Download - Chap 7 Voltage Regulators
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Welcome
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Voltage Regulators
2. Performance measures of voltage regulators
1. Introduction
3. Voltage Regulator circuits
(i) Zener Diode Regulator
(ii) Emitter Follower Regulator
(iii) Feedback Voltage Regulator
(iv) Feedback Voltage Regulator using Op-amp
4. Short Circuit Protection
5. Foldback Current Limiting
6. Thermal Shutdown
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Introduction
Fig 7.1 (a) Block diagram of ac to dc converter
Fig 7.1 (b) Block diagram of dc to dc converter
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2. Performance measures of voltage regulators
The factors for poor regulation are:
(i) The line voltage changes and the ripple content in the dc voltage
(ii) The voltage drop across the internal resistanceof the regulator due to load current changes
(iii) The temperature dependence of the device parameters which caused change in the output voltage
TS IR VSV
as defined becan regulator a of tageoutput volin change The
TLoiVo
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2. Performance measures of voltage regulators
TS IR VSV
as defined becan regulator a of tageoutput volin change The
TLoiVo
0,0 TIi
ov
L
V
VS
0,0 TVL
oo
i
I
VR
0,0 Li IV
oT
T
VS
where Sv is the voltage stability factor, Ro is the output resistance and ST is the temperature coefficient
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Fig 7.2 Voltage variations in ideal and practical regulators with load current
2. Performance measures of voltage regulators
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3. Voltage Regulator Circuits
(i) Zener Diode Regulator
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Zener Diode Regulator
The zener diode voltage VZ remains almost constant in the breakdown region so long as
(max)(min) zzz III
Z
Zz(max) Zz(max)
V
PI diode,zener theofP ratingpower by the decided is I where
z
zz
ΔI
ΔVr ,resistancezener finite a has diodezener practicalA
Vz. source, oltageconstant v a as acts diodezener idealAn
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The value of Rs is selected such that it fulfill the following requirements:
1) When the input voltage is minimum and load current is maximum, Iz is sufficient to keep the zener diode under breakdown region.
2) When the input voltage is maximum and the load current is maximum, the zener diode current must not exceed the maximum value(Iz(max)).
Zener Diode Regulator
The optimum value of Rs can be found using the following equations:
(max)
(min)
(min)
(min)
(max)
(max)
L
s
zin
z
L
s
zin
z
IR
VVI
IR
VVI
(max)(min)
(min)
(max)
(min)(max)
(max)
(min)
andLz
zin
s
Lz
zin
s
II
VVR
II
VVR
Hence Rs should be chosen such that Rs(min) < Rs < Rs(max)
(min)(max) sss RRR
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(i) Zener Diode Regulator
Sv and Ro can be obtained by replacing zener diode by its equivalent zener resistance rz. The values are:
0,0 TIi
ov
L
V
VS
0,0 TVL
oo
i
I
VR
zs
zv
rR
rS zso rRR ||
Disadvantages:
1. The maximum load current is limited to Iz(max) – Iz(min)
2. A large amount of power is wasted in the zener resistance and series resistance.
3. The regulation factor Sv and output resistance Ro are not very low.
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Voltage Regulators
2. Performance measures of voltage regulators
1. Introduction
3. Voltage Regulator circuits
(i) Zener Diode Regulator
(ii) Emitter Follower Regulator
(iii) Feedback Voltage Regulator
(iv) Feedback Voltage Regulator using Op-amp
4. Short Circuit Protection
5. Foldback Current Limiting
6. Thermal Shutdown
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(ii) Emitter Follower Regulator
Vo = Vz - VBE
OCECBBEo VVIIVV
1
)(||rR and z
o
rrRR
RRr
rS xs
sz
zv
where rx – base spreading resistance and r small signal resistance between base and emitter terminals of the transistor
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(iii) Feedback Voltage Regulator
OO
ZO
nVV
R
RRVV
2
2B
2
12
RR1
RV and
2
222
eq
)1(R Therefore
n
rrrR zxB
ib2 and ic2 denote the incremental changes in base and collector currents
eq
O
cR
Vi 2
1
113
O
3
1
)||(R and
rrRR
RR
RS
xeq
eq
eq
v
b22c2
222
2
ii
)1(
and
rrrR
Vni
zxB
O
b
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(iv) Feedback voltage regulator using op-amp
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Voltage Regulators
2. Performance measures of voltage regulators
1. Introduction
3. Voltage Regulator circuits
(i) Zener Diode Regulator
(ii) Emitter Follower Regulator
(iii) Feedback Voltage Regulator
(iv) Feedback Voltage Regulator using Op-amp
4. Short Circuit Protection
5. Foldback Current Limiting
6. Thermal Shutdown
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(iv) Feedback voltage regulator using op-amp contd..
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(iv) Feedback voltage regulator using op-amp contd..
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4. Short Circuit Protection
SC
BEDR
R
VVI
SC
2
SCR
Di
SC IR
VVI
3
2
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5. Foldback Current Limiting
SC
(max)R
6.0 VI L
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6. Thermal Shutdown
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Voltage Regulator ICs
General Purpose Voltage Regulator IC
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Positive low voltage (2 V to 7 V) regulator using IC 723
21
2
RR
RVV refout
21
21
213
||
RR
RR
RRR
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High Voltage (above 7 V) regulator using IC 723
2
11R
RAV
volts115.72
1
R
RVout
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Current limiting and current foldback in 723 circuits
Current limiting Current foldback
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Thermal Shutdown
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Voltage Regulator ICs
General Purpose Voltage Regulator IC
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Positive low voltage (2V to 7V) regulator using IC 723
21
2
RR
RVV refout
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High voltage (above 7V) regulator using IC 723
2
11R
RAV
volts115.72
1
R
RVout
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Current limiting and current foldback in 723 circuits
scsc
sense
RR
V 6.0 I limitingCurrent limit
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Current limiting and current foldback in 723 circuits
V 6.04 regR VV
43
414
RR
RVVR
SCreg IRVV1
)(43
44 SCregR IRV
RR
RV
current knee theis This , )6.0(4
43
sc
reg
reg
SC R
VV
RR
RRI
)6.0(4
43
sc
scRR
RRI
At shirt circuit, Vreg=0, I=Isc. Therefore,
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Current Boosting
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Negative Voltage Regulator
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Fixed Voltage Regulators
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Tracking Voltage Regulator
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Adjustable Voltage Regulator
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Switched Capacitor Voltage Converters
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Voltage Inverter
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Voltage Inverter
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Voltage Inverter
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Voltage Inverter
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Switching Regulators
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Buck Regulator
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Bulk Regulator
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Buck Regulator
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Boost Regulator
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Boost Regulator
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Buck-Boost ( Inverting )Regulator
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Switching IC Regulators
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Inverting Buck-Boost Regulator using LM 2575
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LM 2577 boost regulator
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