MALVINO 7th Edition

CHAPTER 1: Introduction

SEC. 1-1 THE THREE KINDS OF FORMULASA definition is a formula invented for a new concept. A law is a formula for a relation in nature. A derivation is a formula produced with mathematics.

SEC. 1-2 APPROXIMATIONSApproximations are widely used in industry. The ideal approximation is useful for troubleshooting. The second approximation is useful for preliminary circuit calculations. Higher approximations are used with computers.

SEC. 1-3 VOLTAGE SOURCESAn ideal voltage source has no internal resistance. The second approximation of a voltage source has an internal resistance in series with the source. A stiff voltage source is defined as one whose internal resistance is less than 1/100 of the load resistance.

SEC. 1-4 CURRENT SOURCESAn ideal current source has an infinite internal resistance. The second approximation of a current source has a large internal resistance in parallel with the source. A stiff current source is defined as one whose internal resistance is more than 100 times the load resistance.

SEC. 1-5 THEVENIN’S THEOREMThe Thevenin voltage is defined as the voltage across an open load. The Thevenin resistance is defined as the resistance an ohmmeter would measure with an open load and all sources reduced to zero. Thevenin proved that a Thevenin equivalent circuit will produce the same load current as any other circuit with sources and linear resistances.

SEC. 1-6 NORTON’S THEOREMThe Norton resistance equals the Thevenin resistance. The Norton current equals the load current when the load is shorted. Norton proved that a Norton equivalent circuit produces the same load voltage as any other circuit with sources and linear resistances. Norton current equals Thevenin voltage divided by Thevenin resistance.

SEC. 1-7 TROUBLESHOOTINGThe most common troubles are shorts, opens, and intermittent troubles. A short always has zero voltage across it; the current through a short must

be calculated by examining the rest of the circuit. An open always has zero current through it; the voltage across an open must be calculated by examining the rest of the circuit. An intermittent trouble is an on-again, off-again trouble that requires patient and logical troubleshooting to isolate it.

CHAPTER 2: Semiconductors

SEC. 2-1 CONDUCTORSA neutral copper atom has only one electron in its outer orbit. Since this single electron can be easily dislodged from its atom, it is called a free electron. Copper is a good conductor because the slightest voltage causes free electrons to flow from one atom to the next.

SEC. 2-2 SEMICONDUCTORSSilicon is the most widely used semiconductor material. An isolated silicon atom has four electrons in its outer or valence orbit. The number of electrons in the valence orbit is the key to conductivity. Conductors have one valence electron, semiconductors have four valence electrons, and insulators have eight valence electrons.

SEC. 2-3 SILICON CRYSTALSEach silicon atom in a crystal has its four valence electrons plus four more electrons that are shared by the neighboring atoms. At room temperature, a pure silicon crystal has only a few thermally produced free electrons and holes. The amount of time between the creation and recombination of a free electron and a hole is called the lifetime.

SEC. 2-4 INTRINSIC SEMICONDUCTORSAn intrinsic semiconductor is a pure semiconductor. When an external voltage is applied to the intrinsic semiconductor, the free electrons flow toward the positive battery terminal and the holes flow toward the negative battery terminal.

SEC. 2-5 TWO TYPES OF FLOWTwo types of carrier flow exist in an intrinsic semiconductor. First, there is the flow of free electrons through larger orbits (conduction band). Second, there is the flow of holes through smaller orbits (valence band).

SEC. 2-6 DOPING A SEMICONDUCTORDoping increases the conductivity of a semiconductor. A doped semiconductor is called an extrinsic semiconductor. When an intrinsic semiconductor is doped with pentavalent (donor) atoms, it has more free

electrons than holes. When an intrinsic semiconductor is doped with trivalent (acceptor) atoms, it has more holes than free electrons.

SEC. 2-7 TWO TYPES OF EXTRINSIC SEMICONDUCTORSIn an n-type semiconductor the free electrons are the majority carriers, and the holes are the minority carriers. In a p-type semiconductor the holes are the majority carriers, and the free electrons are the minority carriers.

SEC. 2-8 THE UNBIASED DIODEAn unbiased diode has a depletion layer at the pn junction. The ions in this depletion layer produce a barrier potential. At room temperature, this barrier potential is approximately 0.7 V for a silicon diode and 0.3 V for a germanium diode.

SEC. 2-9 FORWARD BIASWhen an external voltage opposes the barrier potential, the diode is forwardbiased. If the applied voltage is greater than the barrier potential, the current is large. In other words, current flows easily in a forward-biased diode.

SEC. 2-10 REVERSE BIASWhen an external voltage aids the barrier potential, the diode is reverse-biased. The width of the depletion layer increases when the reverse voltage increases. The current is approximately zero.

SEC. 2-11 BREAKDOWNToo much reverse voltage will produce either avalanche or zener effect. Then, the large breakdown current destroys the diode. In general, diodes are never operated in the breakdown region. The only exception is the zener diode, a specialpurpose diode discussed in a later chapter.

SEC. 2-12 ENERGY LEVELSThe larger the orbit, the higher the energy level of an electron. If an outside force raises an electron to a higher energy level, the electron will emit energy when it falls back to its original orbit.

SEC. 2-13 THE ENERGY HILLThe barrier potential of a diode looks like an energy hill. Electrons attempting to cross the junction need to have enough energy to climb this hill. An external voltage source that forward-biases the diode gives electrons the energy required to pass through the depletion layer.

SEC. 2-14 BARRIER POTENTIAL AND TEMPERATUREWhen the junction temperature increases, the depletion layer becomes narrower and the barrier potential decreases. It will decrease approximately 2 mV for each degree Celsius increase.

SEC. 2-15 REVERSE-BIASED DIODEThere are three components of reverse current in a diode. First, there is the transient current that occurs when the reverse voltage changes. Second, there is the minority-carrier current, also called the saturation current because it is independent of the reverse voltage. Third, there is the surface-leakage current. It increases when the reverse voltage increases.

CHAPTER 3: Diode Theory

SEC. 3-1 BASIC IDEASA diode is a nonlinear device. The knee voltage, approximately 0.7 V for a silicon diode, is where the forward curve turns upward. The bulk resistance is the ohmic resistance of the p and n regions. Diodes have a maximum forward current and a power rating.

SEC. 3-2 THE IDEAL DIODEThis is the first approximation of a diode. The equivalent circuit is a switch that closes when forward biased and opens when reverse biased.

SEC. 3-3 THE SECOND APPROXIMATIONIn this approximation, we visualize a silicon diode as a switch in series with a knee voltage of 0.7 V. If the Thevenin voltage facing the diode is greater than 0.7 V, the switch closes.

SEC. 3-4 THE THIRD APPROXIMATIONWe seldom use this approximation because bulk resistance is usually small enough to ignore. In this approximation, we visualize the diode as a switch in series with a knee voltage and a bulk resistance.

SEC. 3-5 TROUBLESHOOTINGWhen you suspect that a diode is the trouble, remove it from the circuit and use an ohmmeter to measure its resistance in each direction. You should get a high resistance one way and a low resistance the other way, at least 1000:1 ratio. Remember to use a high enough resistance range when testing a diode, to avoid possible diode damage. A DMM will display 0.5–0.7 V when a diode is forward biased and an overrange indication

when it is reverse biased.

SEC. 3-6 UP-DOWN CIRCUIT ANALYSISNo calculation is required in this type of circuit analysis. All you are after is up, down, or no change. When you know beforehand how a dependent variableshould respond to an increase in an independent variable, you will be more successful at troubleshooting, analysis, and design.

SEC. 3-7 READING A DATA SHEETData sheets are useful to a circuit designer and may be useful to a repair technician for selecting a substitute device, which is sometimes required. Diode data sheets from different manufacturers contain similar information, but different symbols are used to indicate different operating conditions. Diode data sheets may list the following: breakdown voltage (VR, VRRM, VRWM, PIV, PRV, BV), maximum forward current (IF(max), IF(av), I0), forward voltage drop (VF(max), VF), and maximum reverse current IR(max), IRRM).

