Tài liệu Power Supply Block Diagram ppt

Power Supply Block DiagramPower Supply Block Diagram
H. Chan; Mohawk College
1
HalfHalf--Wave RectifierWave Rectifier
7.0V2V
SP
−=
⎟
⎟
⎞
⎜
⎜
⎛
−=
Pd
00833.0
1VV
V
⎟
⎠
⎜
⎝
FL
Pdc
CR
V00480
FL
P
r
CR
V0048.0

V =
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FL
t
FullFull--Wave RectifierWave Rectifier
7.0V707.0V
sP
−=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−=
Pdc
CR
00417.0
1VV
V
⎟
⎠
⎜
⎝
FL
Pdc
CR

V00240
V
FL
P
r
CR
V0024.0
V =
t
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FL
CR
t
BridgeBridge--Type RectifierType Rectifier
4.1V2V
sP
−=
⎟
⎟
⎞
⎜
⎜
⎛
−=
Pdc
00417.0
1VV
V
⎟

⎠
⎜
⎝
FL
Pdc
CR
V00240
V
FL
P
r
CR
V0024.0
V =
t
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FL
CR
t
More Equations . . . More Equations . . .
Rithi ti
V V + 1 736 V
Rearranging the previous equations:
V
P
= V
dc
+ 1.736 V
r

The ripple voltage as a percentage of the dc voltage is:
V
100% x
V
V
ripple
dc
r
=
The diode(s) must be rated to withstand the surge current:
P
V
where R
W
is the transformer winding’s
W
P
surge
R
V
I =
W
g
resistance given by:
FLNL
W
I
VV
R
−

=
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FL
I
Comparison of Different Types of RectifiersComparison of Different Types of Rectifiers

Half-wave rectifier needs only a single diode but
ripple is twice those of the other types.
ll ifi i d

Full-wave rectifier requires a centre-tapped
transformer and its output voltage is about half
those of the other types.those of the other types.

Bridge-type rectifier is best overall even though
it requires four diodes because the diode bridge is
often available in a single package. However, if
a single diode in the bridge is defective, the
whole package has to be replaced
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whole package has to be replaced.
Line RegulationLine Regulation
is a measure of the effectiveness of a voltage regulatoris a measure of the effectiveness of a voltage regulator
to maintain the output dc voltage constant despite
chan
ges in the supply voltage.
o
V

VmVregulationLine
Δ
=)/(
gppyg
i
V
VmVregulationLine
Δ
)/(
i
o
V
x
V
V
regulationline
100
%
Δ
Δ
=
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oi
VVΔ
Load RegulationLoad Regulation
i f th bilit f l t t i t iis a measure of the ability of a regulator to maintain a
constant dc output despite changes in the load current.
o
I

V
AmVregulationLoad
Δ
Δ
=)/(
L
I
g
Δ
)(
V
100
Δ
oL
o
V
x
I
V
regulationload
100
%
Δ
Δ
=
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Other SpecificationsOther Specifications
A d fi iti f lt l ti iA common definition for voltage regulation is:
100(%) x

VV
regulationVoltage
FLNL
−
=()
V
gg
FL
The ability to reduce the output ripple voltage is:
)(
)(
log20)(
inr
outr
V
V
dBrejectionRipple −=
)(inr
Source resistance of regulator is:
ΩΩ
Δ
Δ
= mor
I
V
R
o
s
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g
ΔI
L
Zener Diode Voltage RegulatorZener Diode Voltage Regulator
I-V Characteristic
Circuit
I
ZM
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ZM
Notes on Zener Diode RegulatorNotes on Zener Diode Regulator

V
Z
depends on I and temperature.

Zener diodes with rated voltage < 6 V have
i ffi i h dnegative temperature coefficient; those rated > 6
V have positive temperature coefficient.

In order to maintain a constant V I varies in

In order to maintain a constant V
o
, I
ZT
varies in
response to a change of either I
L

or V
i
. For
example, when R
L
increases, I
L
decreases, then
I
ZT
has to increase to keep the current through R
s
constant. Since the voltage drop across R
s
is
constant V stays constant
H. Chan; Mohawk College
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constant, V
o
stays constant.
Formulae for Zener Regulator CircuitFormulae for Zener Regulator Circuit
R establishes the zener bias current I :R
s
establishes the zener bias current, I
ZT
:
ZiZi
s
II

VV
I
VV
R
+
−
=
−
=
LZTRs
III +
For fixed V
i
, but variable R
L
:
Zi
Zs
Rs
Z
L
VV
VR
I
V
R
−
==.min
ZZ
L

ZiRs
II
V
I
V
R
−
==.max
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ZMRsL
III
(min)
Formulae (cont’d)Formulae (cont’d)
FfidRbt iblVFor fixed R
L
, but variable V
i
:
Z
sL
i
V
R
RR
V
+
=.min
ZsRi
Z

L
i
VRIV
R
+=
(max)
.max
LZMR
IIIwhere +=
(max)
The output ripple voltage of the zener regulator is:ppp g g
)()(
//
//
inr
ZL
outr
V
RRR
RR
V
+
=
where R
Z
= ac resistance
of zener diode
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//

sZL
RRR +
of zener diode.
Transistor Series Voltage RegulatorTransistor Series Voltage Regulator
The simple zener regulatorThe simple zener regulator
can be markedly improved
by adding a transistor.
Since V
BE
= V
Z
-V
L
any
tendency for V
L
to decrease
or increase will be negatedor increase will be negated
by an increase or decrease in I
E
. The dc currents for the
circuit are:
VV
VVV
−
−
circuit are:
R
VV
I

