chapter 1 voltage regulator [compatibility mode]
DESCRIPTION
Chapter 1 VOLTAGE REGULATORTRANSCRIPT
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SEE 3263SEE 3263
ELECTRONIC SYSTEMSELECTRONIC SYSTEMS
1
DR. RUBITA [email protected]: 07- 5535270
C 1:C 1:
SEE 3263: ELECTRONIC SYSTEMS
2
1.0
.
.
.
A .
E 240, 50H
.
A , .
A
.
F ( )
.
.
A .
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DC POWER SUPPLY BLOCK DIAGRAM
5
/
6
These power supplies were constructed using
discrete components, integrated circuits or
combination of both.
7
Discrete power transistor, op-amp and
comparator were used to complete the circuit.
POWER SUPPLY REGULATION
An ideal power supply provides a
constant dc voltage despite changes tothe input voltage or load conditions.
8
The output voltage of a real powersupply changes under load and is alsosensitive to input voltage changes.
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VOLTAGE REGULATION
2 basic categories:
(i) Load Regulation - Output voltagenearly constant when load change.
9
(ii) Line Regulation - Output voltagenearly constant when line voltage
change.
Load regulationLoad regulationis a measure of how well apower supply is able to maintain the dc output
voltage between no load and full load with the
input voltage constant.
LOAD REGULATION
10
,
when load current increases.
VO(NL) output voltage with no
load.
VO(FL) output voltage with fullload.
IL(FL) full load current (maximum
current that coming out
from power supply).
Load regulation can be expressed as a
percentage change in load voltage.
Load Regulation = %100V
VV
)FL(O
)FL(O)NL(O
Load re ulation can also be ex ressed in terms
11
of percent change in the output per mA changein load current (%/mA).
%100II
V
VV
%100I
V
V
VL(NL)L(FL)
O(FL)
O(FL)O(NL)
L
O
O
reg
=
=
EXAMPLE:
A regulated power supply with an output resistance of 1 deliver a full load current of 1A to a 25 load. What is the
load regulation?
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V25)25)(A1(RIV L)FL(L)FL(O ===
13
)NL(O)NL(O
OL
L)FL(O V
125
25V
RR
RV
+=
+=
V26V)NL(O =
%4%10025
2526%100
V
VVV%
)FL(O
)FL(O)NL(O
reg =
=
=
.
LINE REGULATION
14
() ,
.
Line regulation can be expressed as:
LINE REGULATION
%100V
V
i
O
Line Regulation =
15
%100V
VV
i
O
O
Line regulation can also be expressed in termsof percent change in VO per volt change on the
Vi (%/V).
Line Regulation =
5, 0.25.
15. D
%/.
:
F ,
(0%).
V/%333.0%100V5
V15.
=Line Regulation =
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ZENER REGULATOR
17
>
&
,
,
EALE:D:
() I() I() .
() D() D() .() , , .
mA45.512
mA60R
VIIII
(min)L
OS(max)LS(min)Z ====
220
mA4012
mA60V
IIII OS(min)LS(max)Z ====
mA60100
1218IS =
=
=
S
Oi
R
VV
(max)L
mW480)12)(mA40(VIP Z(max)Z(max)DZ ===
mW36.0100)mA60(R)I(P 2S2
SRS ===
19
mW4.65)12)(mA45.5(VIP Z(min)Z(min)DZ ===
() .
()
.2 .
20
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EECIE:F ,
.
G: = 5.1 I= 35 A
IK= 1 A, = 12 , I= 70 A
21
.
III LE ==
)1()1( ++
)1(
II-III LSBSZ
+==
BEZO -VVV =
EXAMPLE 1.4 (pg 1-14):If = 50, determine:(a) output voltage, VO (b) voltage, VCE1(c) current, IS (d) current, IZ
(b) Vi = VCE + VOVCE = Vi VO = 20 11.35 = 8.65 V
23
i = S S Z
IS = = = 0.04 A
(d)
= 39.78 mA
S
Zi
R
VV
200
1220
A55.222mA40III
A55.222
51
mA35.11
1
I
1
II
mA35.11k1
V35.11
R
VI
BSZ
LEB
L
OL
==
==
+
=
+
=
===
(a) VO = VZ VBE =12 0.65 = 11.35 V
DP
L
DP
1E2B III
=
=
A Darlington pair transistor (a very high DC) can beused to increase the current gain. This will reducethe base current and the zener power rating will below.
