Chas Keithan

Electronics Notes

Chapter 1

1) An ideal voltage source has zero internal resistance.

2) A real voltage source has a small internal resistance.

3) If a load resistance is 100 Ω, a stiff voltage source has a resistance of less than 1 Ω.

4) An ideal current source has infinite internal resistance.

5) A real current source has a large internal resistance.

6) If a load resistance is 100 Ω, a stiff current source has a resistance of more than 10 kΩ.

7) The Thevenin voltage is the same as the open-load voltage.

8) The Thevenin resistance is equal in value to the internal resistance of a Norton circuit.

9) To get the Thevenin voltage, you have to open the load resistor.

10) To get the Norton current, you have to short the load resistor.

11) The Norton current is sometimes called the shorted-load current.

12) A solder bridge may produce a short.

13) A cold-solder joint usually produces an open.

14) An open resistor has zero current through it.

15) A shorted resistor has zero voltage across it.

16) An ideal voltage source and an internal resistance are examples of the second approximation.

17) Treating a connecting wire as a conductor with zero resistance is an example of the ideal approximation.

18) The voltage out of an ideal voltage source is constant.

19) The current out of an ideal current source is constant.

20) Thevenin’s theorem replaces a complicated circuit facing a load by an ideal voltage source and series resistor.

21) Norton’s theorem replaces a complicated circuit facing a load by an ideal current source and parallel resistor.

22) One way to short a device is with a solder bridge.

23) Derivations are produced by mathematics.

Chapter 2

1) The nucleus of a copper atom contains how many protons? 29.

2) The net charge of a neutral copper atom is 0.

3) Assume the valence electron is removed from a copper atom. The net charge of the atom becomes + 1.

4) The valence electron of a copper atom experiences what kind of attraction toward the nucleus? Weak.

5) How many valence electrons does a silicon atom have? 4.

6) Which is the most widely used semiconductor? Silicon.

7) How many protons does the nucleus of a silicon atom contain? 14.

8) Silicon atoms combine into an orderly pattern called a crystal.

9) An intrinsic semiconductor has some holes in it at room temperature. What causes these holes? Thermal energy.

10) When an electron is moved to a higher orbit level, its energy level with respect to the nucleus increases.

11) The merging of a free electron and a hole is called recombination.

12) At room temperature an intrinsic silicon crystal acts approximately like an insulator.

13) The amount of time between the creation of a hole and its disappearance is called lifetime.

14) The valence electron of a conductor can also be called a free electron.

15) A conductor has how many types of flow? 1.

16) A semiconductor has how many types of flow? 2.

17) When a voltage is applied to a semiconductor, holes will flow none of the above.

18) For semiconductor material, its valence orbit is saturated when it contains 8 electrons.

19) In an intrinsic semiconductor, the number of holes equals the number of free electrons.

20) Absolute zero temperature equals -273°C.

21) At absolute zero temperature an intrinsic semiconductor has no holes or free electrons.

22) At room temperature an intrinsic semiconductor has a few free electrons and holes.

23) The number of free electrons and holes in an intrinsic semiconductor decreases when the temperature decreases.

24) The flow of valence electrons to the right means that holes are flowing to the left.

25) Holes act like positive charges.

26) Trivalent atoms have how many valence electrons? 3.

27) An acceptor atom has how many valence electrons? 3.

28) If you wanted to produce an n-type semiconductor, which of these would you use? Donor atoms.

29) Electrons are the minority carriers in which type of semiconductor? P-type.

30) How many free electrons does a p-type semiconductor contain? Only those produced by thermal energy.

31) Silver is the best conductor. How many valence electrons do you think it has? 1.

32) Suppose an intrinsic semiconductor has 1 billion free electrons at room temperature. If the temperature drops to 0°C, how many holes are there? Fewer than 1 billion.

33) An external voltage source is applied to a p-type semiconductor. If the left end of the crystal is positive, which way dot the majority carriers flow? Right.

34) Which of the following doesn’t fit in the group? Conductor.

35) Which of the following is approximately equal t room temperature? 25°C.

36) How many electrons are there in the valence orbit of a silicon atom within a crystal? 8.

37) Negative ions are atoms that have gained an electron.

38) Which of the following describes an n-type semiconductor? Neutral.