SEC. 3-8 HOW TO CALCULATE BULK RESISTANCEYou need two points in the forward region of the third approximation. One point can be 0.7 V with zero current. The second point comes from the data sheet at a largeforward current where both a voltage and a current are given.

SEC. 3-9 DC RESISTANCE OF A DIODEThe dc resistance equals the diode voltage divided by the diode current at some operating point. This resistance is what an ohmmeter will measure. DC resistance has limited application, aside from telling you that it is small in the forward direction and large in the reverse direction.

SEC. 3-10 LOAD LINESThe current and voltage in a diode circuit have to satisfy both the diode curve and Ohm’s law for the load resistor. These are two separate requirements that graphically translate to the intersection of the diode curve and the load line.

SEC. 3-11 SURFACE-MOUNT DIODESSurface-mount diodes are often found on modern electronics circuits boards. These diodes are small, efficient, and typically found either as an SM (surface mount) or an SOT (small outline transistor) case style.

CHAPTER 4: Diode Circuits

SEC. 4-1 THE HALF-WAVE RECTIFIERThe half-wave rectifier has a diode in series with a load resistor. The load voltage is a half-wave output. The average or dc voltage out of a half-wave rectifier equals 31.8 percent of the peak voltage.

SEC. 4-2 THE TRANSFORMERThe input transformer is usually a step-down transformer in which the voltage steps down and the current steps up. The secondary voltage equals the primary voltage divided by the turns ratio.

SEC. 4-3 THE FULL-WAVE RECTIFIERThe full-wave rectifier has a centertapped transformer with two diodes and a load resistor. The load voltage is a fullwave signal whose peak value is half the secondary voltage. The average or dc voltage out of a full-wave rectifier equals 63.6 percent of the peak voltage, and the ripple frequency equals 120 Hz instead of 60 Hz.

SEC. 4-4 THE BRIDGE RECTIFIERThe bridge rectifier has four diodes. The load voltage is a full-wave signal with a peak value equal to the secondary voltage. The average or dc voltage out of a half-wave rectifier equals 63.6 percent of the peak voltage, and the ripple frequency equals 120 Hz.

SEC. 4-5 THE CHOKE-INPUT FILTERThe choke-input filter is an LC voltage divider in which the inductive reactance is much greater than the capacitive reactance. The type of filter allows the average value of the rectified signal to pass through to the load resistor.

SEC. 4-6 THE CAPACITOR-INPUT FILTERThis type of filter allows the peak value of the rectified signal to pass through to theload resistor. With a large capacitor, the ripple is small, typically less than 10 percent of the dc voltage. The capacitorinput filter is the most widely used filter in power supplies.

SEC. 4-7 PEAK INVERSE VOLTAGE AND SURGE CURRENTThe peak inverse voltage is the maximum voltage that appears across the nonconducting diode of a rectifier circuit. This voltage must be less than the breakdown voltage of the diode. The surge current is the brief and large current that exists when the power is first turned on. It is brief and large because the filter capacitor must charge to the peak voltage during the first cycle or, at most, during the first few cycles.

SEC. 4-8 OTHER POWER-SUPPLY TOPICSReal transformers usually specify the secondary voltage at a rated load current. To calculate the primary current, you can assume that the input power equals the output power. Slow-blow fuses are typically used to protect against the surge current. The average diode current in a half-wave rectifier equals the dc load current. In a full-wave or bridge rectifier, the average current in any diode is half the dc load current. LC filters and LC filters may occasionally be used to filter the rectified output.

SEC. 4-9 TROUBLESHOOTINGSome of the measurements that can be made with a capacitor-input filter are the dc output voltage, the primary voltage, the secondary voltage, and the ripple. From these, you can usually deduce the trouble. Open diodes reduce the output voltage to zero. An open filter capacitor reduces the output to the average value of the rectified signal.

SEC. 4-10 CLIPPERS AND LIMITERSA clipper shapes the signal. It clips off positive or negative parts of the signal. The limiter or diode clamp protects sensitive circuits from too much input.

SEC. 4-11 CLAMPERSThe clamper shifts a signal positively or negatively by adding a dc voltage to the signal. The peak-to-peak detector produces a load voltage equal to the peak-to-peak value.

SEC. 4-12 VOLTAGE MULTIPLIERSThe voltage doubler is a redesign of the peak-to-peak detector. It uses rectifier diodes instead of small-signal diodes. It produces an output equal to 2 times the peak value of the rectified signal. Voltage triplers and quadruplers multiply the input peak by factors of 3 and 4. Very high voltage power supplies are the main use of voltage multipliers.

CHAPTER 5: Special Purpose Diodes

SEC. 5-1 THE ZENER DIODEThis is a special diode optimized for operation in the breakdown region. Its main use is in voltage regulators—circuits that hold the load voltage constant. Ideally, a reverse-biased zener diode is like a perfect battery. To a second approximation, it has a bulk resistance that produces a small additional voltage.

SEC. 5-2 THE LOADED ZENER REGULATORWhen a zener diode is in parallel with a load resistor, the current through the current-limiting resistor equals the sum of the zener current and the load current. The process for analyzing a zener regulator consists of finding the series current, load current, and zener current (in that order).

SEC. 5-3 SECOND APPROXIMATION OF A ZENER DIODEIn the second approximation, we visualize a zener diode as a battery of VZ and a series resistance of RZ. The current through RZ produces an additional voltage across the diode, but this voltage is usually small. You need zener resistance in order to calculate ripple reduction.

SEC. 5-4 ZENER DROP-OUT POINTA zener regulator will fail to regulate if the zener diode comes out of breakdown. The worst-case conditions occur for minimum source voltage, maximum series resistance, and minimum load resistance. For the zener regulator to work properly under all operating conditions, there must be zener current under the worst-case conditions.

SEC. 5-5 READING A DATA SHEETThe most important quantities on the data sheet of zener diodes are the zener voltage, the maximum power rating, the maximum current rating, and the tolerance. Designers also need the zener resistance, the derating factor, and a few other items.

SEC. 5-6 TROUBLESHOOTINGTroubleshooting is an art and a science. Because of this, you can learn only so much from a book. The rest has to be learned from direct experience with circuits in trouble. Because troubleshooting is an art, you have to ask “What if?” often and feel your way to a solution.

SEC. 5-7 LOAD LINESThe intersection of the load line and the zener diode graph is the Q point. When the source voltage changes, a different load line appears with a different Q point. Although the two Q points may havedifferent currents, the voltages are almost identical. This is a visual demonstration of voltage regulation.

SEC. 5-8 OPTOELECTRONIC DEVICESThe LED is widely used as an indicator on instruments, calculators, and other electronic equipment. By combining seven LEDs in a package, we get a sevensegment indicator. Another important optoelectronic device is

the optocoupler, which allows us to couple a signal between two isolated circuits.

SEC. 5-9 THE SCHOTTKY DIODEThe reverse recovery time is the time it takes a diode to shut off after it is suddenly switched from forward to reverse bias. This time may be only a few nanoseconds, but it places a limit on how high the frequency can be in a rectifier circuit. The Schottky diode is a special diode with almost zero reverse recovery time. Because of this, the Schottky diodeis useful at high frequencies where short switching times are needed.

SEC. 5-10 THE VARACTORThe width of the depletion layer increases with the reverse voltage. This is why the capacitance of a varactor can be controlled by the reverse voltage. A common application is remote tuning of radio and television sets.

SEC. 5-11 OTHER DIODESVaristors are useful as transient suppressors. Constant-current diodes hold the current, rather than the voltage, constant. Step-recovery diodes snap off and produce a step voltage that is rich in harmonics. Back diodes conduct better in the reverse direction than in the forward direction. Tunnel diodes exhibit negative resistance, which can be used in highfrequency oscillators. PIN diodes use a forward-biased control current to change its resistance in RF and microwave communication circuits.