24
BEZO
DP
LS
2BSZ
2121DP
V2VV
II
III
=
=
=
++=
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Design a Darlington series-pass voltage regulatorlike that of figure shown below from the followingrequirements: VDC(in) = 18V, VDC(out) = VE = 12V, IL(max) =2A.
25
EGLA CICI IH FEEDBACKEGLA CICI IH FEEDBACKQ1
Q2
R4
R1
RL
IL
I4
IB1
IC2 - VZ +VIN +VO
VRR
RV
VRR
RV
VVV
2
21
2O
O
21
22
Z2BE2
+=
+=
+=
R3R2
B2 +VBE2
-
+V2-
VB1 = VCE2 -
26
)VV(R
R1V Z2BE
2
1O +
+=
Any change in VO must cause a change in VBE1 to maintainthe equality. If VO decreases, VBE1 must increase since VZis constant. Similarly if VO increases, VBE1 must decrease.
ILE EIE LAGE EGLAILE EIE LAGE EGLA
BLCK DIAGABLCK DIAGA
CONTROL
ELEMENTVIN VOUT
REFERENCE
VOLTAGE
ERROR
DETECTOR
SAMPLE
CIRCUIT
27
Series Regulators
Series Regulator block diagram:
Basic series re ulator circuit:
VIN VOUT
Error
detector
Sample
circuit
Control
element
Reference
voltage
28
VIN VOUT
R1
Control element
Q1
D1
VREF+
Error detector
R2
R3
Sample
circuit
The control elementmaintains a constant outputvoltage by varying the
collector-emitter voltageacross the transistor.
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BAIC BAIC A EIE EGLAA EIE EGLA
+
Q1
R2R1
RL
IL
V+ =VZ
VIN+
-R3
+
VZ-
V- O
-
29
Z
3
2O V
RR1V
+=
VR
R1V Z
2O
+=
EALE:F :
() ?
() I 200A, 1?
( )
W16.1
)A2.0(V2.12V18VIP
=
==
30
V2.12
V9.3k47
k1001
=
+=
ECI CICIECI CICI
2 :
1. /
2.
LIEA CE LIIIG CICILIEA CE LIIIG CICI
32
I
L() . I
L> I
L(),
IL IL(). IL
L .
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33
. 2
0. 2 .
1,
..SC
(max)LR
V7.0I =
The currentlimit is:
EXAMPLE:
34
A A
25 . , 25 . , CC , I , IL()L() 0.5 A? 0.5 A?
CC, , LL= 100= 100 LL= 10= 10??
FLDBACK CE LIIIGFLDBACK CE LIIIG
CICICICI
35
D = 0 IL= IC,
D=()IC= (20 0)1A= 20 ( )
D
=(
)IC
= (20 0)0.5A=10 ( )
D = 15 IL= 1 A,
36
D= ()IL= (20 15)1 A = 5 ( )
D ,
20 1
. 10 .
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EIE EGLA IH FLDBACKEIE EGLA IH FLDBACK
CE LIIIGCE LIIIG
37
FoldFold--back current limitingback current limitingdrops the load current wellbelow the peak during overload conditions. Q2 conductswhen VR4 + VBE2 = VRSC and begins current limiting.
VBE2 = VRSC VR4
VR4 will increase or decrease if VO increases ordecreases. At this instant, Q2 is still not conducting. VR4 isfound by applying the voltage-divider rule:
( )ORSC54
44R VV
RR
RV +
+=
38
When IL increase to IL(max) or during overload, VR4 will dropbecause VO drops. A smaller value of VRSC is required tomaintain VBE2 0.7V. This means that less current isneeded to maintain conduction in Q2 and the load current
drops.
At this point, current limiting occurs. IL will be limited and Q2conducting (ON).
39
If the regulated output voltage is 10 V, determine:
(a) The short circuit current, ISC(b) The maximum load current, IL(max)(c) Power dissipation in transistor 2N3055 during shorted load.
Q1Vi =23V
R11.2
RSC
Test Question Example:For the circuit shown below, determine :(a) Maximum load current.(b) Output voltage range.(c) Values of VB1 and IR2 if RL = 10 and VO = 15 V.