39) A p-type semiconductor contains holes and negative ions.

40) Which of the following describes a p-type semiconductor? Neutral.

41) As compared to a germanium diode, a silicon diode’s reverse saturation current is lower.

42) What causes the depletion layer? Recombination.

43) What is the barrier potential of a silicon diode at room temperature? .7V.

44) When comparing the energy gap of germanium and silicon atoms, a silicon atom’s energy gap is higher.

45) In a silicon diode the reverse current is usually very small.

46) While maintaining a constant temperature, a silicon diode has its reverse-bias voltage increased. The diode’s saturation current will remain the same.

47) The voltage where avalanche occurs is called the breakdown voltage.

48) The energy hill of diode’s pn junction will decrease when the diode is forward biased.

49) When the reverse voltage decreases from 10 to 5 V, the depletion layer becomes smaller.

50) When a diode is forward-biased, the recombination of electrons and holes may produce heat, light and radiation.

51) A reverse voltage of 10 V is across a diode. What is the voltage across the depletion layer? 10 V.

52) The energy gap in a silicon atom is the distance between the valence band and the conduction band.

53) The reverse saturation current doubles when the junction temperature increases 10°C.

54) The surface-leakage current doubles when the reverse voltage increases 100%.

Chapter 3

1) When the graph of current versus voltage is a straight line, the device is referred to as linear.

2) What kind of device is a resistor? Linear.

3) What kind of device is a diode? Nonlinear.

4) How is a non-conducting diode biased? Reverse.

5) When the diode current is large, the bias is forward.

6) The knee voltage of a diode is approximately equal to the barrier potential.

7) The reverse current consists of minority-carrier current and surface-leakage current.

8) How much voltage is there across the second approximation of a silicon diode when it is forward biased? .7 V.

9) How much current is there through the second approximation of a silicon diode when it is reverse biased? 0.

10) How much forward diode voltage is there with the ideal-diode approximation? 0.

11) The bulk resistance of a 1N4001 is .23 Ω.

12) If the bulk resistance is zero, the graph above the knee becomes vertical.

13) The ideal diode is usually adequate when troubleshooting.

14) The second approximation works well when troubleshooting, load resistance is high, and/or source voltage is high.

15) The only time you have to use the third approximation is when load resistance is low.

Chapter 4

1) If N1 / N2 = 4, and the primary voltage is 120 V, what is the secondary voltage? 30 V.

2) In a step-down transformer, which is larger? Primary voltage.

3) A transformer has a turns ratio of 2:1. What is the peak secondary voltage if 115 V rms is applied to the primary winding? 81.3 V.

4) With a half-wave rectified voltage across the load resistor, load current flows for what part of a cycle? 180°.

5) Suppose line voltage may be as low as 105 V rms or as high as 125 V rms in a half-wave rectifier. With a 5:1 step-down transformer, the minimum peak load voltage is closest to 29.7 V.

6) The voltage out of a bridge rectifier is a full-wave signal.

7) If the line voltage is 115 V rms, a turns ratio of 5:1 means the rms secondary voltage is closest to 23 V.

8) What is the peak load voltage in a full-wave rectifier if the secondary voltage is 20 V rms? 14.1 V.

9) We want a peak load voltage of 40 V out of a bridge rectifier. What is the approximate rms value of secondary voltage? 28.3 V.

10) With a full-wave rectified voltage across the load resistor, load current flows for what part of a cycle? 360°.

11) What is the peak load voltage out of a bridge rectifier for a secondary voltage of 12.6 V rms? (Use second approximation.) 16.4 V.

12) If line frequency is 60 Hz, the output frequency of a half-wave rectifier is 60 Hz.

13) If line frequency is 60 Hz, the output frequency of a bridge rectifier is 120 Hz.

14) With the same secondary voltage and filter, which has the most ripple? Half-wave rectifier.

15) With the same secondary voltage and filter, which produces the least load voltage? Full-wave rectifier.

16) If the filtered load current is 10 mA, which of the following has a diode current of 10 mA? Half-wave rectifier.

17) If the load current is 5 mA and the filter capacitance is 1000 μF, what is the peak-to-peak ripple out of a bridge rectifier? 41.7 mV.

