SWITCH -MODE POWER SUPPLIES AND SYSTEMS
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Transcript of SWITCH -MODE POWER SUPPLIES AND SYSTEMS
SWITCHSWITCH-MODE-MODE POWER POWER SUPPLIES AND SYSTEMSSUPPLIES AND SYSTEMS
Silesian University of TechnologySilesian University of Technology
Faculty of Automatic Control, Electronics Faculty of Automatic Control, Electronics and Computer Sciencesand Computer Sciences
Ryszard Siurek Ph.D., El. Eng.Ryszard Siurek Ph.D., El. Eng.
Lecture No 7Lecture No 7
ZZp ZZS
TT
DD1
CC RR0 U0UIN
CIN
Flyback converterFlyback converter
TT nZZ
S
p transfer ratiotransfer ratio
exceptional topology comprising transformer and output choke in one magneticexceptional topology comprising transformer and output choke in one magnetic component component
topology with lowest compenet count – cheapest solutiontopology with lowest compenet count – cheapest solution
IIpp
IITT
IIDD II00
IICC
ZZp ZZS
DD1
CC RR0 U0UIN
CIN
TT
IIDD II00
IICC
T IITT
L
Compare to flyback switching regulatorCompare to flyback switching regulator
Flyback converter basic relations analysisFlyback converter basic relations analysis
Cycle I - transistor T is ONCycle I - transistor T is ON
ZZp ZZS
TT
DD1
CC RR0U0
UIN
IITT
II00
IICC
nUIN
IITT
IIpmaxpmax
BB
HH
tLU
(t)ip
TIN
Magnetic energy stored in the coreMagnetic energy stored in the coreBy the end of cycle IBy the end of cycle I 2
ILE
2pmaxp
1
BBSS
Cycle II - transistor T is OFFCycle II - transistor T is OFF
ZZp ZZS
TT
DD1
CC RR0
UIN
IITT=0=0
II00
IICC
0UUp
nU0
IIDD
IIDmaxDmax
BB
HH
BBSS
U0
IIDD
’ ’
TT
Magnetic energy recoveredMagnetic energy recoveredfrom the core by the end of cycle IIfrom the core by the end of cycle II 2
ILE
2Dmax
2S
tLU
I(t)iS
0DmaxD
2IL
2
ILEE
2Dmax
2pmaxp
21S
From energy balance :From energy balance :
(1)(1)
tLU
I(t)iS
0DmaxD (2)(2)
U0
Ro
II0
~~UCLS
IIDmax iiD(t)
From equation (1) :From equation (1) :
2but
S
ppmaxDmax zAlL
L
LII Al - core constantAl - core constant
hence:hence:nI
Z
ZII pmax
ppmaxDmax
S
UU0 0 may be calculated also from energy balance::
2T
RLIUT
RU
2
IL 0ppmax0
0
20
2pmaxp valid only in case of discontinuousvalid only in case of discontinuous
flux (current) flow, it means flux (current) flow, it means ’ ’ << T - T -
At the point of At the point of ’ - I’ - IDD((’) = 0, hence:’) = 0, hence:
0
ppmax
0
2p
pmax
0
Dmax
S
0Dmax
nU
LI
Un
LnI
U
LI'
'LU
I0
S
(3)(3)
(4)(4)
From equation (4) :From equation (4) : '0
U
IIDD IIDmaxDmax
’ ’ TT
U0(R0)U’0(R’0 < R0)
II0kr0kr
==0,0,55
> 0,5> 0,5
II00
< 0,5< 0,5
1nU
U IN0
2T
RLIU 0ppmax0
0
2
2
0 2LfI
n
U
U
IN
Compare to flyback Compare to flyback regulator regulator
U0
for R0 < R0cr (I0 > I0cr) the flux in the core does not decay to 0 – so called „continuous flux flow” starts
IIDD
IITT
TT
IITmaxTmax
IIDmaxDmax
IIDminDmin
IDmax = nITmax
IDmin = nITmin
1nU
U InI :condition the from IN0DT
Real diagrams of flyback convertersReal diagrams of flyback converters
ZZp ZZS
ZZa
TT
DD
CC RR0 U0
UIN
CIN
DDd
ZZp=Za
CCss
RRssDDss
snubbar circuit for dumping snubbar circuit for dumping overvoltage spikes and reducing overvoltage spikes and reducing transistor power lossestransistor power losses
recovery of energy stored in the leakage inductancerecovery of energy stored in the leakage inductance
Advantages:Advantages:
Energy stored in leakage inductace is recovered, transitor voltage does not exceed 2UEnergy stored in leakage inductace is recovered, transitor voltage does not exceed 2U ININ
Disadvatages:Disadvatages:
Complicated and expensive transformerComplicated and expensive transformer
ZZp ZZS
TT
DD
CC RR0 U0
UIN
CIN
CsRs
Up
UT=Up+UIN
Disadvatages:Disadvatages:
Energy stored in the leakage inductance is dissipated in resistor Rs, lower efficiency, Energy stored in the leakage inductance is dissipated in resistor Rs, lower efficiency, necessity of power resistor utilisation, component heating, possibility of transitor necessity of power resistor utilisation, component heating, possibility of transitor voltage higher than 2Uvoltage higher than 2UININ
Advantages:Advantages:
Cheaper transformer, lack of extra overvoltage spikes due to residual leakage Cheaper transformer, lack of extra overvoltage spikes due to residual leakage inductanceinductance
This topology often used in low power converters up to 100WThis topology often used in low power converters up to 100W
2T
RLIpU T
R
U
2
ILs
pmaxs
2p
2pmax LL
LLLL
Leakage inductance measurement methodLeakage inductance measurement methodLLLLLLLL
Multi - output covertersMulti - output coverters
ZZp
ZZS1
TT
DD1
CC11RR01 U01
UIN
CIN
IID1D1 II0101
ZZS2
DD2
CC22RR02 U02
IID2D2 II0202
US1
US2
Flyback topologyFlyback topology
In II cycle In II cycle U01 = US1
U02 = US2 S2
S1
S2
S1
02
01
z
z
U
U
U
U
In this topology output voltages are dependent only on the secondary numbers of turns. In case of perfect magnetic coupling only one output voltage may be regulated to obtain the regulation of other outputs.
Valid for discontinuous as well as continuous current flow
One of the cheapest and simple solution delivering several regulated output voltages.
Feedback Feedback looploop
ZZp
ZZS1
ZZa
TT
DD2
DD1 LL11
CC RR01 U01
UIN
CIN
DDa
ZZS2DD4
DD3 LL22
CC RR02 U02
Forward converterForward converter
S2
p2
S1
p1 z
z nand
z
z n
202
101
n
UU
n
UU
IN
IN
12S2
S1
1
2
02
01 nz
z
n
n
U
U
This relation only valid in case of cotinuous magnetic flux (current) flow in L1 & L2
ZZp
ZZS1
ZZa
TT
DD2
DD1 LL11
C1C1 RR01 U01
UIN
CIN
DDd
ZZS2 DD4
DD3 LL22
C2C2 RR02 U02
Coupled output inductorsCoupled output inductors
LL11
U01
U02
1n
U IN
2n
U IN
'L1
U
'L2
ULL22
Equivalent output circuit valid for cycle I :Equivalent output circuit valid for cycle I :
1n
U IN
2n
U IN
1n
U
n
U
n
UU
n
UU
11101
1L1
ININININ'
1n
U
n
U
n
UU
n
UU
22202
2L2
ININININ'S2
S1
1
2
z
z
n
n
L2U
L1U
'
'
Equivalent output circuit valid for cycle II:Equivalent output circuit valid for cycle II:
LL11
U01
U02
"L1
U
"L2
ULL22
"L1
U
"L2
US2
S1
1
2
2
1
02
01
z
z
n
n
n
U
n
U
U
U
L2U
L1U
IN
IN
'
'
To achieve proper relation between output voltages the following condition To achieve proper relation between output voltages the following condition must be satisfied :must be satisfied :
S2
S1
z
z
L2U
L1U
L2U
L1U
"
"
'
'
L2
L1
S2
S1
z
z
z
z
In real circuit:
-diode voltage drop and nonlinear diode characteristics have significant influence on output voltages
-influece of winding resistances
-significant influence of leakage (poor winding coupling)
Detailed relations of turns number for particular windings are usually set by the way of experiment in practice – equations presented above give only the rough approximation.
ZZp ZZw
ZZd
TT
DD1
DD2
LL
CC RR0 U0
UIN
CIN
DDa
ZZp=Za
DD2
CC22 RR2 U2
LLn
U IN
CC22 RR2 U2
LL22
LL22
LL
CC22 RR2
LL22
U2
U0U0
zz22
zzLL0
L
Uz
zU 2
2
The other way of obtaining auxilliary regulated output voltages with low load The other way of obtaining auxilliary regulated output voltages with low load requirements :requirements :