40
Q2
Q3
VZ =10V
R23k
R33.3k
R45k
R510k
RL
IR2
B1
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Final Exam Question Example:
41
A series voltage regulator circuit above produce an output voltage, VO =10 V and a maximum load current, IL(max) = 1 A. Given for all transistors,Q1, Q2, and Q3 : = hFE = 100, VBE(ON) = 0.7 V; for Zener diode, DZ : VZ =4.3 V, rZ = 0 , IZK = 1 mA and IZM = 40 mA. The unregulated inputvoltage, Vi is 20 V. During optimum operation, I1=2 mA, IZ = 14 mA, I3 =1 mA and IB3 can be neglected.
Final Exam Question Example:
42
Draw a basic block diagram for this regulator circuit.Sketch an label clearly the graph of VO versus IO.
Briefly explain how the output voltage, VO is maintain constant evenwhen the input voltage, Vi varies within the permitted range.
Final Exam Question Example:
43
Explain the function of resistors, R1 and R2.
Determine the resistor value of R1 and R2.
Determine the resistor value of R3 and R4.
Determine the suitable range value of RL.
Final Exam Question Example:
44
Determine the power dissipation in Q1, Q2 and DZ at Optimumoperation.
The pass transistor Q1 will easily burnt when load RL is shorted.Suggest one circuit that can be used to overcome the problem.Briefly explain how this additional circuit works.
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SHUNT-TYPE VOLTAGEREGULATOR BLOCK DIAGRAM
45
Shunt Regulators
Shunt Regulator block diagram:
VIN
R1
VOUT
ControlErrorReference
46
Basic shunt regulator circuit:e ement(shunt)
Samplecircuit
detectorvoltage
VIN
VOUT
R2
Q1
+
D1
R4
R3 RL
VREF
Error detectorControl
element
Sample
circuit
R1
The control elementmaintains a constant outputvoltage by varying thecollector currentin thetransistor.
H LAGE EGLAH LAGE EGLA
IH IH AA
Shunt regulators use a
parallel transistor for the
control element. If the output
47
Although it is less efficient than the series regulator, the
shunt regulator has inherent short-circuit protection. The
maximum current when the output is shorted is VIN
/R4.
voltage changes, the op-amp
senses the change and
corrects the bias on Q1. A
decrease in output voltage
causes a decrease in VB
and
an increase in VC.
SWITCHING REGULATORS
To reduce power dissipation in pass transistor.
Gives higher efficiency.
Able to supply very large load current with lowvoltage as required in the PC.
48
step-down
step-up
inverting
Step-down switching regulator is widely used as
the power supply in PC.
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Switching Regulators
All switching regulators control the output voltage byrapidly switching the input voltage on and off with a dutycycle that depends on the load. Because they use highfrequency switching, they tend to be electrically noisy.
49
VC
ton toff ton toff ton toff tonon/offcontrol
VOUT
Switching Regulators
All switching regulators control the output voltage byrapidly switching the input voltage on and off with a dutycycle that depends on the load. Because they use highfrequency switching, they tend to be electrically noisy.
50
ton toff ton toff ton toff ton
VC
on/offcontrol
VOUT
An increase in the duty cycle increases the output voltage.
Switching Regulators
All switching regulators control the output voltage byrapidly switching the input voltage on and off with a duty
cycle that depends on the load. Because they use highfrequency switching, they tend to be electrically noisy.
51
VC
ton toff ton toff ton toff tonon/offcontrol
VOUT
A decrease in the duty cycle decreases the output voltage.
BASIC SWITCHING REGULATOR
R1+
Vi
Q 1
Gated
Latch
R 3
I L
C
L
D1PWM
52
L o
-
+
-
V2+
-Pengayun
+
-V
Z
R2
Vralat
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57
=
=
T
TVV
T
TCycleDuty
HIHIdc
HI
EXAMPLEBy assuming an ideal LC,By assuming an ideal LC,(a)(a) Explain the function of PWM, DExplain the function of PWM, D11, L and C., L and C.(b)(b) Explain the operation of the circuit if VExplain the operation of the circuit if VOUTOUT decreases.decreases.
(c)(c) Calculate VCalculate VOUTOUT..(d)(d) If VIf Vii increase to15 V, sketch the waveform at point Bincrease to15 V, sketch the waveform at point B
in order to maintain the value found inin order to maintain the value found in (c).(c).
58
59
PWM is used to produce pulse trains with pulse width depend on thePWM is used to produce pulse trains with pulse width depend on thechanges in output, Vchanges in output, VOUTOUT. These pulse trains (at point B) will control the ON. These pulse trains (at point B) will control the ONand OFF interval of Qand OFF interval of Q11 thus will finally increase or decrease the value ofthus will finally increase or decrease the value ofVVOUTOUT..