18) The diodes in a bridge rectifier each have a maximum dc current rating of 2 A. This means the dc load current can have a maximum value of 4 A.

19) What is the PIV across each diode of a bridge rectifier with a secondary voltage of 20 V rms? 28.3 V.

20) If the secondary voltage increases in a bridge rectifier with a capacitor-input filter, the load voltage will increase.

21) If the filter capacitance is increased, the ripple will decrease.

22) A circuit that removes positive or negative parts of a waveform is called a clipper.

23) A circuit that adds a positive or negative dc voltage to an input sine-wave is called a clamper.

24) For a clamper circuit to operate properly, its RLC time constant should be > 100 times the period T of the signal.

25) Voltage multipliers are circuits best used to produce high voltage and low current.

Chapter 5

1) What is true about the breakdown voltage in a zener diode? It is approximately constant.

2) Which of these is the best description of a zener diode? It is a constant-voltage device.

3) A zener diode has a constant voltage in the breakdown region.

4) The voltage across the zener resistance is usually small.

5) If the series resistance increases in an unloaded zener regulator, the zener current decreases.

6) In the second approximation, the total voltage across the zener diode is the sum of the breakdown voltage and the voltage across the zener resistance.

7) The load voltage is approximately constant when a zener diode is operating in the breakdown region.

8) In a loaded zener regulator, which in the largest current? Series current.

9) If the load resistance increases in a zener regulator, the zener current increases.

10) If the load resistance decreases in a zener regulator, the series current stays the same.

11) When the source voltage increases in a zener regulator, which of these currents remains approximately constant? Load current.

12) If the zener diode in a zener regulator is connected with the wrong polarity, the load voltage will be closest to .7 V.

13) When a zener diode is operating above its power-rated temperature you must decrease its power rating.

14) Which of the following will not indicate a zener diode’s breakdown voltage? DMM.

15) At high frequencies, ordinary diodes don’t work properly because of charge storage.

16) The capacitance of a varactor diode increases when the reverse voltage across it decreases.

17) Breakdown does not destroy a zener diode, provided the zener current is less than the maximum zener current rating.

18) As compared to a silicon rectifier diode, an LED has a higher forward voltage and lower breakdown voltage.

19) To display the digit 0 in a seven-segment indicator, G must be off.

20) A photodiode is normally reverse biased.

21) When the light decreases, the reverse minority-carrier current in a photodiode decreases.

22) The device associated with voltage-controlled capacitance is a varactor diode.

23) If the depletion layer width decreases, the capacitance increases.

24) When the reverse voltage decreases, the capacitance increases.

25) The varactor is usually reverse biased.

26) The device to use for rectifying a weak ac signal is a back diode.

27) Which of the following has a negative-resistance region? Tunnel diode.

28) A blown-fuse indicator uses a light-emitting diode.

29) To isolate an output circuit, which is the device to use? Optocoupler.

30) The diode with a forward voltage drop of approximately .25 V is the Schottky diode.

31) For typical operation, you need to use reverse bias with a zener diode, photodiode and/or varactor.

32) AS the forward current through a PIN diode decreases, its resistance increases.

Chapter 6

1) A transistor has how many pn junctions? 2.

2) What is one important thing transistors do? Amplify weak signals.

3) Who invented the first junction transistor? Schockley.

4) In an npn transistor, the majority carriers in the emitter are free electrons.

5) The barrier potential across each silicon depletion layer is .7 V.

6) The emitter diode is usually forward biased.

7) For normal operation of the transistor, the collector diode has to be reverse biased.

8) The base of an npn transistor is thin and lightly doped.

9) Most of the electrons in the base of an npn transistor flow into the collector.

10) Most of the electrons in the base of an npn transistor do not recombine because they have a long lifetime.

11) Most of the electrons that flow through the base will flow into the collector.

12) The beta of a transistor is the ratio of the collector current to base current.

13) Increasing the collector supply voltage will increase none of the above.

14) The fact that there are many free electrons in a transistor emitter region means the emitter is heavily doped.

15) In a normally biased npn transistor, the electrons in the emitter have enough energy to overcome the barrier potential of the base-emitter junction.

16) In a pnp transistor, the major carriers in the emitter are holes.

17) What is the most important fact about the collector current? It approximately equals the emitter current.