CHAPTER 6: BJTs

SEC. 6-1 THE UNBIASED TRANSISTORA transistor has three doped regions: an emitter, a base, and a collector. A pn junction exists between the base and the emitter; this part of the transistor is called the emitter diode. Another pn junction exists between the base and the collector; this part of the transistor is called the collector diode.

SEC. 6-2 THE BIASED TRANSISTORFor normal operation, you forward bias the emitter diode and reverse bias the collector diode. Under these conditions, the emitter sends free electrons into the base. Most of these free electrons pass through the base to the collector. Because of this, the collector current approximately equals the emitter current. The base current is much smaller, typically less than 5 percent of the emitter current.

SEC. 6-3 TRANSISTOR CURRENTSThe ratio of the collector current to the base current is called the current gain, symbolized as .dc or hFE. For low-power transistors, this is typically 100 to 300. The emitter current is the largest of the three currents, the collector current is almost as large, and the base current is much smaller.

SEC. 6-4 THE CE CONNECTIONThe emitter is grounded or common in a CE circuit. The base-emitter part of a transistor acts approximately like an ordinary diode. The base-collector part acts like a current source that is equal to .dc times the base current. The transistor has an active region, a saturation region, a cutoff region, and a breakdown region. The active region is used in linear amplifiers. Saturation and cutoff are used in digital circuits.

SEC. 6-5 THE BASE CURVEThe graph of base current versus baseemitter voltage looks like the graph of an ordinary diode. Because of this, we can use any of the three diode approximations to calculate the base current. Most of the time, the ideal and the second approximation are all that is necessary.

SEC. 6-6 COLLECTOR CURVESThe four distinct operating regions of a transistor are the active region, the saturation region, the cutoff region, and the breakdown region. When it is used as an amplifier, the transistor operates in the active region. When it is used in digital circuits, the transistor usually operates in the saturation and cutoff regions. The breakdown region is avoided because the risk of transistor destruction is too high.

SEC. 6-7 TRANSISTOR APPROXIMATIONSExact answers are a waste of time in most electronics work. Almost everybody uses approximations because the answers are adequate for most applications. The ideal transistor is useful for basic troubleshooting. The third approximation is needed for precise design. The second approximation is a good compromise for both troubleshooting and design.

SEC. 6-8 READING DATA SHEETSTransistors have maximum ratings on their voltages, currents, and powers. Small-signal transistors can dissipate 1 W or less. Power transistors can dissipate more than 1 W. Temperature can change the value of the transistor characteristics. Maximum power decreases with a temperature increase. Also, current gain varies greatly with temperature.

SEC. 6-9 SURFACE-MOUNT TRANSISTORS

Surface-mount transistors (SMTs) are found in a variety of packages. A simple three-terminal gull-wing package is common. Some SMTs are packaged in styles that can dissipate more than 1 W of power. Other surface-mount devices may contain (house) multiple transistors.

SEC. 6-10 TROUBLESHOOTINGWhen troubles arise, they usually produce large changes in transistor voltages. This is why ideal analysis is usually adequate for troubleshooters. Furthermore, many troubleshooters spurn the use of calculators because it slows down their thinking. The best troubleshooters learn to mentally estimate the voltages they want to measure.

CHAPTER 7: Transistor Fundamentals

SEC. 7-1 VARIATIONS IN CURRENT GAINThe current gain of a transistor is an unpredictable quantity. Because of manufacturing tolerances, the current gain of a transistor may vary over as much as a 3.1 range when you change from one transistor to another of the same type. Changes in the temperature and the collector current produce additional variations in the dc gain.

SEC. 7-2 THE LOAD LINEThe dc load line contains all the possible dc operating points of a transistor circuit. The upper end of the load line is called saturation, and the lower end is called cutoff. The key step in finding the saturation curent is to visualize a short between the collector and the emitter. The key step to finding the cutoff voltage is to visualize an open between the collector and emitter.

SEC. 7-3 THE OPERATING POINTThe operating point of the transistor is on the dc load line. The exact location of this point is determined by the collector current and the collector-emitter voltage. With base bias, the Q point moves whenever any of the circuit values change.

SEC. 7-4 RECOGNIZING SATURATIONThe idea is to assume that the npn transistor is operating in the active region. If this leads to a contradiction (such as negative collector-emitter

voltage or collector current greater than saturation current), then you know that the transistor is operating in the saturation region. Another way to recognize saturation is by comparing the base resistance to the collector resistance. If the ratio is in the vicinity of 10 .1, the transistor is probably saturated.

SEC. 7-5 THE TRANSISTOR SWITCHBase bias tends to use the transistor as a switch. The switching action is between cutoff and saturation. This type of operation is useful in digital circits. Another name for switching circuits is two-state circuits.

SEC. 7-6 EMITTER BIASEmitter bias is virtually immune to changes in current gain. The process for analyzing emitter bias is to find the emitter voltage, emitter current, collector voltage, and collector-emitter voltage. All you need for this process is Ohm’s law.

SEC. 7-7 LED DRIVERSA base-biased LED driver uses a saturated or cutoff transistor to control the current through an LED. An emitter-biased LED driver uses the active region and cutoff to control the current through the LED.

SEC. 7-8 THE EFFECT OF SMALL CHANGESUseful to both troubleshooters and designers is the ability to predict the direction of change for a dependent voltage or current when one of the circuit values changes. When you can do this, you can better understand what happens for different troubles and can more easily analyze circuits.

SEC. 7-9 TROUBLESHOOTINGYou can use a DMM or ohmmeter to test a transistor. This is best done with the transistor disconnected from the circuit. When the transistor is in the circuit with the power on, you can measure its voltages, which are clues to possible troubles.

SEC. 7-10 MORE OPTOELECTRONIC DEVICESBecause of its .dc, the phototransistor is more sensitive to light than a photodiode. Combined with an LED, the phototransistor gives us a more sensitive optocoupler. The disadvantage with the phototransistor is that it responds more slowly to changes in light intensity than a photodiode.

CHAPTER 8: TRANSISTOR BIASING

SEC. 8-1 VOLTAGE-DIVIDER BIASThe most famous circuit based on the emitter-bias prototype is called voltagedivider bias. You can recognize it by the voltage divider in the base circuit.

SEC. 8-2 ACCURATE VDB ANALYSISThe key idea is for the base current to be much smaller than the current through the voltage divider. When this condition is satisfied, the voltage divider holds the base voltage almost constant and equal to the unloaded voltage out of the voltage divider. This produces a solid Q point under all operating conditions.

SEC. 8-3 VDB LOAD LINE AND Q POINTThe load line is drawn through saturation and cutoff. The Q point lies on the load line with the exact location determined by the biasing. Large variations in current gain have almost no effect on the Q point because this type of bias sets up a constant value of emitter current.

SEC. 8-4 TWO-SUPPLY EMITTER BIASThis design uses two power supplies: one positive and the other negative. The idea is to set up a constant value of emitter current. The circuit is a variation of the emitter-bias prototype discussed earlier.

SEC. 8-5 OTHER TYPES OF BIASThis section introduced negative feedback, a phenomenon that exists when an increase in an output quantity produces a decrease in an input quantity. It is a brilliant idea that led to voltage-divider bias. The other types of bias cannot use enough negative feedback, so they fail to attain the performance level of voltagedivider bias.

SEC. 8-6 TROUBLESHOOTINGTroubleshooting is an art. Because of this, it cannot be reduced to a set of rules. You learn troubleshooting mostly from experience.

SEC. 8-7 PNP TRANSISTORSThese pnp devices have all currents and voltages reversed from their npn counterparts. They may be used with negative power supplies; more commonly, they are used with positive power supplies in an upside-down configuration.

CHAPTER 9: AC MODELS

SEC. 9-1 BASE-BIASED AMPLIFIERGood coupling occurs when the reactance of the coupling capacitor is much smaller than the resistance at the lowest frequency of the ac source. In a basebiased amplifier, the input signal is coupled into the base. This produces an ac collector voltage. The amplified and inverted ac collector voltage is then coupled to the load resistance.

