Electronic Devices and Circuit Theory

Robert Boylestad, Louis Nashelsky

Chapter 17 pnpn and Other Devices - all with Video Answers

Educators

Chapter Questions

00:47

Problem 1

Describe in your own words the basic behavior of the SCR using the two-transistor equivalent circuit.

Hunza Gilgit

Numerade Educator

01:20

Problem 2

Describe two techniques for turning an SCR off.

Vishal Gupta

Numerade Educator

01:48

Problem 3

Consult a manufacturer's manual or specification sheet and obtain a turn-off network. If possible, describe the turn-off action of the design.

Amit Srivastava

Numerade Educator

01:35

a. At high levels of gate current, the characteristics of an SCR approach those of what twoterminal device?
b. At a fixed anode-to-cathode voltage less than $V_{(B R) F^{*}}$, what is the effect on the firing of the $\mathrm{SCR}$ as the gate current is reduced from its maximum value to the zero level?
c. At a fixed gate current greater than $I_{G}=0$, what is the effect on the firing of the SCR as the gate voltage is reduced from $V_{(B R) F^{\prime *}}$ ?
d. For increasing levels of $I_{G}$, what is the effect on the holding current?

Chai Santi

Numerade Educator

03:17

Problem 5

a. Based on Fig. 8 , will a gate current of $50 \mathrm{~mA}$ fire the device at room temperature $\left({25}^{\circ} \mathrm{C}\right)$ ?
b. Repeat part (a) for a gate current of $10 \mathrm{~mA}$.
c. Will a gate voltage of $2.6 \mathrm{~V}$ trigger the device at room temperature?
d. Is $V_{G}=6 \mathrm{~V}, I_{G}=800 \mathrm{~mA}$ a good choice for firing conditions? Would $V_{G}=4 \mathrm{~V}$, $I_{G}=1.6 \mathrm{~A}$ be preferred? Explain.

Chai Santi

Numerade Educator

02:19

Problem 6

In Fig. $10 \mathrm{~b}$, why is there very little loss in potential across the SCR during conduction?

Guilherme Barros

Numerade Educator

01:51

Problem 7

Fully explain why reduced values of $R_{1}$ in Fig. 11 will result in an increased angle of conduction.

Hunza Gilgit

Numerade Educator

02:39

Problem 8

Refer to the charging network of Fig. 12 .
a. Determine the dc level of the full-wave rectified signal if a $1: 1$ transformer is employed.
b. If the battery in its uncharged state is sitting at $11 \mathrm{~V}$, what is the anode-to-cathode voltage drop across $\mathrm{SCR}_{1}$ ?
c. What is the maximum possible value of $V_{R}\left(V_{G K} \equiv 0.7 \mathrm{~V}\right)$ ?
d. At the maximum value of part (c), what is the gate potential of $\mathrm{SCR}_{2}$ ?
e, Once $\mathrm{SCR}_{2}$ has entered the short-circuit state, what is the level of $\mathrm{V}_{2}$ ?

Narayan Hari

Numerade Educator

05:36

Problem 9

Refer to the temperature controller of Fig. $13 .$
a. Sketch the waveform of the full-wave rectified waveform across the SCR.
b. What is the peak current through the heater when the SCR is "on" and has a short-circuit equivalent between anode and cathode? Assume each diode has a drop of $0.7 \mathrm{~V}$ when conducting.
c. When the $\mathrm{SCR}$ is on, what is the maximum current through the thermostat?
d. What is the total time for the rise time of the positive pulse of the applied ac voltage from $0 \mathrm{~V}$ to the maximum voltage of the rectified signal?
e. What is the time constant of the capacitor that is charging during the same period of part (d)? How do they compare? Why is this a concern?
f. What is the state of the SCR during this charging period? Why?
g. If the gate-firing potential is $40 \mathrm{~V}$, what is the time period between successive triggering of the SCR?
h. Once the thermostat reaches its set temperature and assumes the short-circuit state, how will the SCR react?
1. What method was used to turn the SCR off: anode current interruption or forced commutation?

Vishal Gupta

Numerade Educator

02:23

Problem 10

Refer to the emergency-lighting system of Fig. $14 .$
a. Sketch the waveform of the full-wave rectified signal across the bulb using a drop of $0.7 \mathrm{~V}$ during conduction of each diode.
b. Determine the peak voltage across the capacitor $C_{1}$ when the $\mathrm{SCR}_{1}$ is off.
c. What is the peak voltage across $R_{1}$ during the charging phase if the battery voltage drops to $5 \mathrm{~V} ?$
d. What is the voltage across the lamp when the SCR turns on and the battery is fully charged at $6 \mathrm{~V}$ ?
e. What is the current drawn from the battery if the lamp is dissipating $2 \mathrm{~W}$ of power?