18) If the current gain is 100 and the collector current is 10 mA, the base current is 100 μA.

19) The base-emitter voltage is usually less than the collector supply voltage.

20) The collector-emitter voltage is usually less than the collector supply voltage.

21) The power dissipated by a transistor approximately equals the collector current times collector-emitter voltage.

22) A small collector current with zero base current is caused by the leakage current of the collector diode.

23) A transistor acts like a diode and a current source.

24) If the base current is 100 mA and the current gain is 30, the emitter current is 3.1 A.

25) The base-emitter voltage of an ideal transistor is 0.

26) If you recalculate the collector-emitter voltage with the second approximation, the answer will usually be larger than the ideal value.

27) In the active region, the collector current is not changed significantly by collector resistance.

28) The base-emitter voltage of the second approximation is .7 V.

29) If the base resistor is open, what is the collector current? 0.

30) When comparing the power dissipation of a 2N3904 transistor to the PZT3904 surface-mount version, the 2N3904 can handle less power.

Chapter 7

1) The current gain of a transistor is defined as the ratio of the collector current to the base current.

2) The graph of current gain versus collector current indicates that the current gain varies slightly.

3) When the collector current increases, what does the current gain do? Any of the above.

4) As the temperature increases, the current gain can be any of the above.

5) When the base resistor increases, the collector voltage will probably increase.

6) If the base resistor is very small, the transistor will operate in the saturation region.

7) Ignoring the bulk resistance of the collector diode, the collector-emitter saturation voltage is 0.

8) Three different Q points are shown on a load line. The upper Q pint represents the maximum current gain.

9) If a transistor operates at the middle of the load line, a decrease in the base resistance will move the Q point up.

10) If a transistor operates at the middle of the load line, a decrease in the current gain will move the Q point down.

11) If the base supply voltage increases, the Q pint moves up.

12) Suppose the base resistor is open. The Q point will be at the lower end of the load line.

13) If the base supply voltage is disconnected, the collector-emitter voltage will equal collector supply voltage.

14) If the base resistor has a zero resistance, the transistor will probably be destroyed.

15) If the collector resistor opens in a base-biased circuit, the load line will become horizontal.

16) The collector current is 1.5 mA. If the current gain is 50, the base current is 30 μA.

17) The base current is 50 μA. If the current gain is 100, the collector current is closest in value to 5 mA.

18) When the Q point moves along the load line, VCE decreases when the collector current increases.

19) When there is no base current in a transistor switch, the output voltage from the transistor is high.

20) A circuit with a fixed emitter current is called emitter bias.

21) The first step in analyzing emitter-biased circuits is to find the emitter voltage.

22) If the current gain is unknown in an emitter-biased circuit, you cannot calculate the base current.

23) If the emitter resistor is open, the collector voltage is high.

24) If the collector resistor is open, the collector voltage is low.

25) When the current gain increases from 50 to 300 in an emitter-biased circuit, the collector current remains almost the same.

26) If the emitter resistance increases, the collector voltage increases.

27) If the emitter resistance decreases, the Q point moves up.

28) When using a DMM to test a transistor, an approximate reading of .7 V will be found with how many polarity connections? 2.

29) What DMM polarity connection is needed on an npn transistor’s base to get a .7 V reading? Positive.

30) When testing an npn transistor using an ohmmeter, the collector-emitter resistance will be low when the transistor is defective.

31) The major advantage of a phototransistor as compared to a photodiode is its increased sensitivity.

Chapter 8

1) For the emitter bias, the voltage across the emitter resistor is the same as the voltage between the emitter and the ground.

2) For emitter bias, the voltage ate the emitter is .7 V less than the base voltage.

3) With voltage-divider bias, the bas voltage is less than the base supply voltage.

4) VDB is noted for its stable Q point.

5) With VDB, an increase in collector resistance will decrease the collector voltage.

6) VDB has a stable Q point like emitter bias.

7) VDB needs only one supply.

8) VDB normally operates in the active region.

9) The collector voltage of a VDB circuit is not sensitive to changes in the current gain.

10) If the emitter resistance decreases in a VDG circuit, the collector voltage decreases.

11) Base bias is associated with switching circuits.

12) If the emitter resistance is reduced by one-half in a VDB circuit, the collector current will double.