The diode DThe diode D11 is used to eliminate the negative voltage.is used to eliminate the negative voltage.
Inductor, L and capacitor, C is used as filter to average the switchedInductor, L and capacitor, C is used as filter to average the switchedvoltage thus producevoltage thus produce VVDCDC..
60
When VOUT reduced, VR2 will also reduced thus Verror will increase becauseVZ is constant.PWM will produce pulse trains with large pulse width.Q1 will ON and OFF with large duty cycle thus increase the dc currentflowing through it.
The increase of dc current in Q1 will then increase the VOUT that try toreduce previously.This regulating action maintains VOUT at an essentially constant level.
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61
V5.712m6m10
m10V
TT
TV i
OFFON
ONOUT =
+=
+=
msT
m
T.
V
T
TV
ON
ON
iON
OUT
8
1516
57
=
=
=
8 ms
8 ms
ICHIG EGLA IHICHIG EGLA IH
CCI CCI
CC , , EEAD AD
LAGELAGE
VERROR
VOSC
VAT
VH
V1
+
(V )
-
(V )
TON
VOSC
VH
V1
-
(V )
VERROR
+
(V )
VDC
TON
+T
OFF
TON
TON
+T
OFF(a)
(b)
0
0 t
t
PWM GENERATION USING SAWTOOTHGENERATOR AND VOLTAGE COMPARATOR
64
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:
Higher efficiency.Higher efficiency.
Light and compact.Light and compact.
Filtering is easy to achieve at high frequencies.Filtering is easy to achieve at high frequencies.
VVOO VVii
65
Generate EMI (Generate EMI (electromagnetic interferenceelectromagnetic interference) where switching at high) where switching at high
frequency for Qfrequency for Q11 current will produce large magnetic fields whichcurrent will produce large magnetic fields which
induced noise voltage around conductor.induced noise voltage around conductor.
Limited performance of power transistor (pass transistor) to switchLimited performance of power transistor (pass transistor) to switch
ONONandand OFFOFFat high speed.at high speed.
Contain large noise and ripple in VContain large noise and ripple in VOO..
Vi
Series
Element
Protection
Circuit Vo
66
Comparator
Amplifier
Reference
VoltageSampling
Circuit
IC voltage regulators are available asseries regulators or as
switching regulators. The popular three-terminal regulators areoften used on separate pc boards within a system because theyare inexpensive and avoid problems associated with large powerdistribution systems (such as noise pickup).
IC EGLA 78 EIEIC EGLA 78 EIEThe only external components required with the 78XX seriesare input and output capacitors and some form of heat sink.
These IC include thermal shutdown protection and internal
current limiting.
The 78XX series is a fixed positive outputregulator available in various packagesand with standard voltage outputs.
They are primarily used for fixed outputvoltages, but with additional components,they can be set up for variable voltages orcurrents.
DD--PAKPAK TOTO--220220
TOTO--33
IC EGLA 78 EIEIC EGLA 78 EIE
11 33
22
- Can produce output current in excess of 1A
- VIN must be at least 2V- 3V above the output voltage
- C1 to prevent from unwanted oscillation
- C2 act as a line filter to improve transient response
Type number Output voltage
7805
7806
7808
7809
78127815
7818
7824
+5.0 V
+6.0 V
+8.0 V
+9.0 V
+12.0 V+15.0 V
+18.0 V
+24.0 V
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IC EGLA 79 EIEIC EGLA 79 EIE
22 33
11
The 79XX series is the negativeoutput counterpart to the 78XX
series, however the pin assignmentsare different on this series.
Other specifications are basicallythe same.
7905
7905.2
79067908
7912
7915
7918
7924
5.0 V
5.2 V
6.0 V8.0 V
12.0 V
15.0 V
18.0 V
24.0 V
Type number Output voltage
LIEA IC EGLA L317LIEA IC EGLA L317
R1
+VOUT+VIN LM317
IREFVREF1
23
+ve output regulator
The LM317 is an adjustable positive output IC regulator.There is a fixed reference voltage of +1.25 V between theoutput and adjustment terminals. There is no ground pin.
R2IREF+ IADJ
IADJ
70
2ADJ
1
2REFOUT RI
R
R1vV +
+=
VREF = 1.25V
Maximum Current 1.5A
Output may varies 1.2V 37V
Input voltage 4V 40 V
The output voltage is calculated by:The output voltage is calculated by:
The LM337 is an adjustable negative output IC regulator.