R
VV
R
V
I
Zi
R
L
BEZ
L
L
L
−
=
−
== ;
I =h I ;I =I I
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I
L
= h
FE
I
B
; I
ZT
= I
R
- I

B
Transistor Shunt Voltage RegulatorTransistor Shunt Voltage Regulator
Since V =V VSince V
BE
= V
L
- V
Z
,
any tendency for V
L
to increase or decrease
will result in a
corresponding increase or decrease in I
Rs
. This will
oppose any changes in V
L
because V
L
= V
i
-I
Rs
R
s
.
BEZiBEZL
)VV(V
I

VVV
I
+−+
S
BEZi
Rs
L
BEZ
L
L
L
R
)(
I;
RR
I ===
I = I - I = h I
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I
E
I
Rs
- I
L
h
FE
I
ZT
OpOp--Amp Voltage RegulatorsAmp Voltage Regulators

h
Z
V
R
V
⎟
⎟
⎞
⎜
⎜
⎛
+≅
2
1
Series
Shunt
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Zo
V
R
V
⎟
⎟
⎠
⎜
⎜
⎝
+≅
3

1
Notes on OpNotes on Op--Amp Voltage RegulatorAmp Voltage Regulator

More flexibility possible in design of voltage
output than IC voltage regulator packages.
hiliil

The essential circuit elements are: a zener
reference, a pass or shunt transistor, a sensing
circuit, and an error/amplifier circuit.circuit, and an error/amplifier circuit.

Equation indicates that V
o
depends on R
2
, R
3
,
and V
Z
.

The shunt configuration is less efficient but R
2
offers short-circuit current limiting.
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Constant Current LimitingConstant Current Limiting
can be used for short-circuit or overload protection ofcan be used for short circuit or overload protection of
the series voltage regulator.

Ot t tOutput current
is limited to:
4
(max)
7.0
R
I
L
=
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FoldFold--back Current Limitingback Current Limiting
is a better method of short-circuit protection.is a better method of short circuit protection.
LBBE
VRIV
R
VVV −+=−= )(
4
6
22
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oLooBBE
VRIV
RR
VVV +
+
)(
4
65

22
Design Equations for FoldDesign Equations for Fold--back Current Limitingback Current Limiting
Maximum load current without fol
d-back limiting:g
655
(max)
)(7.0
RR
RRVR
I
o
L
++
=
64
RR
Output voltage under current limiting condition:
RRR )(70 +
L
L
o
RRRR
RRR
V
564
65
)(7.0
'
−
+

=
The short circuit current (i e when V =0)is:The short circuit current (i.e. when V
o
= 0) is:
65
)(7.0
RR
RR
I
short
+
=
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64
RR
short
Characteristics of FoldCharacteristics of Fold--back Limitingback Limiting
V

Notice that I
short
< I
L(max)
and that V
o
is regulated
(i.e. constant) only after
V
o

(i.e. constant) only after
R
L
> a certain critical
value.

For designing purpose
I

For designing purpose,
R
5
+ R
6
= 1 kΩ and if
I
short
and I
L(max)
are
specified then
I
L
specified then
4
70)70(
07
o
IVI
V

R
−+
=
H. Chan; Mohawk College
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(max)
7.0)7.0(
Loshort
IVI −+
Transistor Current RegulatorsTransistor Current Regulators
are designed to maintain a fixed current through agg
load for variations in either V
i
or R
L
.
For the BJT circuit V =V VFor the BJT circuit, V
EB
= V
Z
- V
RE
.
Any tendency for I
L
to change will
cause an o
pposing change in V
EB
,pp g g

EB
,
thus nullifying the perturbation.
For the JFET circuit, I
L
= I
D
= I
DSS
as
long as V
L
< V
SS
-V
P
.
H. Chan; Mohawk College
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IC Voltage RegulatorsIC Voltage Regulators

There are basically two kinds of IC voltage
regulators:
 Multipin type, e.g. LM723C
 3-pin type, e.g. 78/79XX

Multipin regulators are less popular but they
provide the greatest flexibility and produce the
highest quality voltage regulationhighest quality voltage regulation


3-pin types make regulator circuit design simple
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Multipin IC Voltage RegulatorMultipin IC Voltage Regulator

The LM723 has an
equivalent circuit that
contains most of thecontains most of the
parts of the op-amp
voltage regulator
discussed earlier.discussed earlier.

It has an internal voltage
reference, error
amplifier pass transistor
LM 723C S h i
amplifier, pass transistor,
and current limiter all in
one IC package.
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LM 723C Schematic
Notes on LM723 Voltage RegulatorNotes on LM723 Voltage Regulator

Can be either 14-pin DIP or 10-pin TO-100 can

May be used for either +ve or -ve, variable or
fi d l d lfixed regulated voltage output

Using the internal reference (7.15 V), it can

operate as a high voltage regulator with outputoperate as a high-voltage regulator with output
from 7.15 V to about 37 V, or as a low-voltage
regulator from 2 V to 7.15 V

Max. output current with heat sink is 150 mA

Dropout voltage is 3 V (i.e. V
CC
> V
o(max)
+ 3)
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