SEC. 9-2 EMITTER-BIASED AMPLIFIERGood bypassing occurs when the reactance of the coupling capacitor is much smaller than the resistance at the lowest frequency of the ac source. The bypassed point is an ac ground. With either a VDB or a TSEB amplifier, the ac signal is coupled into the base. The amplified ac signal is then coupled to the load resistance.

SEC. 9-3 SMALL-SIGNAL OPERATIONThe ac base voltage has a dc component and an ac component. These set up dc and ac components of emitter current. One way to avoid excessive distortion is to use small-signal operation. This means keeping the peak-to-peak ac emitter current less than one-tenth of the dc emitter current.

SEC. 9-4 AC BETAThe ac beta of a transistor is defined as the ac collector current divided by the ac base current. The values of the ac beta usually differ only slightly from the values of the dc beta. When troubleshooting, you can use the same value for either beta. On data sheets, hFE is equivalent to β dc, and hfe is equivalent to β .

SEC. 9-5 AC RESISTANCE OF THE EMITTER DIODEThe base-emitter voltage of a transistor has a dc component VBEQ and an ac component vbe. The ac base-emitter voltage sets up an ac emitter current of ie. The ac resistance of the emitter diode is defined as vbe divided by ie. With mathematics, we can prove that the ac resistance of the emitter diode equals 25 mV divided by dc emitter current.

SEC. 9-6 TWO TRANSISTOR MODELSAs far as ac signals are concerned, a transistor can be replaced by either of two equivalent circuits: the ð model or the T model. The ð model indicates that the input impedance of the base is β r'e.

SEC. 9-7 ANALYZING AN AMPLIFIERThe simplest way to analyze an amplifier is to split the analysis into two parts: a dc analysis and an ac analysis. In the dc analysis, the capacitors

are open. In the ac analysis, the capacitors are shorted and the dc supply points are ac grounds.

SEC. 9-8 AC QUANTITIES ON THE DATA SHEETThe h parameters are used on data sheets because they are easier to measure than r' parameters. The r. parameters are easier to use in analysis because we can use Ohm’s law and other basic ideas. The most important quantities are the data sheet are hfe and hie. They can be easily converted into >β and r'e.

CHAPTER 10: VOLTAGE AMPLIFIERS

SEC. 10-1 VOLTAGE GAINThe voltage gain of a CE amplifier equals the ac collector resistance divided by the ac resistance of the emitter diode.

SEC. 10-2 THE LOADING EFFECT OF INPUT IMPEDANCEThe input impedance of the stage includes the biasing resistors and the input impedance of the base. When the source is not stiff compared to this input impedance, the input voltage is less than the source voltage.

SEC. 10-3 MULTISTAGE AMPLIFIERSThe overall voltage gain equals the product of the individual voltage gains. The input impedance of the second stage is the load resistance on the first stage. Two CE stages produce an amplified inphase signal.

SEC. 10-4 SWAMPED AMPLIFIERBy leaving some of the emitter resistance unbypassed, we get negative feedback. This stabilizes the voltage gain, increases the input impedance, and reduces largesignal distortion.

SEC. 10-5 TWO-STAGE FEEDBACKWe can feed back the output voltage of the second collector to the first emitter through a voltage divider. This produces negative feedback, which stabilizes the voltage gain of the two-stage amplifier.

SEC. 10-6 TROUBLESHOOTINGWith single- or double-stage amplifiers, start with dc measurements. If they do not isolate the trouble, you continue with ac measurements until you have found the trouble.

CHAPTER 11: CC AND CB AMPLIFIERS

SEC. 11-1 CC AMPLIFIERA CC amplifier, better known as an emitter follower, has its collector at ac ground. The input signal drives the base and the output signal comes from the emitter. Because it is heavily swamped, an emitter follower has stable voltage gain, high input impedance, and low distortion.

SEC. 11-2 OUTPUT IMPEDANCEThe output impedance of an amplifier is the same as its Thevenin impedance. An emitter follower has a low output impedance. The current gain of a transistor transforms the source impedance driving the base to a much lower value when seen from the emitter.

SEC. 11-3 CASCADING CE AND CCWhen a low resistance load is connected to the output of a CE amplifier, it may become overloaded resulting in a very small voltage gain. A CC amplifier placed between the CE output and load will significantly reduce this effect. In this way, the CC amplifier is acting as a buffer.

SEC. 11-4 DARLINGTON CONNECTIONSTwo transistors can be connected as a Darlington pair. The emitter of the first is connected to the base of the second. This produces an overall current gain equal to the product of the individual current gains.

SEC. 11-5 VOLTAGE REGULATIONBy combining a zener diode and an emitter follower, we get a zener follower. This circuit produces regulated output voltage with large load currents. The advantage is that the zener current is much smaller than the load current. By adding a stage of voltage gain, a larger regulated output voltage can be produced.SEC. 11-6 COMMON-BASE AMPLIFIERThe CB amplifier configuration has its base at ac ground. The input signal drives the emitter and the output signal comes from the collector. Even though this circuit has no current gain, it can produce a significant voltage gain. The CB amplifier has a low input impedance and high output impedance, and is used in high-frequency applications.

CHAPTER 12: POWER AMPLIFIERS

SEC. 12-1 AMPLIFIER TERMS The classes of operation are A, B, and C. The types of coupling are capacitive, transformer, and direct. Frequency terms include audio, RF, narrowband, and wideband. Some

types of audio amplifiers are preamps and power amplifiers.

SEC. 12-2 TWO LOAD LINESEvery amplifier has a dc load line and an ac load line. To get maximum peak-topeak output, the Q point should be in the center of the ac load line.

SEC. 12-3 CLASS A OPERATIONThe power gain equals the ac output power divided by the ac input power. The power rating of a transistor must be greater than the quiescent power dissipation. The efficiency of an amplifier stage equals the ac output power divided by the dc input power, times 100 percent. The maximum efficiency of class A with a collector and load resistor is 25%. If the load resistor is the collector resistor or uses a transformer, the maximum efficiency increases to 50 percent.

SEC. 12-4 CLASS B OPERATIONMost class B amplifiers use a push-pull connection of two transistors. While one transistor conducts, the other is cut off, and vice versa. Each transistor amplifies one-half of the ac cycle. The maximum efficiency of class B is 78.5 percent.

SEC. 12-5 CLASS B PUSH-PULL EMITTER FOLLOWERClass B is more efficient than class A. In a class B push-pull emitter follower, complementary npn and pnp transistors are used. The npn transistor conducts on one half-cycle, and the pnp transistor on the other.

SEC. 12-6 BIASING CLASS B/AB AMPLIFIERSTo avoid crossover distortion, the transistors of a class B push-pull emitter follower have a small quiescent current. This is referred to as a class AB. With voltage divider bias, the Q point is unstable and may result in thermal runaway. Diode bias is preferred because it can produce a stable Q point over a large temperature range.

SEC. 12-7 CLASS B/AB DRIVERRather than capacitive couple the signal into the output stage, we can use a direct-coupled driver stage. The collector current out of the driver sets up the quiescent current through the complementary diodes.

SEC. 12-8 CLASS C OPERATIONMost class C amplifiers are tuned RF amplifiers. The input signal is negatively clamped, which produces narrow pulses of collector current. The tank circuit is tuned to the fundamental frequency, so that all higher harmonics are filtered out.

SEC. 12-9 CLASS C FORMULASThe bandwidth of a class C amplifier is inversely proportional to the Q of the circuit. The ac collector resistance includes the parallel equivalent resistance of the inductor and the load resistance.

SEC. 12-10 TRANSISTOR POWER RATINGThe power rating of a transistor decreases as the temperature increases. The data sheet of a transistor either lists a derating factor or shows a graph of the power rating versus temperature. Heat sinks can remove the heat more rapidly, producing a higher power rating.

CHAPTER 13: JFETs

SEC. 13-1 BASIC IDEASThe junction FET, abbreviated JFET, has a source, gate, and drain. The JFET has two diodes: the gate-source diode and the gate-drain diode. For normal operation, the gate-source diode is reverse biased. Then, the gate voltage controls the drain current.

