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1
ElectronicsElectronics
Principles & ApplicationsPrinciples & ApplicationsSixth EditionSixth Edition
Chapter 4Power Supplies
©2003 Glencoe/McGraw-Hill
Charles A. Schuler
2
• The System• Half-Wave Rectification• Full-Wave Rectification• RMS to Average• Filters• Multipliers• Ripple and Regulation• Zener Regulator
INTRODUCTION
3
Power Supply
Circuit A
Circuit B
Circuit C
The power supply energizes the other circuits in a system.
Thus, a power supply defect will affect the other circuits.
4
ac Power Supply
Circuit A
Circuit B
Circuit C
dc
dc
dc
Most line operated supplies change ac to dc.
5
+
-
0
+
-
0ac
Half-wave pulsating dc
The cathode makes thisthe positive end of the load.
A series rectifier diode changes ac to dc.
6
+
-
0
Full-wave pulsating dc
+
-
0
ac
The cathodes make thisthe positive end of the load.
Two diodes and a transformer provide full-wave rectification.
7
VLOAD is equalto one-half thetotal secondary
voltage.
C.T.
½ VTOTAL
VTOTAL
Only half of the transformer secondary conducts at a time.
8
+
-
0
Full-wavepulsating dc
+
-
0
ac
The bridge circuit eliminates the need for a transformer.
9
+
-
0 Full-wavepulsating dc
+
-
0
ac
Reversing the diodes produces a negative power supply.
10
Power Supply Basics QuizMost line-operated power supplies change ac to ________. dc
A single diode achieves ________ -wave rectification. half
Two diodes and a center-tapped transformerprovide ________ -wave rectification. full
A bridge rectifier uses ________ diodes. four
The positive end of the load is the end in contact with the diode ________. cathodes
11
Vac
Vdc
ac
Vac
Vdc
Ignoring diode loss,the average dc is 45%
of the ac input forhalf-wave.
Vac
Vdc
Converting rmsto average
12
Vac
Vdc
ac
Vac
Vdc
Ignoring diode loss,the average dc is 90%
of the ac input forfull-wave.
13
0 V
-200 V
+200 V
20 ms 40 ms0 ms
3 120 V60 Hz
Three-phase rectification is used in commercial,industrial and vehicular applications.
Full-wave, 3 bridge
Vdc = 1.35 x Vrms = 162 V
14
10 20 30 400
Time in milliseconds
40
80
120
160
200
0
Vol
tsThree-phase rectifier output
Vdc = 1.35 x Vrms = 162 V
15
Average dc QuizThe average dc voltage with half-wave isequal to ______ of the ac voltage. 45%
The effective ac voltage in a two-diode, full-wave rectifier is _______ of the secondary voltage.
half
The average dc voltage with a full-waverectifier is _________ of the effective ac voltage.
90%
The average dc voltage with a bridge rectifieris equal to ________ of the ac voltage. 90%
The average dc voltage with a 3 bridge rectifier is equal to ________ of the ac voltage. 135%
16
Filtercapacitor
+
-
0
Charge
Discharge
VP
A relatively large filter capacitor will maintain theload voltage near the peak value of the waveform.
ac
17
ac
+
-
0
Discharge time is less.
Full-wave is easier to filter since the discharge time is shorter than it is for half-wave rectifiers.
VP
18
Adding a filter capacitorincreases the dc output
voltage.
Vac
Vdc
ac
Vac
Vdc
Ignoring diode lossand assuming a largefilter, the dc output is
equal to the peak valuefor both half-wave and
full-wave.
19
Vac
Vdc
Vac
Vdc
ac
Ignoring diode lossand assuming a largefilter, the dc output is
equal to the peak valuefor both half-wave and
full-wave.
20
ac
Vac
Vdc
Full-wave doublerVac
Vdc
Ignoring diode loss andassuming large filters,
the dc output is twice thepeak ac input.
21
C1 is charged.