13) If the collector resistance decreases in a VDB circuit, the collector voltage will increase.

14) The Q point of a VDB circuit is almost totally insensitive to changes in current gain.

15) The base voltage of two-supply emitter bias (TSEB) is near 0 V.

16) If the emitter resistance doubles with TSEB, the collector current will drop in half.

17) If a splash of solder shorts the collector resistor of TSEB, the collector voltage will equal the collector supply voltage.

18) If the emitter resistance decreases with TSEB, the collector voltage will decrease.

19) If the base resistor opens with TSEB, the collector voltage will equal the collector supply voltage.

20) In TSEB, the base current must be very small.

21) The Q point of TSEB does not depend on the current gain.

22) The majority carriers in the emitter of a pnp transistor are holes.

23) The current gain of a pnp transistor is the ratio of collector current to base current.

24) Which is the largest current in a pnp transistor? Emitter current.

25) The currents of a pnp transistor are opposite npn currents.

26) With pnp voltage-divider bias, you must use resistors.

27) With a TSEB pnp circuit using a negative VCC supply, the emitter voltage is .7 V higher than the base voltage.

28) In a well-designed VDB circuit, the base current is much smaller than the voltage divider current.

29) In a VDB circuit, the base input resistance RIN is equal to βdc RE.

30) In a TSEB circuit, the base voltage is approximately zero when RB < .01 βdc RE.

Chapter 9

1) For dc, the current in a coupling circuit is 0.

2) The current in a coupling circuit for high frequencies is maximum.

3) A coupling capacitor is a dc open and an ac short.

4) In a bypass circuit, the top of a capacitor is an ac ground.

5) The capacitor that produces an ac ground is called a bypass capacitor.

6) The capacitors of a CE amplifier appear to be shorted to ac.

7) Reducing all dc sources to zero is one of the steps in getting the ac equivalent circuit.

8) The ac equivalent circuit is derived from the original circuit by shorting all capacitors.

9) When the ac base voltage is too large, the ac emitter current is distorted.

10) In a CE amplifier with a large input signal, the positive half cycle of the ac emitter current is larger than the negative half cycle.

11) AC emitter resistance equals 25 mV divided by the dc emitter current.

12) To reduce the distortion in a CE amplifier, reduce the ac base voltage.

13) If the ac voltage across the emitter diode is 1 mV and the ac emitter current is 100 μA, the ac resistance of the emitter diode is 10 Ω.

14) A graph of ac emitter current versus ac base-emitter voltage applies to the emitter diode.

15) The output voltage of a CE amplifier is amplified, inverted and 180° out of phase with the input.

16) The emitter of a CE amplifier has no ac voltage because of the bypass capacitor.

17) The voltage across the load resistor of a capacitor-coupled CE amplifier is ac only.

18) The ac collector current is approximately equal to the ac emitter current.

19) The ac emitter current times the ac emitter resistance equals the ac base voltage.

20) The ac collector current equals the ac base current times the ac current gain.

21) When the emitter resistance RE doubles, the ac emitter resistance increases.

Chapter 10

1) The emitter is at ac ground in a CE stage.

2) The output voltage of an emitter-bypassed CE stage is usually dependent on re’.

3) The voltage gain equals the output voltage divided by the input voltage.

4) The input impedance of the base decreases when β increases.

5) Voltage gain is directly proportional to ac collector resistance.

6) Compared to the ac resistance the emitter diode, the feedback resistance of a swamped amplifier should be large.

7) Compared to a CE stage, a swamped amplifier has an input impedance that is larger.

8) To reduce the distortion of an amplified signal, you can increase the emitter feedback resistance.

9) The emitter of a swamped amplifier has an ac voltage.

10) A swamped amplifier uses negative feedback.

11) In a swamped amplifier, the effects of the emitter diode become unimportant.

12) The feedback resistor reduces distortion.

13) The feedback resistor stabilizes voltage gain.

14) The ac collector resistance of the first stage includes the input impedance of second stage.

15) If the emitter-bypass capacitor opens, the ac output voltage will decrease.

16) If the emitter-bypass capacitor shorts, the base dc voltage will decrease.

17) If the collector resistor is shorted, the ac output voltage will equal zero.

