Today
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2/22/11 Physics 262 Lecture 6
Power Supplies and Regulators
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Transformers
Rectifiers
Power supplies and regulators
Reading
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Reread 28-29 (1.17) and 44-48 (1.25-1.29)
Read 52 (1.31), 307-311 (6.01-6.02) and 325-333
Homework due 3/1
1.
2.
3.
4.
•
Exercises 1.27 (p. 46), 6.1 (p. 311), and chapter 6 additional exercise 1 ( p. 384)
Choose a filter capacitor BFPS supplied by a 10:1 transformer with 120 Vrms input voltage to the
transformer has less than 0.5V peak to peak ripple.
A 1:2 transformer is supplied with Vrms =120V input and has a 1k ohm load. What are the power
dissipated into load, the RMS voltage on load, and the peak current in the primary and the
secondary coils?
The typical line AC voltage of Vrms =120V followed by with a 1:20 turn ratio transformer supplies a
BFPS (with typical 0.6V diodes) and 500 ohm load and 1mF capacitor. What is the output ripple?
Lab
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Lab 5 Power supplies
Do pre-lab BEFORE lab
Lab 4 write-up due Friday at 10am
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 1
Transformer
.
Vin
N1
N2
Rload
Primary
Coil
Pout  Pin
N2
Turn Ratio 
N1
Secondary
Coil
iout
N1
iin

N2
A.k.a N2:N1
Vout
N2
Vin

N1
Vin
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Vout
Page 2
Bridge Rectifier
1
+
V1
.
C1
Vout
D4
10:1
D2
3
D1
2
i
D1
4
T1
.
D3
i
Rload
iload
-
Positive half-cycle: Current flows through D1, Rload and D3
Negative half-cycle: Current flows through D2, Rload and D4
Note in both directions, there are two diode voltage drops
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 3
Charging
Current
Brute Force Power Supply
Filtered
Output
Voltage
1
+
C1
.
D4
10:1
ic
Vout
D1
4
V1
3
D2
2
D1
T1
.
Unfiltered
output
from
Bridge
D3
ic
Rload
iload
-
Note polarity of
Charging Current
electrolytic capacitor
The output is the amplitude of the input, divided by the turns ratio of the
transformer minus drop across the rectifier diodes.
VOut _ max  ( N 2 / N1 )VAC _ in _ max  2Vdiode
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 4
Ripple Voltage
Output
Voltage
Vripple
Vbfps
VDC _ max
Rload
18Vdc
t
0
For small ripple, VDC ~ VDC_max
BFPS has filter
capacitor, C
dV
iC
dt
Vbfps
Rload
18Vdc
0
Vripple
it VDC t