C1ac
Half-wave voltage doubler
C2
The charge on C1 adds to the ac line voltageand C2 is charged to twice the peak line value.
22
Capacitive Filter dc Output Quiz(Ignore diode loss and assume a light load for this quiz.)
The dc output in a well-filtered half-wave supply is _____ of the ac input. 141%
The dc output in a well-filtered full-wave supply is _____ of the ac input. 141%
The dc output in a well-filtered half-wave doubler is _____ of the ac input. 282%
The dc output in a well-filtered full-wave doubler is _____ of the ac input. 282%
23
Vac
Vdc
Vac
Vdc
An ideal dc power supply has no ac ripple.
ac ripple = 0%
24
Vac
Vdc
Vac
Vdc
acac ripple =
12 Vdc
1.32 Vac x 100% = 11 %
Real power supplieshave some ac ripple.
25
Vac
Vdc
An ideal power supply has perfect voltage regulation.
The voltagedoes not change.
26
Vac
Vdc
Vac
Vdc
ac
The output of areal supply drops
under load.
Voltage Regulation =VVFL
x 100 %
= 12 V1 V
x 100 %
= 8.33 %
27
0246
5
10
15
20
25
30
35
Reverse Bias in Volts
ReverseCurrentin mAI
V
Vrev
The voltage across a conductingzener is relatively constant.
81012
28
ac
Vac
Vdc
A shunt zener diode canbe used to regulate voltage.
Vac
Vdc
Vac
Vdc
If the zener stops conducting, the regulation is lost.
29
Power Supply Quality QuizThe voltage regulation of an ideal powersupply is ___________. 0%
The ac ripple output of an ideal powersupply is ___________. 0%
small
The ac component of an ideal dc power supply should be as ________ as is feasible. small
A device that is commonly used to regulatevoltage is the ________ diode. zener
V in a real power supply should be as ___________ as is feasible.
30
REVIEW
• The System• Half-Wave Rectification• Full-Wave Rectification• RMS to Average• Filters• Multipliers• Ripple and Regulation• Zener Regulator
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
ElectronicsElectronics
Principles & ApplicationsPrinciples & ApplicationsSixth EditionSixth Edition
Chapter 4Power Supplies
©2003 Glencoe/McGraw-Hill
Charles A. Schuler
54
• The System• Half-Wave Rectification• Full-Wave Rectification• RMS to Average• Filters• Multipliers• Ripple and Regulation• Zener Regulator
INTRODUCTION
55
Power Supply
Circuit A
Circuit B
Circuit C
The power supply energizes the other circuits in a system.
Thus, a power supply defect will affect the other circuits.
56
ac Power Supply
Circuit A
Circuit B
Circuit C
dc
dc
dc
Most line operated supplies change ac to dc.
57
+
-
0
+
-
0ac
Half-wave pulsating dc
The cathode makes thisthe positive end of the load.
A series rectifier diode changes ac to dc.
58
+
-
0
Full-wave pulsating dc
+
-
0
ac
The cathodes make thisthe positive end of the load.
Two diodes and a transformer provide full-wave rectification.
59
VLOAD is equalto one-half thetotal secondary
voltage.
C.T.
½ VTOTAL
VTOTAL
Only half of the transformer secondary conducts at a time.
60
+
-
0
Full-wavepulsating dc
+
-
0
ac
The bridge circuit eliminates the need for a transformer.
61
+
-
0 Full-wavepulsating dc
+
-
0
ac
Reversing the diodes produces a negative power supply.
62
Power Supply Basics QuizMost line-operated power supplies change ac to ________. dc
A single diode achieves ________ -wave rectification. half
Two diodes and a center-tapped transformerprovide ________ -wave rectification. full
A bridge rectifier uses ________ diodes. four
The positive end of the load is the end in contact with the diode ________. cathodes
63
Vac
Vdc
ac
Vac
Vdc
Ignoring diode loss,the average dc is 45%
of the ac input forhalf-wave.