18) If the load resistance is open, the ac output voltage will increase.

19) In any capacitor is open the ac output voltage will decrease.

20) If the input-coupling capacitor is open, the ac input voltage will equal zero.

21) If the bypass capacitor is open, the ac input voltage at the base will increase.

22) If the output-coupling capacitor is open, the ac input voltage will remain the same.

23) If the emitter resistor is open, the ac input voltage at the base will increase.

24) If the collector resistor is open, the ac input voltage at the base will decrease.

25) If the emitter-bypass capacitor is shorted, the ac input voltage at the base will decrease.

26) If the input impedance of the second stage decreases, the voltage gain of the first stage will decrease.

27) If the BE diode of the second stage opens, the voltage gain of the first stage will increase.

28) If the load resistance of the second stage opens, the voltage gain of the first stage will remain the same.

Chapter 13

1) A JFET is a voltage-controlled device.

2) A uni-polar transistor uses either free electrons or holes but not both.

3) The input impedance of a JFET approaches infinity.

4) The gate controls the width of the channel, drain current and the gate voltage.

5) The gate-source diode of a JFET should be reverse biased.

6) Compared to a bipolar junction transistor, the JFET has a much higher input resistance.

7) The pinchoff voltage has the same magnitude as the gate-source cutoff voltage.

8) When the drain saturation current is less than IDSS, a JFET acts like a resistor.

9) RDS equals pinchoff voltage divided by drain current for zero gate voltage.

10) The transconductance curve is nonlinear.

11) The transconductance increases when the drain current approaches IDSS.

12) A CS amplifier has a voltage gain of gmrd.

13) A source follower has a voltage gain of gmrs/(1 + gmrs)

14) When the input signal is large, a source follower has a voltage gain of less than 1, some distortion and a high input resistance.

15) The input signal used with a JFET analog switch should be small.

16) A cascade amplifier has the advantage of low input capacitance.

17) VHF covers frequencies from 30 to 300 MHz.

18) When a JFET is cut off, the depletion layers are touching.

19) When the gate voltage becomes more negative in an n-channel JFET, the channel between the depletion layers shrinks.

20) If a JFET has IDSS = 8 mA and VP = 4 V, then RDS equals 500 Ω.

21) The easiest way to bias a JFET in the ohmic region is with gate bias.

22) Self-bias produces negative feedback.

23) To get negative gate-source voltage in a self-biased JFET circuit, you must have a source resistor.

24) Transconductance is measured in Mhos or Siemens.

25) Transconductance indicates how effectively the input voltage controls the output current.

Chapter 14

1) A D-MOSFET can operate in the depletion-mode or enhancement-mode.

2) When an n-channel D-MOSFET has ID > IDSS, it is operating in the enhancement mode.

3) The voltage gain of a D-MOSFET amplifier is dependent on RD, RL, and gm.

4) Which of the following devices revolutionized the computer industry? E-MOSFET.

5) The voltage that turns on an EMOS device is the threshold voltage.

6) Which of these may appear on the data sheet of an enhancement-mode MOSFET? VGS(th), ID(on), and VGS(on).

7) The VGS(on) of an n-channel E-MOSFET is greater than VGS(th).

8) An ordinary resistor is an example of a passive load.

9) An E-MOSFET with its gate connected to its drain is an example of an active load.

10) An E-MOSFET that operates at cutoff or in the ohmic region is an example of a switching device.

11) VMOS devices generally switch off faster than BJTs.

12) A D-MOSFET is considered to be a normally on device.

13) CMOS stands for complementary MOS.

14) VGS(on) is always greater than VGS(th).

15) With active-load switching, the upper E-MOSFET is a two-terminal device.

16) CMOS devices use complementary E-MOSFETs.

17) The main advantage of CMOS is its low power consumption.

18) Power FETs are used to switch large currents.

19) When the internal temperature increases in a power FET, the drain current decreases.

20) Most small-signal E-MOSFETs are found in integrated circuits.

21) Most power FETS are used in high-current applications.

22) An n-channel E-MOSFET conducts when it has an n-type inversion layer.

23) With CMOS, the upper MOSFET is complementary.

24) The high output of a CMOS inverter is VDD.

25) The RDS(on) of a power FET has a positive temperature coefficient.