SEC. 13-2 DRAIN CURVESMaximum drain current occurs when the gate-source voltage is zero. The pinchoff voltage separates the ohmic and active regions for VGS = 0. The gate-source cutoff voltage has the same magnitude as the pinchoff voltage. VGS(off) turns the JFET off.

SEC. 13-3 THE TRANSCONDUCTANCE CURVEThis is a graph of drain current versus gate-source voltage. The drain current increases more rapidly as VGS approaches zero. Because the equation for drain current contains a squared quantity, JFETs are referred to as square-law devices. The normalized transconductance curve shows that ID equals one-quarter of maximum when VGSequals half of cutoff.

SEC. 13-4 BIASING IN THE OHMIC REGIONGate bias is used to bias a JFET in the ohmic region. When it operates in the ohmic region, a JFET is equivalent to a small resistance of RDS. To ensure operation in the ohmic region, the JFET is driven into hard saturation by using VGS = 0 and ID(sat) « IDSS.

SEC. 13-5 BIASING IN THE ACTIVE REGION

When the gate voltage is much larger than VGS, voltage-divider bias can set up a stable Q point in the active region. When positive and negative supply voltages are available, two-supply source bias can be used to swamp out the variations in VGS and set up a stable Q point. When supply voltages are not large, current-source bias can be used to get a stable Q point. Self-bias is used only with small-signal amplifiers because the Q point is less stable than with the other biasing methods.

SEC. 13-6 TRANSCONDUCTANCETransconductance gm tells us how effective the gate voltage is in controlling the drain current. The quantity gm is the slope of the transconductance curve, which increases as VGS approaches zero. Data sheets may list gfs and siemens, which are equivalent to gm and mhos.

SEC. 13-7 JFET AMPLIFIERSA CS amplifier has a voltage gain of gmrd and produces an inverted output signal. One of the most important uses of a JFET amplifier is the source follower, which is often used at the front end of systems because of its high input resistance.

SEC. 13-8 THE JFET ANALOG SWITCHIn this application, the JFET acts like a switch that either transmits or blocks a small ac signal. To get this type of action, the JFET is biased into hard saturation or cutoff, depending on whether VGSis high or low. JFET shunt and series switches are used. The series type has a higher on-off ratio.

SEC. 13-9 OTHER JFET APPLICATIONSJFETs are used in multiplexers (ohmic), chopper amplifiers (ohmic), buffer amplifiers (active), voltage-controlled resistors (ohmic), AGC circuits (ohmic), cascode amplifiers (active), current sources (active), and current limiters (ohmic and active).

SEC. 13-10 READING DATA SHEETSJFETs are mainly small-signal devices because most JFETs have a power rating of less than 1 W. When reading data sheets, start with the maximum ratings. Sometimes data sheets omit the minimum VGS(off ) or other parameters. The large spread in JFET parameters justifies using ideal approximations for preliminary analysis and troubleshooting.

SEC. 13-11 JFET TESTINGJFETs can be tested using an ohmmeter or DMM on the diode test range.

Care must be taken not to exceed the JFET’s current limits. Curve tracers and circuits can be used to display a JFET’s dynamic characteristics.

CHAPTER 14: MOSFETs

SEC. 14-1 THE DEPLETIONMODE MOSFETThe depletion-mode MOSFET, abbreviated D-MOSFET, has a source, gate, and drain. The gate is insulated from the channel. Because of this, the input resistance is very high. The D-MOSFET has limited use, mainly in RF circuits.

SEC. 14-2 D-MOSFET CURVESThe drain curves for a D-MOSFET are similar to those of a JFET when the MOS device is operating in the depletion mode. Unlike JFETs, D-MOSFETs can also operate in the enhancement mode. When operating in the enhancement mode, the drain current is greater than IDSS.

SEC. 14-3 DEPLETION-MODE MOSFET AMPLIFIERSD-MOSFETs are mainly used as RF amplifiers. D-MOSFETs have good highfrequency response, generate low levels of electrical noise, and maintain high input impedance values when VGS is negative or positive. Dual-gate D-MOSFETs can be used with automatic gain control (AGC) circuits.

SEC. 14-4 THE ENHANCEMENTMODE MOSFETThe E-MOSFET is normally off. When the gate voltage equals the threshold voltage, an n-type inversion layer connects the source to the drain. When the gate voltage is much greater than the threshold voltage, the device conducts heavily. Because of the thin insulating layer, MOSFETs are easily destroyed unless you take precautions in handling them.

SEC. 14-5 THE OHMIC REGIONSince the E-MOSFET is primarily a switching device, it usually operates between cutoff and saturation. When it is biased in the ohmic region, it acts like a small resistance. IfID(sat) is less than ID(on) when VGS = VGS(on), the E-MOSFET is operating in the ohmic region.

SEC. 14-6 DIGITAL SWITCHING

Analog means that the signal changes continuously, that is, with no sudden jumps. Digital means that the signal jumps between two distinct voltage levels. Switching includes high-power circuits as well as small-signal digital circuits. Activeload switching means that one of the MOSFETs acts like a large resistor and the other like a switch.

SEC. 14-7 CMOSCMOS uses two complementary MOSFETs, in which one conducts and the other shuts off. The CMOS inverter is a basic digital circuit. CMOS devices have the advantage of very low power consumption.

SEC. 14-8 POWER FETSDiscrete E-MOSFETs can be manufactured to switch very large currents. Known as power FETS, these devices are useful in automotive controls, disk drives, converters, printers, heating, lighting, motors, and other heavy-duty applications.

SEC. 14-9 E-MOSFET AMPLIFIERSBesides their main use as power switches, E-MOSFETs find applications as amplifiers. The normally off characteristics of E-MOSFETs dictate that VGS be greater than VGS(th)when used as an amplifier. Drain-feedback bias is similar to collector feedback bias.

SEC. 14-10 MOSFET TESTINGIt is difficult to safely test MOSFET devices using an ohmmeter. If a semiconductor curve tracer is not available, MOSFETs can be tested in test circuits or by simple substitution.

CHAPTER 15: THYRISTORS

The word thyristor comes from the Greek and means "door," as in opening a door and letting something pass through it. A thyristor is a semiconductor device that uses internal feedback to produce switching action. The most important thyristors are the silicon controlled rectifier (SCR) and the triac. Like power FETs, the SCR and the triac can switch large currents on and off. Because of this, they can be used for overvoltage protection, motor controls, heaters, lighting systems, and other heavy-current loads. Insulated-gate bipolar transistors (IGBTs) are not included in the thyristor family, but are covered in this chapter as an important power-switching device.

SEC. 15-1 THE FOUR-LAYER DIODE

A thyristor is a semiconductor device that uses internal positive feedback to produce latching action. The four-layer diode, also called a Schockley diode, is the simplest thyristor. Breakover closes it, and lowcurrent drop-out opens it.

SEC. 15-2 THE SILICON CONTROLLED RECTIFIERThe silicon controlled rectifier (SCR) is the most widely used thyristor. It can switch very large currents on and off. To turn it on, we need to apply a minimum gate trigger voltage and current. To turn it off, we need to reduce the anode voltage to almost zero.

SEC. 15-3 THE SCR CROWBAROne important application of the SCR is to protect delicate and expensive loads against supply overvoltages. With an SCR crowbar, a fuse or current-limiting circuit is needed to prevent excessive current from damaging the power supply.

SEC. 15-4 SCR PHASE CONTROLAn RC circuit can vary the lag angle of gate voltage from 0 to 90°. This allows us to control the average load current. By using more advanced phase control circuits, we can vary the phase angle from 0 to 180° and have greater control over the average load current.

SEC. 15-5 BIDIRECTIONAL THYRISTORSThe diac can latch current in either direction. It is open until the voltage across it exceeds the breakover voltage. The triac is a gate-controlled device similar to an SCR. With a phase controller, a triac gives us full-wave control of the average load current.

