electronics principles & applications fifth edition chapter 4 power supplies ©1999...
TRANSCRIPT
ElectronicsElectronics
Principles & ApplicationsPrinciples & ApplicationsFifth EditionFifth Edition
Chapter 4Power Supplies
©1999 Glencoe/McGraw-Hill
Charles A. Schuler
• The System• Half-Wave Rectification• Full-Wave Rectification• RMS to Average• Filters• Multipliers• Ripple and Regulation• Zener Regulator
INTRODUCTION
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.
ac Power Supply
Circuit A
Circuit B
Circuit C
dc
dc
dc
Most line operated supplies change ac to dc.
+
-
0
+
-
0ac
A series rectifier diode changes ac to dc.
Half-wave pulsating dc
The cathode makes thisthe positive end of the load.
+
-
0
Full-wave pulsating dc
+
-
0
ac
Two diodes and a transformer provide full-wave performance.
The cathodes make thisthe positive end of the load.
VLOAD is equalto one-half thetotal secondary
voltage.
C.T.
One-half of the transformer secondary conducts at a time.
VTOTAL
VTOTAL
+
-
0
Full-wave pulsating dc
+
-
0
ac
The bridge circuit eliminates the need for a transformer.
+
-
0
Full-wave pulsating dc
+
-
0
ac
Reversing the diodes produces a negative power supply.
Power supply basics quiz
Most line-operated power supplies changeac to ________. dc
A single diode achieves ________ -waverectification. 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 incontact with the diode ________. cathodes
Vac
Vdc
ac
Vac
Vdc
Ignoring diode loss,the average dc is 45%
of the ac input forhalf-wave.
Vac
Vdc
Converting rmsto average
Vac
Vdc
ac
Vac
Vdc
Ignoring diode loss,the average dc is 90%
of the ac input forfull-wave.
Average dc quiz
The 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%
Filtercapacitor
+
-
0
Charge
Discharge
VP
A relatively large filter capacitor will maintain theload voltage near the peak value of the waveform.
ac
ac
+
-
0
Discharge time
Full-wave is easier to filter since the discharge time is shorter than it is for half-wave rectifiers.
VP
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.
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.
ac
Vac
Vdc
Full-wave doublerVac
Vdc
Ignoring diode loss andassuming large filters,
the dc output is twice thepeak ac input.
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 value.
Capacitive filter dc output quiz(assume a very 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%
Vac
Vdc
Vac
Vdc
An ideal dc power supply has no ac ripple.
ac ripple = 0%
Vac
Vdc
Vac
Vdc
acac ripple =
12 Vdc
1.32 Vac x 100% = 11 %
Real power supplieshave some ac ripple.
Vac
Vdc
An ideal power supply has perfect voltage regulation.
The voltagedoes not change.
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 %
ac
Vac
Vdc
A zener diode canregulate voltage.
Vac
Vdc
Vac
Vdc
But, if the zener stops conducting, the regulation is lost.
Power supply quality quiz
The 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 supplyshould 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.
REVIEW
• The System• Half-Wave Rectification• Full-Wave Rectification• RMS to Average• Filters• Multipliers• Ripple and Regulation• Zener Regulator