighbouring electron can move here. This creates a hole where the +3 electron came from. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 43 Carrier concentration for p type a) Thermal equilibrium equation p p 0  n p 0  ni 2 b) Electric neutral equation p p0  np0  N A Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 44 Summary of Charge Carriers Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 45 Electron and Hole Concentrations Under thermal equilibrium conditions, the product of the conduction-electron density and the hole density is ALWAYS equal to the square of ni: np  ni 2 N-type material P-type material n  ND p  NA 2 2 n n p i n i ND NA Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Electron and Hole Densities np  ni 2 Majority Carriers : p  NA 2 Minority Carriers : n n i Majority Carriers : NA n  ND Minority Carriers : 2 n p i ND The product of electron and hole densities is ALWAYS equal to the square of intrinsic electron density regardless of doping levels. 46 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 47 Carriers Movement There are two mechanisms by which holes and free electrons move through a silicon crystal. Drift--- The carrier motion is generated by the electrical field across a piece of silicon. This motion will produce drift current. Diffusion--- The carrier motion is generated by the different concentration of carrier in a piece of silicon. The diffused motion, usually carriers diffuse from high concentration to low concentration, will give rise to diffusion current. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 48 Diffusion and Diffusion Current diffusion A bar of intrinsic silicon (a) in which the hole concentration profile shown in (b) has been created along the x-axis by some unspecified mechanism. The diffusion current density is proportional to the slope of the concentration curve, or the concentration gradient. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Current Flow in N-type Semiconductors The DC voltage source has a positive terminal that attracts the free electrons in the semiconductor and pulls them away from their atoms leaving the atoms charged positively. Electrons from the negative terminal of the supply enter the semiconductor material and are attracted by the positive charge of the atoms missing one of their electrons. Current (electrons) flows from the positive terminal to the negative terminal. 49 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Current Flow in P-type Semiconductors Electrons from the negative supply terminal are attracted to the positive holes and fill them. The positive terminal of the supply pulls the electrons from the holes leaving the holes to attract more electrons. Current (electrons) flows from the negative terminal to the positive terminal. Inside the semiconductor current flow is actually by the movement of the holes from positive to negative. 50 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 51 Temperature sensitivity In both types of extrinsic semiconductor virtually all available charge carries are freed from their parent atoms at room temperature. Temperature variations thus make little difference to the conductivity . For intrinsic conductivity the number of carriers, and thus , increases rapidly with temperature. For both extrinsic and intrinsic mechanisms the conductivity is zero at T=0 K Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 52 Terminology donor: impurity atom that increases n acceptor: impurity atom that increases p N-type material: contains more electrons than holes P-type material: contains more holes than electrons majority carrier: the most abundant carrier minority carrier: the least abundant carrier intrinsic semiconductor: n = p = ni extrinsic semiconductor: doped semiconductor Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 53 In Summary In its pure state, semiconductor material is an excellent insulator. The commonly used semiconductor material is silicon. Semiconductor materials can be doped with other atoms to add or subtract electrons. An N-type semiconductor material has extra electrons. In an N-type semiconductor, conduction is mainly due to electrons (negative charges). Positive charges (holes) are the minority carriers. A P-type semiconductor material has a shortage of electrons with vacancies called holes. In a P-type semiconductor, conduction is mainly due to holes (positive charges). Negative charges (electrons) are the minority carriers. The heavier the doping, the greater the conductivity or the lower the resistance. By controlling the doping of silicon the semiconductor material can be made as conductive as desired. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA …that’s all folks… …thanks for your time… Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 1 PN-Junction Diode Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 2 Outline The PN-Junction Diode Analysis of diode circuits I-V characteristic of pn junction Terminal characteristic of junction diode. Physical operation of diode. Applications of diode circuits  Rectification ▫ Half wave Rectifiers ▫ Full wave Rectifiers ▫ Centre-tap ▫ Bridge Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 3 Previous Lecture Semiconductor ▫ Intrinsic ▫ Doping ▫ Extrinsic  N-type  P-type Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Intrinsic (pure) Semiconductors A hole  Intrinsic(pure) silicon A free electron An electron-hole pair is created when an electron get excited by thermal or light energy; Recombination occurs when an electron loses energy and falls back into a hole. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Intrinsic (pure) Semiconductors Holes also conduct current. In reality, it’s the movement of all the other electrons. The hole allows this motion. Holes have positive charge. Current flows in the same direction as the holes move.  Both electrons and holes carry current-- carriers.  In intrinsic semiconductors the electron and hole concentrations are equal because carriers are created in pairs  The intrinsic concentration depends exponentially on temperature.  At room temp (300K), the intrinsic carrier concentration of silicon is: ni  1.5  1010 / cm 3 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Phosphorus Doping (N-type) Phosphorus has 5 valence electrons. P atoms will sit in the location of a Si atom in the lattice, to avoid breaking symmetry, but each will have an extra electron that does not bond in the same way. And these extra electrons are easier to excite (and can move around more easily) These electrons depends on the amounts of the two materials. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Phosphorus Doping (N-type) Electrons---Majority carrier. Holes---Minority carrier Phosphorus---Donor materials. In equilibrium, pn  pi ni  pi2  ni2 At room temp (300K), if 1/1010 donors are added to the intrinsic silicon, then the electron carrier concentration is about 1013cm－3; the hole carrier concentration is about 106cm－3. Phosphorus   89.3  cm; Intrinsic silicon   2.14  10   cm 5 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Boron Doping (P-type) Holes---Majority carrier; Electrons---Minority carrier Boron---acceptor materials. Boron has 3 valence electrons. B will sit at a lattice site, but the adjacent Si atoms lack an electron to fill its shell. This creates a hole. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA PN Junction  N-type materials: Doping Si with a Group V element, providing extra electrons (n for negative).  P-type materials: Doping Si with a Group III element, providing extra holes (p for positive). What happens when P-type meets N-type? Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA PN Junction What happens when P-type meets N-type? Holes diffuse from the P-type into the N-type, electrons diffuse from the N-type into the P-type, creating a diffusion current. Once the holes [electrons] cross into the N-type [P-type] region, they recombine with the electrons [holes]. This recombination “strips” the n-type [P-type] of its electrons near the boundary, creating an electric field due to the positive and negative bound charges. The region “stripped” of carriers is called the space-charge region, or depletion region. V0 is the contact potential that exists due to the electric field. Typically, at room temp, V0 is 0.5~0.8V. Some carriers are generated (thermally) and make their way into the depletion region where they are whisked away by the electric field, creating a drift current. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA PN Junction What happens when P-type meets N-type?  There are two mechanisms by which mobile carriers move in semiconductors – resulting in current flow – Diffusion Majority carriers move (diffuse) from a place of higher concentration to a place of lower concentration – Drift Minority carrier movement is induced by the electric field.  In equilibrium, diffusion current (ID) is balanced by drift current (IS). So, there is no net current flow. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA PN Junction (Diode) When N-type and P-type dopants are introduced side-by-side in a semiconductor, a PN junction or a diode is formed. 12 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Diode’s Three Operation Regions In order to understand the operation of a diode, it is necessary to study its three operation regions: equilibrium, reverse bias, and forward bias. 13 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Current Flow Across Junction: Diffusion Because each side of the junction contains an excess of holes or electrons compared to the other side, there exists a large concentration gradient. Therefore, a diffusion current flows across the junction from each side. 14 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Depletion Region As free electrons and holes diffuse across the junction, a region of fixed ions is left behind. This region is known as the “depletion region.” 15 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Current Flow Across Junction: Equilibrium I drift , p  I diff , p I drift ,n  I diff ,n At equilibrium, the drift current flowing in one direction cancels out the diffusion current flowing in the opposite direction, creating a net current of zero. The figure shows the charge profile of the PN junction. 