SEC. 15-6 IGBTsThe IGBT is a hybrid device composed of a power MOSFET on the input side and a BJT on the output side. This combination produces a device with simple input gate drive requirements and low conduction losses on the output. IGBTs have an advantage over power MOSFETs in highvoltage, high-current switching applications.

SEC. 15-7 OTHER THYRISTORSThe photo-SCR latches when the incoming light is strong enough. The gate-controlled switch is designed to close with a positive trigger and open with a negative trigger. The silicon controlled switch has two input trigger gates, either of which can close or open the device. The unijunction transistor has been used to build oscillators and timing circuits.

SEC. 15-8 TROUBLESHOOTINGWhen you troubleshoot a circuit to find defective resistors, diodes, transistors, and so on, you are troubleshooting at the component level. When you are troubleshooting to find a defective functional

block, you are troubleshooting at the system level.

CHAPTER 16: FREQUENCY EFFECTS

Earlier chapters discussed amplifiers operating in their normal frequency range. Now, we want to discuss how an amplifier responds when the input frequency is outside this normal range. With ac amplifiers, the voltage gain decreases when the input frequency is too low or too high. On the other hand, dc amplifiers have voltage gain all the way down to zero frequency. It is only at higher frequencies that the voltage gain of a dc amplifier falls off. We can use decibels to describe the decrease in voltage gain and a Bode plot to graph the response of an amplifier.

SEC. 16-1 FREQUENCY RESPONSE OF AN AMPLIFIERThe frequency response is the graph of voltage gain versus input frequency. An ac amplifier has a lower and an upper cutoff frequency. A dc amplifier has only an upper cutoff frequency. Coupling and bypass capacitors produce the lower cutoff frequency. Internal transistor capacitances and stray-wiring capacitances produce the upper cutoff frequency.

SEC. 16-2 DECIBEL POWER GAINDecibel power gain is defined as 10 times the common logarithm of the power gain. When the power gain increases by a factor of 2, the decibel power gain increases by 3 dB. When the power gain increases by a factor of 10, the decibel power gain increases by 10 dB.

SEC. 16-3 DECIBEL VOLTAGE GAINDecibel voltage gain is defined as 20 times the common logarithm of the voltage gain. When the voltage gain increases by a factor of 2, the decibel voltage gain increases by 6 dB. When the voltage gain increases by a factor of 10, the decibel voltage gain increases by 20 dB. The total decibel voltage gain of cascaded stages equals the sum of the individual decibel voltage gains.

SEC. 16-4 IMPEDANCE MATCHINGIn many systems, all impedances are matched because this produces maximum power transfer. In an impedance-matched system, the decibel power gain and the decibel voltage gain are equal.

SEC. 16-5 DECIBELS ABOVE A REFERENCEBesides using decibels with power and voltage gains, we can use decibels above a reference. Two popular references are the milliwatt and the volt. Decibels with the 1 milliwatt reference are labeled dBm, and decibels with the 1 volt reference are labeled dBV.

SEC. 16-6 BODE PLOTS

An octave refers to a factor of 2 change of frequency. A decade refers to a factor of 10 change in frequency. A graph of decibel voltage gain versus frequency is called a Bode plot. Ideal Bode plots are approximations that allow us to draw the frequency response quickly and easily.

SEC. 16-7 MORE BODE PLOTSIn a lag circuit, the voltage gain breaks at the upper cutoff frequency and then rolls off at a rate of 20 dB per decade, equivalent to 6 dB per octave. We can also draw a Bode plot of phase angle versus frequency. With a lag circuit, the phase angle is between 0 and .90°.

SEC. 16-8 THE MILLER EFFECTA feedback capacitor from the output to the input of an inverting amplifier is equivalent to two capacitors. One capacitor is across the input terminals, and the other is across the output terminals. The Miller effect refers to the input capacitance being Av . 1 times the feedback capacitance.

16-9 RISETIME-BANDWIDTH RELATIONSHIPWhen a voltage step is used as the input to a dc amplifier, the risetime of the output is the time between the 10 and 90 percent points. The upper cutoff frequency equals 0.35 divided by the risetime. This gives us a quick and easy way to measure the bandwidth of a dc amplifier.

16-10 FREQUENCY ANALYSIS OF BJT STAGESThe input coupling capacitor, output coupling capacitor, and emitter bypass capacitor produce the low cutoff frequencies. The collector bypass capacitor and the input Miller capacitance produce the high cutoff frequencies. Frequency analysis of bipolar and FET stages is typically done with MultiSim or an equivalent circuit simulator.

16-11 FREQUENCY ANALYSIS OF FET STAGESThe input and output coupling capacitors of a FET stage produce the low cutoff frequencies (like a BJT stage). The drain bypass capacitances, along with the gate capacitance and input Miller capacitance, produce the high cutoff frequencies. Frequency analysis of BJT and FET stages are typically done with MultiSim or an equivalent circuit simulator.

CHAPTER 17: Differential Amplifiers

The term operational amplifier (op amp) refers to an amplifier that performs a mathematical operation. Historically, the first op amps were used in analog computers, where they did addition, subtraction, multiplication, and so on. At one time, op amps were built as discrete circuits. Now, most op amps are integrated circuits (ICs). The typical op amp is a dc amplifier with very high voltage gain, very high input

impedance, and very low output impedance. The unity-gain frequency is from 1 to more than 20 MHz, depending on the part number. An IC op amp is a complete functional block with external pins. By connecting these pins to supply voltages and a few components, we can quickly build all kinds of useful circuits. The input circuit used in most op amps is the differential amplifier. This amplifier configuration establishes many of the IC’s input characteristics. The differential amplifier may also be configured in a discrete form to be used in communications, instrumentation, and industrial control circuits. This chapter will focus on the differential amplifier used in ICs.

SEC. 17-1 THE DIFFERENTIAL AMPLIFIERA diff amp is the typical input stage of an op amp. It has no coupling or bypass capacitors. Because of this, it has no lower cutoff frequency. The input may be differential, noninverting, or inverting. The output may be single-ended or differential.

SEC. 17-2 DC ANALYSIS OF A DIFF AMPThe diff amp uses two-supply emitter bias to produce the tail current. When a diff amp is perfectly symmetrical, each emitter current is half the tail current. Ideally, the voltage across the emitter resistor equals the negative supply voltage.

SEC. 17-3 AC ANALYSIS OF A DIFF AMPBecause the tail current is ideally constant, an increase in the emitter current of one transistor produces a decrease in the emitter current of the other transistor. With a differential output, the voltage gain is RC/re.. With a single-ended output, the voltage gain is half as much.

Three important input characteristics of an op amp are the input bias current, input offset current, and input offset voltage. The input bias and offset currents produce unwanted input error voltages when they flow through the base resistors. The input offset voltage is an equivalent input error produced by differences in RC and VBE.

SEC. 17-5 COMMON-MODE GAINMost static, interference, and other kinds of electromagnetic pickup are commonmode signals. The diff amp discriminates against common-mode signals. The CMRR is the voltage gain divided by the common-mode gain. The higher the CMRR, the better.

SEC. 17-6 INTEGRATED CIRCUITSMonolithic ICs are complete circuit functions on a single chip such

as amplifiers, voltage regulators, and computer circuits. For high-power applications, thin-film, thick-film, and hybrid ICs may be used. SSI refers to fewer than 12 components, MSI to between 12 and 100 components, LSI to more than 100 components, VLSI to more than 1000 components, and ULSI to more than 1 million components.

SEC. 17-7 THE CURRENT MIRRORThe current mirror is used in ICs because it is a convenient way to create current sources and active loads. The advantages of using current mirrors are increases in voltage gain and CMRR.

SEC. 17-8 THE LOADED DIFF AMPWhen a load resistance is used with a diff amp, the best approach is to use Thevenin’s theorem. Calculate the ac output voltage vout as discussed in earlier sections. This voltage is equal to the Thevenin voltage. Use a Thevenin resistance of 2RC with a differential output and RC with a single-ended output.

