Voltage References/ Regulatorsece.tamu.edu/~s-sanchez/457 Voltage_ references_1A.pdf · • The...
Transcript of Voltage References/ Regulatorsece.tamu.edu/~s-sanchez/457 Voltage_ references_1A.pdf · • The...
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Voltage References/RegulatorsPART 1
ECEN 457: Op-Amps and ApplicationsAnalog & Mixed-Signal Center
Texas A&M University
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ECEN 457 (ESS)
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Agenda• Motivation
• Important Definitions
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Voltage Regulator Market
Major Companies:
Texas Instruments
STMicroelectronics
Toshiba
Maxim
Linear Technologies
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Voltage References/Regulators• The function of a voltage reference/regulator:
– Provide stable dc voltage Vo starting from a
less stable voltage Vi
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Basic connection of a voltage reference/regulator
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Voltage References• Voltage reference:
– Provides an even more stable Vo to serve as a standard for other circuits.
– Application:• Digital multimeter: the full-scale accuracy is set by the internal
voltage of suitable quality.
– Other applications:• Power supplies• AD/DA converters• V-F / F-V converters
– Main requirements:• Accuracy • Stability
– To minimize errors due to self-heating:• Modest output-capabilities (few mA)
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Voltage Regulators• VI is usually a poorly specified voltage
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V
Battery (VI)
Regulated Voltage(VL)
Time
Battery DC-DC converter
Voltage
Regulator
+
-
Load
+
-
VL
VI
E.g. Ipod
Requirements:
• Similar to voltage references but less stringent
• Output current capabilities are much higher (100mA-10A)
AC-DC converter DC-DC converter
E.g. Computer
VI
t t
VI VL
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Voltage Regulators
– Two Types:
• Linear regulators
– Simple
– Low noise
– Poor Efficiency
• Switching regulators
– High efficiency
– Output voltage can be:
» Negative
» Higher than VI
– Complex
– Require inductors
– Noisier
Voltage Reference
Control Element
Error Amplifier
Feedback Network
Feedback Network
Output Filter
Load
Power Switch
Modulator
Voltage Reference
Error Amplifier
Load
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Important Definitions
• Line Regulation:
• Load Regulation:
o
o
I
VregulationLoad
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I
o
V
VregulationLine
oI
o
VV
VregulationLine
100(%)
o
o
o
I
VV
regulationLoad
100%
ILOAD
VOUT(LT)
VOUT(LR)
VIN
VOUT(LT)
VOUT(LR)
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More Definitions
• Ripple ( power supply) rejection ratio (RRR) (PSR):
• Dropout Voltage:
– The minimum difference between VI and Vo for which the circuit still operates properly.
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ro
ridB
V
VRRR 10log20
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Example 11.1
• The data sheets of the uA7805 5-V voltage regulator (Fairchild) indicate that Vo typically changes by 3mV when VI is varied from 7 V to 25 V, and by 5 mV when Io is varied from 0.25 A to 0.75 A. Moreover, RRRdB = 78dB at 120 Hz.
– Estimate the typical line and load regulation of this device. What is the output impedance of the regulator?
– Estimate the amount of output ripple Vro for every volt of Vri.
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VmV
V
V
I
o /17.0725
103 3
VxV
VmV
V
V
I
o /%0033.01005
/17.0(%)
AmV
I
V
o
o /1025.075.0
105 3
riri
ro VV
V 3
)20/78(10126.0
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mVVro 126110126.0 3 For 1-V at 120Hz ripple at the input:
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More Definitions
• Thermal Coefficient of Vo:
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T
VVTC o
o
)(
o
oo
VT
VVTC
100)(%)(
o
oo
VT
VppminVTC
610)(
ppm = parts per million
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Example 11.2
• The data sheets of the REF101KM 10-V precision voltage reference (Burr-Brown) give a typical line regulation of 0.001%/V, a typical load regulation of 0.001%/mA , and a maximum TC of 1 ppm/C. Find the variation in Vo brought about by: (a) a change of VI from 13.5 V to 35V; (b) a 10mA change in Io ; (c) a temperature change from 0 C to 70 C.
– (a)
– (b)
– (c)
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105.1335
100/%001.0 oVV
mVVo 15.2
1010
100/%001.0 oV
mAmA
mVVo 1
1070
10/1
6
oV
CCppm
mVVo 7.0
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More Definitions
• Efficiency
)( OUTQIN
OUTOUT
IN
OUT
IIV
IV
P
P
If IQ<< ILOAD
%1.891007.3)100100(
3.3100max
AmA
mA
Example: A 3.3 V linear regulator with 3.7 V < VIN < 4.7 V, IQ = 100 μA
1 mA < Io < 100 mA. What is the minimum drop-out voltage? What is the
maximum efficiency? What is the minimum efficiency?
%8.631007.4)1001(
3.31min
AmA
mA
IN
DO
IN
DOIN
IN
OUT
V
V
V
VV
V
V 1
%2.891007.3
4.01max
V
or
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Next Class
• Bandgap voltage reference
• Voltage regulators
– Shunt voltage regulators
– Linear regulators