16 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Current Flow Across Junction: Drift The fixed ions in depletion region create an electric field that results in a drift current. 17 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 18 Biasing a PN Junction Diode Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA Appliying bias to p-n junction + -  How current flows through the p-n p n junction when a bias (voltage) is forward bias applied.  The current flows all the time whenever a voltage source is - + connected to the diode. But the current flows rapidly in forward bias, however p n a very small constant current flows in reverse bias case. reverse bias Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA Appliying bias to p-n junction I(current) Reverse Bias Forward Bias Vb I0 V(voltage) Vb ; Breakdown voltage I0 ; Reverse saturation current  There is no turn-on voltage because current flows in any case. However , the turn-on voltage can be defined as the forward bias required to produce a given amount of forward current.  If 1 m A is required for the circuit to work, 0.7 volt can be called as turn-on voltage. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 21 Biasing PN Junction Diode Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA Appliying bias to p-n junction VF forward voltage VR reverse voltage When a voltage is applied to a diode , bands move and the behaviour of the bands with applied forward and reverse fields are shown in previous diagram. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Diode in Forward Bias Add more majority carriers to both sides shrink the depletion region lower V0 diffusion current increases. Decrease the built-in potential, lower the barrier height. Increase the number of carriers able to diffuse across the barrier Diffusion current increases Drift current remains the same. The drift current is essentially constant, as it is dependent on temperature. Current flows from p to n When the N-type region of a diode is at a lower potential than the P-type region, the diode is in forward bias. The depletion width is shortened and the built-in electric field decreased. 23 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA  Junction potential reduced  Enhanced hole diffusion from p-side to n-side compared with the equilibrium case.  Enhanced electron diffusion from n-side to p-side compared with the equilibrium case.  Drift current flow is similar to the equilibrium case.  Overall, a large diffusion current is able to flow.  Mnemonic. Connect positive terminal to p-side for forward bias.  Drift current is very similar to that of the equilibrium case. This current is due to the minority carriers on each side of the junction and the movement minority carriers is due to the built in field accross the depletion region. Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA Qualitative explanation of forward bias + - Junction potential is reduced p - + n By forward biasing a large - + number of electrons are pn injected from n-side to p-side Carrier Density np accross the depletion region and these electrons become pno minority carriers on p-side, npo and the minority recombine with majority holes so that the number of injected minority electrons decreases (decays) exponentially with distance p-n junction in forward bias into the p-side. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Similarly, by forward biasing a large number of holes are injected from p-side to n-side across the DR. These holes become minority carriers at the depletion region edge at the n-side so that their number (number of injected excess holes) decreases with distance into the neutral n-side. In summary, by forward biasing in fact one injects minority carriers to the opposite sides. These injected minorites recombine with majorities. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Forward Bias Condition: Summary In forward bias, there are large diffusion currents of minority carriers through the junction. However, as we go deep into the P and N regions, recombination currents from the majority carriers dominate. These two currents add up to a constant value. 27 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Diode in Reverse Bias Increase the built-in potential, increase the barrier height. Decrease the number of carriers able to diffuse across the barrier. Diffusion current decreases. Drift current remains the same Almost no current flows. Reverse leakage current, IS, is the drift current, flowing from N to P. When the N-type region of a diode is connected to a higher potential than the P-type region, the diode is under reverse bias, which results in wider depletion region and larger built-in electric field across the junction. 28 Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA Reverse Bias  Junction potential increased  Reduced hole diffusion from p-side to n-side compared with the equilibrium case.  Reduced electron diffusion from n-side to p-side compared with the equilibrium case  Drift current flow is similar to the equilibrium case.  Overall a very small reverse saturation current flows.  Mnemonic. Connect positive terminal to n-side for reverse bias. Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA p-n junction in reverse bias The flow of these minorities produces the reverse saturation current and this current increases exponentially with temperature but it is independent of applied reverse voltage. I(current) Forward Bias Vb I0 V(voltage) VB ; Breakdown voltage I0 ; Reverse saturation current Reverse Bias Drift current Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA PN Junction Diode I-V Characteristic Typical PN junction diode volt-ampere characteristic is shown on the left. – In forward bias, the PN junction has a “turn on” voltage based on the “built-in” potential of the PN junction. turn on voltage is typically in the range of 0.5V to 0.8V – In reverse bias, the PN junction conducts essentially no current until a critical breakdown voltage is reached. The breakdown voltage can range from 1V to 100V. Breakdown mechanisms include avalanche and zener tunneling. The current and voltage relationship of a PN junction is exponential in forward bias region, and relatively constant in reverse bias region. Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA Junction breakdown or reverse breakdown An applied reverse bias (voltage) will result in a small current to flow through the device. At a particular high voltage value, which is called as breakdown voltage VB, large currents start to flow. If there is no current limiting resistor which is connected in series to the diode, the diode will be destroyed. There are two physical effects which cause this breakdown. 1) Zener breakdown is observed in highly doped p-n junctions and occurs for voltages of about 5 V or less. 2) Avalanche breakdown is observed in less highly doped p-n junctions. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Reverse Breakdown When a large reverse bias voltage is applied, breakdown occurs and an enormous current flows through the diode. 33 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Zener breakdown Zener breakdown occurs at highly doped p-n junctions with a tunneling mechanism. In a highly doped p-n junction the conduction and valance bands on opposite side of the junction become so close during the reverse-bias that the electrons on the p-side can tunnel into the n-side. Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA Avalanche Breakdown Avalanche breakdown mechanism occurs when electrons and holes moving through the DR and acquire sufficient energy from the electric field to break a bond i.e. create electron-hole pairs by colliding with atomic electrons within the depletion region. The newly created electrons and holes move in opposite directions due to the electric field and thereby add to the existing reverse bias current. This is the most important breakdown mechanism in p-n junction. Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Zener vs. Avalanche Breakdown Zener breakdown is a result of the large electric field inside the depletion region that breaks electrons or holes off their covalent bonds. Avalanche breakdown is a result of electrons or holes colliding with the fixed ions inside the depletion region. 36 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 37 Lab Experiment I-V Characteristics of PN Junction Diode Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 38 Components Diode Variable Resistor Ammeter Voltmeter Voltage Supply (Signal Generator) Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 39 Diode Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 40 Variable Resistor Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 41 Ammeter Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 42 Voltmeter Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 43 Voltage Supply (Signal Generator) Compiled by NKAY STUDY NANA KWABENA  Compiled by NKAY STUDY NANA KWABENA 44 Experimental Setup Forward Bias Reverse Bias + - + - VS RV VS RV Vs = Supply Voltage Rv = Variable Resistor V = Voltmeter mA/uA = Ammeter Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 45 I-V characteristics of PN junction Diode Forward Bias Reverse Bias Test Voltmeter Ammeter Test Voltmeter Ammeter Reading Reading Reading Reading Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Diode Characteristic circuit A reading Rp R D Ev V reading A diode is a nonlinear device and typical linear circuit analysis methods do not apply! Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA …that’s all folks… …thanks for your time… Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 1 PN-Junction Diode Applications Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 2 Outline Analysis of Diode Circuit ▫ Models  Circuit model Applications of diode ▫ Rectification ▫ Half wave Rectifiers ▫ Full wave Rectifiers ▫ Centre-tap ▫ Bridge ▫ Filtration ▫ Voltage Regulators  Zener Diode Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA Diode Circuits After we have studied in detail the physics of a diode, it is time to study its behavior as a circuit element and its many applications. 3 Compiled by NKAY STUDY NANA KWABENA Compiled by NKAY STUDY NANA KWABENA 4 The Diode Models Circuit Model a) Simplified diode model b) The constant-voltage-drop model c) Zener Diode Model Compiled by NKAY STUDY N