CHAPTER 23: OSCILLATORS

At frequencies under 1 MHz, we can use RC oscillators to produce almost perfect sine waves. These low-frequency oscillators use op amps and RC resonant circuits to determine the frequency of oscillation. Above 1 MHz, LC oscillators are used. These high-frequency oscillators use transistors and LC resonant circuits. This chapter also discusses a popular chip called the 555 timer. It is used in many applications to produce time delays, voltage-controlled oscillators, and modulated output signals. The chapter also covers an important communications circuit called the phase-locked loop (PLL) and concludes with the popular XR-2206 function generator IC.

SEC. 23-1 THEORY OF SINUSOIDAL OSCILLATIONTo build a sinusoidal oscillator, we need to use an amplifier with positive feedback. For the oscillator to start, the loop gain must be greater than 1 when the phase shift around the loop is 0°.

SEC. 23-2 THE WIEN-BRIDGE OSCILLATORThis is the standard oscillator for low to moderate frequencies in the range of 5 Hz to 1 MHz. It produces an almost perfect sine wave. A tungsten lamp or other nonlinear resistance is used to decrease the loop gain to 1.

SEC. 23-3 OTHER RC OSCILLATORSThe twin-T oscillator uses an amplifier and RC circuits to produce the required loop gain and phase shift at the resonant frequency. It works well at one frequency but is not suitable for an adjustable frequency oscillator. The phase-shift oscillator also uses an amplifier and RC circuits to produce oscillations. An amplifier can act like a phase-shift oscillator because of the stray lead and lag circuits in each stage.

SEC. 23-4 THE COLPITTS OSCILLATORRC oscillators usually do not work well above 1 MHz because of the additional phase shift inside the amplifier. This is why LC oscillators are preferred for frequencies between 1 and 500 MHz. This frequency range is beyond the funity of most op amps, which is why a bipolar junction transistor or FET is commonly used for the amplifying device. The Colpitts oscillator is one of the most widely used LC oscillators.

SEC. 23-5 OTHER LC OSCILLATORSThe Armstrong oscillator uses a transformer to produce the feedback signal. The Hartley oscillator uses an inductive voltage divider to produce the feedback signal. The Clapp oscillator has a small series capacitor in the inductive branch of the resonant circuit. This reduces the effect that stray capacitances have on the resonant frequency.

SEC. 23-6 QUARTZ CRYSTALSSome crystals exhibit the piezoelectric effect. Because of this effect, a vibrating crystal acts like an LC resonant circuit with an extremely high Q. Quartz is the most important crystal producing the piezoelectric effect. It is used in crystal oscillators, in which a precise and reliable frequency is needed.

SEC. 23-7 THE 555 TIMERThe 555 timer contains two comparators, an RS flip-flop, and an npn transistor. It has an upper and lower trip point. When used in the monostable mode, the input triggers must fall below LTP to start the action. When the capacitor voltage slightly exceeds UTP, the discharge transistor turns on to discharge the capacitor.

SEC. 23-8 ASTABLE OPERATION OF THE 555 TIMERWhen used in the astable mode, the 555 timer produces a rectangular output whose duty cycle can be set between 50 and 100 percent. The capacitor charges between VCC/3 and 2VCC/3. When a control voltage is used, it changes UTP to Vcon. This control voltage determines the frequency.

SEC. 23-9 555 CIRCUITSThe 555 timer can be used to create time delays, alarms, and ramp outputs. It can also be used to build a pulse-width modulator by applying a modulating signal to the control input and a train of negative-going triggers to the trigger input. The 555 time can also be used to build a pulse-position modulator by applying a modulating signal to the control input when the timer is in the astable mode.

SEC. 23-10 THE PHASE-LOCKED LOOPA PLL contains a phase detector, a dc amplifier, a low-pass filter, and a VCO. The phase detector produces a control voltage that is proportional to the phase difference between its two input signals. The amplified and filtered control voltage then changes the frequency of the VCO as needed to lock on to the input signal.

SEC. 23-11 FUNCTION GENERATOR ICSFunction generator ICs have the ability to produce sine, square, triangle, pulse, and sawtooth waveforms. By connecting external resistors and capacitors, the output waveforms can be made to vary in frequency and amplitude. Special functions including AM/FM generation, voltage-to-frequency conversion, and frequency-shift keying can also be performed by these ICs.

CHAPTER 24: REGULATED POWER SUPPLIES

With a zener diode, we can build simple voltage regulators. Now, we want to discuss the use of negative feedback to improve voltage regulation. The discussion begins with linear regulators, the kind in which the regulating device is operating in the linear region. We will discuss two types of linear regulators: the shunt type and the series type. This chapter concludes with switching regulators, the type in which the regulating device switches on and off to improve the power efficiency.

SEC. 24-1 SUPPLY CHARACTERISTICSLoad regulation indicates how much the output voltage changes when the load current changes. Line regulation indicates how much the load voltage changes when the line voltage changes. The output resistance determines the load regulation.

SEC. 24-2 SHUNT REGULATORSThe zener regulator is the simplest example of a shunt regulator. By adding transistors and an op amp, we can build a shunt regulator that has excellent line and load regulation. The main disadvantage of a shunt regulator is its low efficiency, caused by power losses in the series resistor and shunt transistor.

SEC. 24-3 SERIES REGULATORSBy using a pass transistor instead of a series resistor, we can build series regulators with higher efficiencies than shunt regulators. The zener follower is the simplest example of a series regulator. By adding transistors and an op amp, we can build series regulators with excellent line and load regulation, plus current limiting.

SEC. 24-4 MONOLITHIC LINEAR REGULATORSIC voltage regulators have one of the following voltages: fixed positive, fixed negative, or adjustable. IC regulators are also classified as standard, low-power, and low-dropout. The LM78XX series is a standard line of fixed regulators with output voltages from 5 to 24 V.

SEC. 24-5 CURRENT BOOSTERSTo increase the regulated load current of an IC regulator such as a 78XX device, we can use an outboard transistor to carry most of the current above 1 A. By adding another transistor, we can have shortcircuit protection.

SEC. 24-6 DC-TO-DC CONVERTERSWhen we want to convert an input dc voltage to an output dc voltage of another value, a dc-to-dc converter is useful. Unregulated dc-to-dc converters have an oscillator whose output voltage is proportional to the input voltage. Typically, a push-pull arrangement of transistors and a transformer can step this voltage up or down. Then, it is rectified and filtered to get an output voltage different from the input voltage.

SEC. 24-7 SWITCHING REGULATORSA switching regulator is a dc-to-dc converter that uses pulse-width modulation to regulate the output voltage. By switching the pass transistor on and off, the switching regulator can attain efficiencies from 70 to 95 percent. The basic topologies are the buck (stepdown), boost (step-up), and buck-boost (inverting). This type of regulator is very popular in computer and portable electronic systems.

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SEC. 18-1 INTRODUCTION TO OP AMPSA typical op amp has a noninverting input, an inverting input, and a singleended output. An ideal op amp has infinite open-loop voltage gain, infinite input resistance, and zero output impedance. It is a perfect amplifier, a voltage-controlled voltage source (VCVS).

SEC. 18-2 THE 741 OP AMPThe 741 is a standard op amp that is widely used. It includes an internal compensating capacitor to prevent oscillations. With a large load resistance, the output signal can swing to within 1 or 2 V of either supply. With small load resistances, MPP is limited by the shortcircuit current. The slew rate is the maximum speed at which the output voltage can change when driven by a step input. The power bandwidth is directly proportional to slew rate and inversely proportional to the peak output voltage.

SEC. 18-3 THE INVERTING AMPLIFIERThe inverting amplifier is the most basic op-amp circuit. It uses negative feedback to stabilize the closed-loop voltage gain. The inverting input is a virtual ground because it is a short for voltage but an open for current. The closed-loop voltage gain equals the feedback resistance divided by the input resistance. The closed-loop bandwidth equals the unitygain frequency divided by the closed-loop voltage gain.