C
RC
1
Let RLOAD  1k , t 
, C  1000 F
120 Hz
18V
Vripple 
 0.15VDC
1201k 1000 F
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 5
Load and Line Regulation
load regulation
“Change in output voltage or current for any load change
within ratings”
line regulation:
“Change in output voltage or current for any line change
within ratings.”
Based with permission on lectures by John Getty
BFPS has Poor Load Regulation
Parasitic resistance associated with the elements in the circuit all
contribute to a relatively large Thévenin equivalent resistance.
16
14
Thévenin Equivalent
Output Voltage
12
R1
10
2ohm
8
V1
6
15V
4
2
0
1E-1
1E+0
1E+1
1E+2
1E+3
1E+4
1E+5
1E+6
Load Resistance
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 7
BFPS has Poor Line Regulation
Changes in line voltage propagate directly through to the load.
T1
.
V1
3
2
1
+
C1
.
Vout
Rload
10:1
4
D1
-
VDC _ out  VAC _ line  Tratio  2Vdiode
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 8
Summary of BFPS Characteristics
T1
.
V1
3
2
1
+
C1
.
Vout
Rload
10:1
4
D1
• Large ripple voltage amplitude
-
“Bulk” DC
• Poor line and load regulation
• High current capacity (“ampacity”)
• Inexpensive
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 9
Regulated DC Supply
BFPS
Reference
(V or I)
Error
Amplifier
Pass
Element
Filter
Load
Regulator
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 10
Basic Positive Linear Regulator
Vbfps
Rv_ref
1
Error_Amp
3
Ref_Zener
Pass_Transistor
2
Rcl
Load
Current_Limit
Filter
Reference
Voltage
Pass Element
•BFPS powers zener, amp, and trans
•Zener produces Vref => Vin+
•R1 & R2 scales Vout for input to Vin•Error amp adjusts pass trans
Vout
Error Amp
R1
Rload
•Current limited by V across Rcl
C_filter
•C_filter helps get rid of ripple
•Vout independent of Rload, to a point
•
•
R2
Small output ripple
Pass element in regulator dissipates energy
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 11
Vref nominally is 7.15V
But ranges from 6.8 to 7.5V
Pass
Element
723 Regulator
13
12
11
4
6
10
5
Error Amp
Reference Voltage
No Connection
Pins 1, 8 and 14
7
9
2
3
Vreg max is 37V
Vc > V reg + 3 V
and Vc > 9.5V to power reference
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 12
12
4
Vcc
LM723 Regulator
11
TP1
Vout
10
5
Q1
TIP31
Error Amp
7
Vilim
LM723
9
2
3
Pass
Trans
10
Vz
9
•BFPS supplies Pass Trans and 723
•R2 & R3 scale Vreg for input to VinFor Vref > Vout > 2V, divide Vref down
VOUT
U1
IN+
IN-
VZ
COMP
VREF
ILIM
ISENSE
•Vref goes into Vin+
•723 Vout turns on power Pass Trans
Vref
VC
V+
V-
R1
1.5
Rcl
5
4
10W, 10%
C2
1n
13
6
Vreg
1
6
From BFPS
1
13
Pass
Element
723 Regulator Plus Power Pass Transistor
2
3
11
12
7
R2
TBD
GND
•Power pass trans supplies current to Vreg
0
•Add C_filter of 0.01-0.1uF ceramic and 1-10uF electrolytic
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Vin-
R3
TBD
1
•Pass Trans current limited by voltage across Rcl
Set for 0.5V across Rcl at max current.
TP5
0
Page 13
TP7
CV and CC Modes
5Vdc Source
IV diagrams
10
Amps
DC voltage source
0
-10
-10
0
10
Volts
5Adc Source
10
Amps
DC Current Source
0
-10
-10
0
10
Volts
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 14
Practical Voltage/Current Source
Most laboratory supplies will “fold back” from constant
voltage mode into constant current as required by the
load. The point at which the supply converts from
constant voltage to constant current is often controllable.
Ideal CV supply can source infinite
current.
Practical CV supply is generally
protected by limiting output power.
Could include “crowbar.”
constant voltage
amps
Lab source folds back at the current
limit set point, and is then said to be
operating in “constant current” mode.
constant current
volts
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 15
References
1.
Paul Horowitz and Winfield Hill (1989). “The Art of Electronics,” 2nd
Ed., Cambridge
2.
3.
4.
Roland E. Thomas and Albert J. Rosa (1998). “The Analysis and
Design of Linear Circuits,” 2nd Ed., Prentice Hall
Abraham I. Pressman (1998). “Switching Power Supply Design,” 2nd
Ed., McGraw-Hill
Service Guide Agilent E3631A DC Power Supply
http://cp.literature.agilent.com/litweb/pdf/E3631-90011.pdf
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 16
Load Regulation
load re·gu·la·tion
1.
“Change in output voltage or current for any load
change within ratings”
2.
±(% of output + offset)
vline = 115 +/- 10% VAC
Load Regulation for the Agilent E3631A:
Voltage <0.01% + 2 mV
vout  25V
v  vout0.0001  2mV
Current <0.01% + 250 A
vmin  vout  v
vmin  24.995 V
Output Ratings (@ 0 °C - 40 °C)
vmax  vout  v
vmax  25.005 V
+6V Output 0 to +6 V ; 0 to 5 A
+25V Output 0 to +25 V ; 0 to 1 A
-25V Output 0 to -25 V ; 0 to 1 A
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 17
Line Regulation
line re·gu·la·tion:
1.
2.
“Change in output voltage or current for any line
change within ratings.”
“bedding
material
for a large member of
±(%
of output
+ offset)
the feline genus”
vline = 115 +/- 10% VAC
Line regulation for the Agilent E3631A:
Voltage <0.01% + 2 mV
Current <0.01% + 250 A
AC Input Rating (line): 115Vrms ±10%
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 18
Power Supply Terminology I
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 19
Power Supply Terminology II
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 20
Power Supply Terminology III
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 21
Power Supply Terminology IV
Physics 262 Laboratory Electronics II Spring 11 Lecture 6
Based with permission on lectures by John Getty
Page 22