Jayashree Behera

Numerade Educator

00:37

Problem 11

Fully describe in your own words the behavior of the networks of Fig. 16 .

Hunza Gilgit

Numerade Educator

03:51

Problem 12

What is the suggested turn-off procedure for the network of Fig. 18 ?

Kajal Gautam

Numerade Educator

07:49

Problem 13

For the network of Fig. 19
a. Write an equation for the voltage from gate to ground for the $\mathrm{SCR}$.
b. What is the voltage $V_{G K}$ when $R_{S}=R^{\prime}$ ?
c. Find $R_{S}$ to establish a turn-on voltage of $2 \mathrm{~V}$ if $R^{\prime}=10 \mathrm{k} \Omega$.
d. When the alarm turns on, what is the current through the relay?
e. At $V_{A}=0 \mathrm{~V}$, the maximum de current through the rate-effect resistor will be established. What is its value?
f. When the reset button is activated, is there any reason for concern about spikes in voltage anywhere in the network? How could they be suppressed?

Ryan Kutayiah

Texas A&M University

01:25

Problem 14

a. In Fig. 22, if $V_{Z}=50 \mathrm{~V}$, determine the maximum possible value the capacitor $C_{1}$ can charge to $\left(V_{G K} \cong 0.7 \mathrm{~V}\right)$.
b. Determine the approximate discharge time $(5 \tau)$ for $R_{3}=20 \mathrm{k} \Omega$.
c. Determine the internal resistance of the GTO if the rise time is one-half the decay period determined in part (b).

Prem Bijarniya

Numerade Educator

05:24

Problem 15

a. Using Fig. 24b, determine the minimum irradiance required to fire the device at room temperature $\left(25^{\circ} \mathrm{C}\right)$.
b. What percentage reduction in irradiance is allowable if the junction temperature is increased from $0^{\circ} \mathrm{C}\left(32^{\circ} \mathrm{F}\right)$ to $100^{\circ} \mathrm{C}\left(212^{\circ} \mathrm{F}\right) ?$

Shoukat Ali

Other Schools

01:42

Problem 16

For the network of Fig. 28, if $V_{B R}=6 \mathrm{~V}, \mathrm{~V}=40 \mathrm{~V}, R=10 \mathrm{k} \Omega, C=0.2 \mu \mathrm{F}$, and $V_{G K}$ (fir-
ing potential) $=3 \mathrm{~V}$, determine the time period between energizing the network and the turning on of the SCR.

Kratika Bhadauria

Numerade Educator

03:22

Problem 17

Using whatever reference you require, find an application of a diac and explain the network behavior.

Thao Trinh

Numerade Educator

00:19

Problem 18

If $V_{B R_{2}}$ is $6.4 \mathrm{~V}$, determine the range for $V_{B R_{1}}$ using Eq. (1).

Amy Jiang

Numerade Educator

15:27

Problem 19

Find the level of human body capacitance $C_{b}$ that would result in a 45 -degree phase shift between $v_{i}$ and $v_{G}$ for the network of Fig. $30 .$

Prabhat Tyagi

Numerade Educator

05:01

Problem 20

For the network of Fig. 33, if $C=1 \mu \mathrm{F}$, find the level of $R$ that will result in a $50 \%$ conduction period for the load in either direction if the turn-on voltage for the diac in either direction is $12 \mathrm{~V}$ and the applied sinusoidal signal has a peak value of $170 \mathrm{~V}(=1.414 \times 120 \mathrm{~V})$ at $60 \mathrm{~Hz}$

Nikhil Tiwari

Numerade Educator

03:13

Problem 21

For the network of Fig. 40, in which $V=40 \mathrm{~V}, \eta=0.6, V_{V}=1 \mathrm{~V}, I_{V}=8 \mathrm{~mA}$, and $I_{P}=10 \mu \mathrm{A}$, determine the range of $R_{1}$ for the triggering network.

Narayan Hari

Numerade Educator

03:35

Problem 22

For a unijunction transistor with $V_{B B}=20 \mathrm{~V}, \eta=0.65, R_{B_{1}}=2 \mathrm{k} \Omega\left(I_{E}=0\right)$, and $V_{D}=0.7 \mathrm{~V}$, determine:
a. $R_{B_{2}}$.
b. $R_{B B}$.
c. $V_{R_{\tilde{\mathrm{B}}}}$
d. $V_{P}$.