SEC. 18-4 THE NONINVERTING AMPLIFIERThe noninverting amplifier is another basic op-amp circuit. It uses negative feedback to stabilize the closed-loop voltage gain. A virtual short is between the noninverting input and the inverting input. The closed-loop voltage gain equals Rf/R1 . 1. The closed-loop bandwidth equals the unity-gain frequency divided by the closed-loop voltage gain.

SEC. 18-5 TWO OP-AMP APPLICATIONSThe summing amplifier has two or more inputs and one output. Each input is amplified by its channel gain. The output is the sum of the amplified inputs. If all channel gains equal unity, the output equals the sum of the inputs. In a mixer, a summing amplifier can amplify and combine audio signals. A voltage follower has a closed-loop voltage gain of unity and a bandwidth of funity. The circuit is useful as an interface between a high-impedance source and a lowimpedance load.

SEC. 18-6 LINEAR ICSOp amps represent about a third of all linear ICs. A wide variety of op amps exists for almost any application. Some have very low input offsets, other have high bandwidths and slew rates, and others have low drifts. Dual and quad op amps are available. Even high-power op amps exist that can produce large load power. Other linear ICs include audio and video amplifiers, RF and IF amplifiers, and voltage regulators.

CHAPTER 23: OSCILLATORS

At frequencies under 1 MHz, we can use RC oscillators to produce almost perfect sine waves. These low-frequency oscillators use op amps and RC resonant circuits to determine the frequency of oscillation. Above 1 MHz, LC oscillators are used. These high-frequency oscillators use transistors and LC resonant circuits. This chapter also discusses a popular chip called the 555 timer. It is used in many applications to produce time delays, voltage-controlled oscillators, and modulated output signals. The chapter also covers an important communications circuit called the phase-locked loop (PLL) and concludes with the popular XR-2206 function generator IC.

SEC. 23-1 THEORY OF SINUSOIDAL OSCILLATIONTo build a sinusoidal oscillator, we need to use an amplifier with positive feedback. For the oscillator to start, the loop gain must be greater than 1 when the phase shift around the loop is 0°.

SEC. 23-2 THE WIEN-BRIDGE OSCILLATORThis is the standard oscillator for low to moderate frequencies in the range of 5 Hz to 1 MHz. It produces an almost perfect sine wave. A tungsten lamp or other nonlinear resistance is used to decrease the loop gain to 1.

SEC. 23-3 OTHER RC OSCILLATORSThe twin-T oscillator uses an amplifier and RC circuits to produce the required loop gain and phase shift at the resonant frequency. It works well at one frequency but is not suitable for an adjustable frequency oscillator. The phase-shift oscillator also uses an amplifier and RC circuits to produce oscillations. An amplifier can act like a phase-shift oscillator because of the stray lead and lag circuits in each stage.

SEC. 23-4 THE COLPITTS OSCILLATORRC oscillators usually do not work well above 1 MHz because of the additional phase shift inside the amplifier. This is why LC oscillators are preferred for frequencies between 1 and 500 MHz. This frequency range is beyond the funity of most op amps, which is why a bipolar junction transistor or FET is commonly used for the amplifying device. The Colpitts oscillator is one of the most widely used LC oscillators.

SEC. 23-5 OTHER LC OSCILLATORSThe Armstrong oscillator uses a transformer to produce the feedback signal. The Hartley oscillator uses an inductive voltage divider to produce the feedback signal. The Clapp oscillator has a small series capacitor in the inductive branch of the resonant circuit. This reduces the effect that stray capacitances have on the resonant frequency.

SEC. 23-6 QUARTZ CRYSTALSSome crystals exhibit the piezoelectric effect. Because of this effect, a vibrating crystal acts like an LC resonant circuit with an extremely high Q. Quartz is the most important crystal producing the piezoelectric effect. It is used in crystal oscillators, in which a precise and reliable frequency is needed.

SEC. 23-7 THE 555 TIMERThe 555 timer contains two comparators, an RS flip-flop, and an npn transistor. It has an upper and lower trip point. When used in the monostable mode, the input triggers must fall below LTP to start the action. When the capacitor voltage slightly exceeds UTP, the discharge transistor turns on to discharge the capacitor.

SEC. 23-8 ASTABLE OPERATION OF THE 555 TIMERWhen used in the astable mode, the 555 timer produces a rectangular output whose duty cycle can be set between 50 and 100 percent. The capacitor charges between VCC/3 and 2VCC/3. When a control voltage is used, it changes UTP to Vcon. This control voltage determines the frequency.

SEC. 23-9 555 CIRCUITSThe 555 timer can be used to create time delays, alarms, and ramp outputs. It can also be used to build a pulse-width modulator by applying a modulating signal to the control input and a train of negative-going triggers to the trigger input. The 555 time can also be used to build a pulse-position modulator by applying a modulating signal to the control input when the timer is in the astable mode.

SEC. 23-10 THE PHASE-LOCKED LOOPA PLL contains a phase detector, a dc amplifier, a low-pass filter, and a VCO. The phase detector produces a control voltage that is proportional to the phase difference between its two input signals. The amplified and filtered control voltage then changes the frequency of the VCO as needed to lock on to the input signal.

SEC. 23-11 FUNCTION GENERATOR ICSFunction generator ICs have the ability to produce sine, square, triangle, pulse, and sawtooth waveforms. By connecting external resistors and capacitors, the output waveforms can be made to vary in frequency and amplitude. Special functions including AM/FM generation, voltage-to-frequency conversion, and frequency-shift keying can also be performed by these ICs.

CHAPTER 24: REGULATED POWER SUPPLIES

With a zener diode, we can build simple voltage regulators. Now, we want to discuss the use of negative feedback to improve voltage regulation. The discussion begins with linear regulators, the kind in which the regulating device is operating in the linear region. We will discuss two types of linear regulators: the shunt type and the series type. This chapter concludes with switching regulators, the type in which the regulating device switches on and off to improve the power efficiency.

SEC. 24-1 SUPPLY CHARACTERISTICSLoad regulation indicates how much the output voltage changes when the load current changes. Line regulation indicates how much the load voltage changes when the line voltage changes. The output resistance determines the load regulation.

SEC. 24-2 SHUNT REGULATORSThe zener regulator is the simplest example of a shunt regulator. By adding transistors and an op amp, we can build a shunt regulator that has excellent line and load regulation. The main disadvantage of a shunt regulator is its low efficiency, caused by power losses in the series resistor and shunt transistor.

SEC. 24-3 SERIES REGULATORSBy using a pass transistor instead of a series resistor, we can build series regulators with higher efficiencies than shunt regulators. The zener follower is the simplest example of a series regulator. By adding transistors and an op amp, we can build series regulators with excellent line and load regulation, plus current limiting.

SEC. 24-4 MONOLITHIC LINEAR REGULATORSIC voltage regulators have one of the following voltages: fixed positive, fixed negative, or adjustable. IC regulators are also classified as standard, low-power, and low-dropout. The LM78XX series is a standard line of fixed regulators with output voltages from 5 to 24 V.

SEC. 24-5 CURRENT BOOSTERSTo increase the regulated load current of an IC regulator such as a 78XX device, we can use an outboard transistor to carry most of the current above 1 A. By adding another transistor, we can have shortcircuit protection.

SEC. 24-6 DC-TO-DC CONVERTERSWhen we want to convert an input dc voltage to an output dc voltage of another value, a dc-to-dc converter is useful. Unregulated dc-to-dc converters have an oscillator whose output voltage is proportional to the input voltage. Typically, a push-pull arrangement of transistors and a transformer can step this voltage up or down. Then, it is rectified and filtered to get an output voltage different from the input voltage.

SEC. 24-7 SWITCHING REGULATORSA switching regulator is a dc-to-dc converter that uses pulse-width modulation to regulate the output voltage. By switching the pass transistor on and off, the switching regulator can attain efficiencies from 70 to 95 percent. The basic topologies are the buck (stepdown), boost (step-up), and buck-boost (inverting). This type of regulator is very popular in computer and portable electronic systems.

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