Example:What is the value of VOUT? (Assume IADJ is 50 A):
V
kAk
VVOUT
02.18
)2)(50(
150
2125.1
=
+
+=
71
IC EGLA IH BE CEIC EGLA IH BE CE
VINQext
IC regulators are limited to a maximum allowable currentbefore shutting down. The circuit shown is uses anexternal pass transistor to increase the maximumavailable load current.
Rext sets the
RL
VOUT78XX
RextC1
C2
72
point whereQext begins toconduct:
max
extI
V7.0R =
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IC EGLA IH EEALIC EGLA IH EEAL
CE LIIIG CICICE LIIIG CICI
VOUT
VIN
78XX
Qext
Rext
Rlim
Qlim
RL
73
Previous slide shows that the external transistor is not
protected from excessive current, such as would resultfrom a shorted output. An additional current-limitingcircuit (Qlim and Rlim) can be added to protect Qext fromexcessive current and possible burn out.
EALEEALE
An IC voltage regulator shown below is able to operatewith a much higher output current, IL. If given VEB1(ON) =V
EB2(ON)= 0.7 V, I
O(max)= 1A and
1= 15:
(a) Explain the function of transistors Q1 and Q2.(b) Determine IC1 and IO when RL = 100 and 1 .
(a) Explain the function of transistors Q1 and Q2.
Q1 act as an external pass transistor to handle excesscurrent that is unable to be handled by three-terminalIC regulator.
Q2 act as the current limiting circuit to protect Q1 fromexcessive maximum current.
(b) Determine I and I when R = 100 and 1 .
IR1
IB1
When VEB1
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When RL = 100 and 1 , the values of IC1 and IO can
be found as tabulated in the table below.
L L B1 C1 O
100 50 mA 0A 0A 50 mA
1 5000 mA 297.92 mA 4468.8 mA 531.2 mA
77
A CE EGLAA CE EGLA
V
IC regulators can be used as a current source when anapplication requires that a constant current can be
supplied to a variable load. R1 is the current-settingresistor.
R1
RL
IOUT
ILIG
VOUTGND PIN
78
G
1
OUTL IR
VI +=
E L IH E L IH
EIAL LAGEEIAL LAGE
7815In Out
GndC1
10 uF20V
4000 uF30V
240V
50 Hz
C2
VO1
24V
24V
79
7915In Out
GndC
3 C
4
10 uF
20V
4000 uF
30V
N1
N2
:
VO2
IC Voltage Regulators
The 78S40 is an IC containing all of the elements neededto configure a switching regulator, using a few externalparts.
It is a universal switchinguniversal switchingre ulator subs stemre ulator subs stem
VINCT
CS
VCC
Noninvert
input
Invert
input Gnd
Timing
capVCC
Ipksense
Driver
collector
Switch
collector
80
because it can be configuredas a step-down, step-up, orinverting regulator by theuser. The data sheet showstypical circuits for theseconfigurations.
+
10 11 12 13 14 15 16
7 6 5 4 3 2 1
+
Q1
Q2
SOscillator
R
Q
Comp.
Flip-flop
VOUT
R1
L
CO
R2
1.25 Vreference
D1
8
9
+
9 10 11 12 13 14 15 16
8 7 6 5 4 3 2 1
Referencevoltage
Invertinput
Noninvertinput
VCCop-amp
Output Switchemitter
Anode Cathode
+
Q1
Q2
SOscillator
R
Q
Comp.
Flip-flop
1.25 Vreference
D1
Here is the step-downconfiguration.
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81 82
EIE LAGE EGLA IH CAEIE LAGE EGLA IH CA
CE LIIIG IG L 723CE LIIIG IG L 723
723
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Regulator
Line regulation
A
.
() .
SummarySummarySummary
Load regulation
Linear regulator
Switchingregulator
.
A
.
A
.
DEADIG EIDEADIG EI
The load regulation of an ideal power supply is
________.
(a) 0%(a) 0%
(b) 25%
(c) 50
(d) 100%
(e) none of the above
DEADIG EIDEADIG EI
An AC-DC converter power supply contains all of thefollowing except a ________.
