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Transcript 
BE Lesson 11: AC to DC power supply
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What is an AC to DC power supply?
What is a rectifier?
What is an RC filter?
What is a regulator?
© 2012 C. Rightmyer, Licensed under The MIT OSI License, 20 July 2012
What’s a AC to DC adapter?
Sometimes called a DC power supply?
AC voltage and current go both positive and negative
I = Imax sin q
[Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960]
Power supply design requirements
35. 0 v
V o DC
1. 2 v
ACV
in
Step down
transformer
Pulsating
DC rectifier
Transformer AC output
designed to support
power supply maximum
DC output voltage
Capacitive
filter
Voltage
regulator
DCV out
Full wave rectifier and its output voltage pattern
+12 V AC
120 V
AC
-12 V AC
[Building Power Supplies, Master Publishing Inc, David Lines, 1991
How does a diode operate in a circuit?
+
-
Forward voltage drop ~ 0.7 volts
Maximum reverse voltage = 50 volts
Adapted from http://www.kpsec.freeuk.com/components/diode.htm
Smoothing the output with an RC filter
[Building Power Supplies, Master Publishing Inc, David Lines, 1991
Ripple voltage after RC filtering
[Building Power Supplies, Master Publishing Inc, David Lines, 1991
BE demo 11-1 (a). AC Sinewave voltage pattern
6 VAC
6 VAC
Center Tapped
Transformer
120 VAC
Oscilloscope
BE demo 11-1 (b). AC Sinewave voltage pattern
6 VAC
Center Tapped
Transformer
120 VAC
Oscilloscope
1K
1N4001
BE demo 10-1 (c). Pulsed DC voltage pattern.
Center Tapped
Transformer
120 VAC
Oscilloscope
1K
1N4001
1N4001
BE demo 11-1 (d). Smoothed Pulsed DC voltage
470 uF
1N4001
12 VAC
Center Tapped
Transformer
120 VAC
Oscilloscope
1K
1N4001
BE demo11-1 (e). Measured DC output voltage
1K
1N4001
12 VAC
Center Tapped
Transformer
120 VAC
470 uF
1N4001
8.5 volts
DC
Voltmeter
BE demo 11-1 (f). Regulated 5 volt output
UA7805
1K
1N4001
12 VAC
Center Tapped
Transformer
120 VAC
470 uF
5 vDC output
1N4001
5 volts
DC
Voltmeter
BE demo 11-2. An Improved DC power supply with adjustable DC
output voltage
LED
R1
D1
T1
120
VAC
12
VAC
In
12
VAC
LM
317
Out
R2
Adj
D2
T1: 24v secondary, 2 amps
D1, D2: 1N5400
R1: 220, 1/4 watt
R2: 240, 1/4 watt
R3: 5k pot, 1/2 watt
C1, C2: 2200uf, 50v
C3: 0.1uf, 50v
C1
C2
C3
Vo
R3
317
Adj
In
Out
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