Transcript Chapter 4

Electronics
Principles & Applications
Fifth Edition
Charles A. Schuler
Chapter 4
Power Supplies
©1999
Glencoe/McGraw-Hill
INTRODUCTION
• The System
• Half-Wave Rectification
• Full-Wave Rectification
• RMS to Average
• Filters
• Multipliers
• Ripple and Regulation
• Zener Regulator
Circuit A
Power Supply
Circuit B
Circuit C
The power supply energizes the other circuits in a system.
Thus, a power supply defect will affect the other circuits.
dc
ac
Power Supply
Circuit A
dc
Circuit B
dc
Circuit C
Most line operated supplies change ac to dc.
The cathode makes this
the positive end of the load.
+
0
-
+
ac
0
Half-wave pulsating dc
A series rectifier diode changes ac to dc.
The cathodes make this
the positive end of the load.
+
0
Full-wave pulsating dc
+
0
ac
-
Two diodes and a transformer provide full-wave performance.
One-half of the transformer secondary conducts at a time.
C.T.
VTOTAL
 VTOTAL
VLOAD is equal
to one-half the
total secondary
voltage.
+
0
-
ac
+
0
Full-wave pulsating dc
The bridge circuit eliminates the need for a transformer.
+
0
-
ac
+
0
Full-wave pulsating dc
Reversing the diodes produces a negative power supply.
Power supply basics quiz
Most line-operated power supplies change
ac to ________.
dc
A single diode achieves ________ -wave
rectification.
half
Two diodes and a center-tapped transformer
provide ________ -wave rectification. full
A bridge rectifier uses ________ diodes.
four
The positive end of the load is the end in
contact with the diode ________. cathodes
Vac
Vac
Vdc
Vdc
Ignoring diode loss,
the average dc is 45%
of the ac input for
half-wave.
ac
Converting rms
to average
Vac
Vdc
Vac
Vdc
ac
Ignoring diode loss,
the average dc is 90%
of the ac input for
full-wave.
Vac
Vdc
Average dc quiz
The average dc voltage with half-wave is
equal 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-wave
rectifier is _________ of the
effective ac voltage.
90%
The average dc voltage with a bridge rectifier
is equal to ________ of the ac voltage. 90%
Filter
capacitor
Discharge
VP
+
ac
0
Charge
-
A relatively large filter capacitor will maintain the
load voltage near the peak value of the waveform.
Discharge time
+
ac
0
-
Full-wave is easier to filter since the discharge
time is shorter than it is for half-wave rectifiers.
VP
Vac
Vdc
ac
Adding a filter capacitor
increases the dc output
voltage.
Ignoring diode loss
and assuming a large
filter, the dc output is
equal to the peak value
for both half-wave and
full-wave.
Vac
Vdc
Vac
Vdc
Ignoring diode loss
and assuming a large
filter, the dc output is
equal to the peak value
for both half-wave and
full-wave.
ac
Vac
Vdc
Vac
Vdc
ac
Full-wave doubler
Ignoring diode loss and
assuming large filters,
the dc output is twice the
peak ac input.
Vac
Vdc
The charge on C1 adds to the ac line voltage
charged.to twice the peak value.
and CC21isischarged
ac
C1
C2
Half-wave voltage doubler
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
An ideal dc power
supply has no ac ripple.
ac ripple = 0%
Vac
Vdc
Vac
Vdc
ac
Real power supplies
have some ac ripple.
1.32 Vac
x 100% = 11 %
ac ripple =
12 Vdc
Vac
Vdc
An ideal power supply has perfect voltage regulation.
The voltage
does not change.
Vac
Vdc
Voltage Regulation =
=
ac
DV
VFL
x 100 %
1V
x 100 %
12 V
= 8.33 %
The output of a
real supply drops
under load.
Vac
Vdc
A zener diode can
regulate voltage.
Vac
Vdc
ac
But, if the zener stops conducting, the regulation is lost.
Power supply quality quiz
The voltage regulation of an ideal power
supply is ___________.
0%
The ac ripple output of an ideal power
supply is ___________.
0%
DV in a real power supply should be
as ___________ as is feasible.
small
The ac component of an ideal dc power supply
should be as ________ as is feasible. small
A device that is commonly used to regulate
voltage is the ________ diode.
zener
REVIEW
• The System
• Half-Wave Rectification
• Full-Wave Rectification
• RMS to Average
• Filters
• Multipliers
• Ripple and Regulation
• Zener Regulator