Amit Srivastava

Numerade Educator

01:35

Problem 23

Given the relaxation oscillator of Fig. 68 :
a. Find $R_{B_{1}}$ and $R_{B_{2}}$ at $I_{E}=0 \mathrm{~A}$.
b. Determine $V_{P}$, the voltage necessary to turn on the UJT.
c. Determine whether $R_{1}$ is within the permissible range of values defined by Eq. (8).
d. Determine the frequency of oscillation if $R_{B_{1}}=200 \Omega$ during the discharge phase.
e. Sketch the waveform of $v_{C}$ for two full cycles.
f. Sketch the waveform of $v_{R_{2}}$ for two full cycles.
g. Determine the frequency using Eq. (17) and compare to the value determined in part (d). Account for any major differences.

Varsha Aggarwal

Numerade Educator

03:41

Problem 24

For a phototransistor having the characteristics of Fig. 50 , determine the photoinduced base current for a radiant flux density of $5 \mathrm{~mW} / \mathrm{cm}^{2}$. If $h_{f e}=40$, find $I_{\mathrm{C}}$.

Mohamed Raafat Mohamed

Numerade Educator

00:58

Problem 25

Design a high-isolation OR-gate employing phototransistors and LEDs.

Chai Santi

Numerade Educator

02:22

Problem 26

a. Determine an average derating factor from the curve of Fig. 58 for the region defined by temperatures between $-25^{\circ} \mathrm{C}$ and $+50^{\circ} \mathrm{C}$.
b. Is it fair to say that for temperatures greater than room temperature (up to $100^{\circ} \mathrm{C}$ ), the output current is somewhat unaffected by temperature?

Vishal Gupta

Numerade Educator

01:48

Problem 27

a. Determine from Fig. 54 the average change in $I_{C E O}$ per degree change in temperature for the range $25^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$.
b. Can the results of part (a) be used to determine the level of $I_{C E O}$ at $35^{\circ} \mathrm{C}$ ? Test your theory.

Clarissa Noh

Numerade Educator

01:53

Problem 28

Determine from Fig. 55 the ratio of LED output current to detector input current for an output current of $20 \mathrm{~mA}$. Would you consider the device to be relatively efficient in its purpose?

Vinnu M

Numerade Educator

02:53

Problem 29

a. Sketch the maximum-power curve of $P_{D}=200 \mathrm{~mW}$ on the graph of Fig. $56 .$ List any noteworthy conclusions.
b. Determine $\beta_{\mathrm{dc}}$ (defined by $I_{C} / I_{F}$ ) for the system at $V_{C E}=15 \mathrm{~V}, I_{F}=10 \mathrm{~mA}$.
c. Compare the results of part (b) with those obtained from Fig. 55 at $I_{F}=10 \mathrm{~mA}$. Do they compare? Should they? Why?

Mirza Aslam Beig

Numerade Educator

12:58

Problem 30

a. Referring to Fig. 57 , determine the collector current above which the switching time does not change appreciably for $R_{L}=1 \mathrm{k} \Omega$ and $R_{L}=100 \Omega$.
b. At $I_{C}=6 \mathrm{~mA}$, how does the ratio of switching times for $R_{L}=1 \mathrm{k} \Omega$ and $R_{L}=100 \Omega$ compare to the ratio of resistance levels?

Jayashree Behera

Numerade Educator

01:21

Problem 31

Determine $\eta$ and $V_{G}$ for a PUT with $V_{B B}=20 \mathrm{~V}$ and $R_{B_{1}}=3 R_{B_{2}}$

Lucas Finney

Numerade Educator

04:38

Problem 32

Using the data provided in Example 3 , determine the impedance of the PUT at the firing and valley points. Are the approximate open- and short-circuit states verified?

Narayan Hari

Numerade Educator

05:54

Problem 33

Can Eq. (24) be derived exactly as shown from Eq. (23)? If not, what element is missing in Eq. $(24) ?$

Jose Martinez

Numerade Educator

03:13

Problem 34

a. Will the network of Example 3 oscillate if $V_{B B}$ is changed to $10 \mathrm{~V}$ ? What minimum value of $V_{B B}$ is required ( $V_{V}$ a constant)?
b. Referring to the same example, what value of $R$ would place the network in the stable "on" state and remove the oscillatory response of the system?
c. What value of $R$ would make the network a 2 -ms time-delay network? That is, would provide a pulse $v_{K}$ at $2 \mathrm{~ms}$ after the supply is tumed on and then stay in the "on" state.

Narayan Hari

Numerade Educator

Problem 1

Problem 2

Problem 3

Problem 4

Problem 5

Problem 6

Problem 7

Problem 8

Problem 9

Problem 10

Problem 11

Problem 12

Problem 13

Problem 14

Problem 15

Problem 16

Problem 17

Problem 18

Problem 19

Problem 20

Problem 21

Problem 22

Problem 23

Problem 24

Problem 25

Problem 26

Problem 27

Problem 28

Problem 29

Problem 30

Problem 31

Problem 32

Problem 33

Problem 34