(a) rectifier circuit
(b) filter circuit
(c) sample-and-hold circuit
(d) regulator circuit
(e) none of the above
(c) sample-and-hold circuit
DEADIG EIDEADIG EI
The ideal voltage regulator maintains a constant DCoutput voltage regardless of changes in __________.
(a) its input voltage
(b) its output voltage demand
(c) its load current demand
(d) both (a) and (c)
(e) none of the above
(d) both (a) and (c)
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DEADIG EIDEADIG EI
Under full load condition, ___________.
(a) the input voltage is at its maximum value
(b) the load resistance is at a minimum value
(c) no load resistance is present
(d) the load current is at a minimum value
(e) none of the above
(b) the load resistance is at a minimum value
DEADIG EIDEADIG EI
__________ is a measurement of how well thepower supply maintains a constant voltage across
the load with changes in load current.
(a) Voltage control
(b) Load voltage control
(c) Load regulation
(d) Line regulation
(e) none of the above
(c) Load regulation
DEADIG EIDEADIG EI
What is the load regulation of a power supply with ano load voltage of 16.5 V and a full load voltage of15 V?
(a) 1.5%
(b) 9.1%
(c) 10%
(d) 90.9%
(e) none of the above
(c) 10%
DEADIG EIDEADIG EI
__________ is a measurement of how well thepower supply maintains a constant output voltagewith changes in input voltage.
(a) Voltage control
(b) Load voltage control
(c) Load regulation
(d) Line regulation
(e) none of the above
(d) Line regulation
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DEADIG EIDEADIG EI
The pass transistor in linear regulators will_________.
(a) operate in the linear area at all times(a) operate in the linear area at all times
(b) be in cutoff at all times
(c) be in saturation at all times
(d) switch between cutoff and saturation
(e) none of the above
DEADIG EIDEADIG EI
Switching regulators have _________ than linearregulators.
(a) longer life
(b) simpler circuitry
(c) a higher cost in all cases
(d) greater efficiency
(e) none of the above
(d) greater efficiency
A correct formula for load regulation is _________.
OUT
INLoad Regulation = 100%
V
V
a.
95
( )OUT OUT
IN
/ 100%Load Regulation = V VV
d.
FL
NL FL
Load Regulation = 100%V
V V
c.
NL FL
FL
Load Regulation = 100%V V
V
b.
(a) output resistance and the full-load
An alternate way to express load regulation is interms of the _________.
(a) output resistance and the full-load
res s ance
(b) output resistance and the shorted-loadresistance
(c) input resistance and the full-load resistance
(d) input resistance and the shorted-loadresistance
res s ance
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a 0.5 A VIN VOUTQ1 R4
In the circuit shown, R4 = 0.7 . The output currentwill be limited to _________.
(b) 0.7 A
(c) 1.0 A
(d) 1.4 A
R1
R3
R2
Q2
Current limiter
+
0.7
(c) 1.0 A
97
(a) control element
The block diagram for a series voltage regulator isshown. The yellow box represents a _________.
(b) sample circuit
(c) error detector
(d) reference voltage
IN OUT
?
98
(d) reference voltage
(a) control element VIN
R1
VOUT
The block diagram for a shunt voltage regulator isshown. The yellow box represents a _________.
(b) sample circuit
(c) error detector
(d) reference voltage
?
99
(b) sample circuit
(a) high speed switching circuit(b) fold-back current limiter
The circuit in the blue shaded area is a _________.
(b) fold-back current limiter
(c) reference source
(d) shunt regulator+VIN VOUT
R1
Q1
+
Q2
R4
D1
R3
R2
R6
R5
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a low noise
A major advantage of all switching regulators is
_________.
(b) high output impedance
(c) high efficiency
(d) all of the above
101
(c) high efficiency
(a) series linear
+VIN
VOUTQ1 D1
on
offC+VIN
VOUTQ1 D1
on
off+VIN
VOUTQ1 D1
The type of regulator circuit shown is a _________.
(b) series switching
(c) shunt switching
(d) none of the above
R1
R3
R2 RL
D2
Variable
pulse-width
oscillator
L
+
C+
L fieldbuilds
esR1
R3
R2 RL
D2
Variable
pulse-width
oscillator
L
+
C
L fieldcollapses
+Ccharges
R1
R3
R2 RL
D2
Variable
pulse-width
oscillator
L
+
C
102
(d) none of the above
(a) +5 V
The output voltage from a 7912 is a regulated_________.
(b) +12 V
(c) 5 V
(d) 12 V
103
() 12 V
104