Vac
Vdc
Converting rmsto average
64
Vac
Vdc
ac
Vac
Vdc
Ignoring diode loss,the average dc is 90%
of the ac input forfull-wave.
65
0 V
-200 V
+200 V
20 ms 40 ms0 ms
3 120 V60 Hz
Three-phase rectification is used in commercial,industrial and vehicular applications.
Full-wave, 3 bridge
Vdc = 1.35 x Vrms = 162 V
66
10 20 30 400
Time in milliseconds
40
80
120
160
200
0
Vol
tsThree-phase rectifier output
Vdc = 1.35 x Vrms = 162 V
67
Average dc QuizThe average dc voltage with half-wave isequal to ______ of the ac voltage. 45%
The effective ac voltage in a two-diode, full-wave rectifier is _______ of the secondary voltage.
half
The average dc voltage with a full-waverectifier is _________ of the effective ac voltage.
90%
The average dc voltage with a bridge rectifieris equal to ________ of the ac voltage. 90%
The average dc voltage with a 3 bridge rectifier is equal to ________ of the ac voltage. 135%
68
Filtercapacitor
+
-
0
Charge
Discharge
VP
A relatively large filter capacitor will maintain theload voltage near the peak value of the waveform.
ac
69
ac
+
-
0
Discharge time is less.
Full-wave is easier to filter since the discharge time is shorter than it is for half-wave rectifiers.
VP
70
Adding a filter capacitorincreases the dc output
voltage.
Vac
Vdc
ac
Vac
Vdc
Ignoring diode lossand assuming a largefilter, the dc output is
equal to the peak valuefor both half-wave and
full-wave.
71
Vac
Vdc
Vac
Vdc
ac
Ignoring diode lossand assuming a largefilter, the dc output is
equal to the peak valuefor both half-wave and
full-wave.
72
ac
Vac
Vdc
Full-wave doublerVac
Vdc
Ignoring diode loss andassuming large filters,
the dc output is twice thepeak ac input.
73
C1 is charged.
C1ac
Half-wave voltage doubler
C2
The charge on C1 adds to the ac line voltageand C2 is charged to twice the peak line value.
74
Capacitive Filter dc Output Quiz(Ignore diode loss and assume a light load for this quiz.)
The dc output in a well-filtered half-wave supply is _____ of the ac input. 141%
The dc output in a well-filtered full-wave supply is _____ of the ac input. 141%
The dc output in a well-filtered half-wave doubler is _____ of the ac input. 282%
The dc output in a well-filtered full-wave doubler is _____ of the ac input. 282%
75
Vac
Vdc
Vac
Vdc
An ideal dc power supply has no ac ripple.
ac ripple = 0%
76
Vac
Vdc
Vac
Vdc
acac ripple =
12 Vdc
1.32 Vac x 100% = 11 %
Real power supplieshave some ac ripple.
77
Vac
Vdc
An ideal power supply has perfect voltage regulation.
The voltagedoes not change.
78
Vac
Vdc
Vac
Vdc
ac
The output of areal supply drops
under load.
Voltage Regulation =VVFL
x 100 %
= 12 V1 V
x 100 %
= 8.33 %
79
0246
5
10
15
20
25
30
35
Reverse Bias in Volts
ReverseCurrentin mAI
V
Vrev
The voltage across a conductingzener is relatively constant.
81012
80
ac
Vac
Vdc
A shunt zener diode canbe used to regulate voltage.
Vac
Vdc
Vac
Vdc
If the zener stops conducting, the regulation is lost.
81
Power Supply Quality QuizThe voltage regulation of an ideal powersupply is ___________. 0%
The ac ripple output of an ideal powersupply is ___________. 0%
small
The ac component of an ideal dc power supply should be as ________ as is feasible. small
A device that is commonly used to regulatevoltage is the ________ diode. zener
V in a real power supply should be as ___________ as is feasible.
82
REVIEW
• The System• Half-Wave Rectification• Full-Wave Rectification• RMS to Average• Filters• Multipliers• Ripple and Regulation• Zener Regulator
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