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DIEUPM
DC/DC Power Converters
DC/DC switched modeconverters
Topologies with isolation
DC/DC switched modeDC/DC switched modeconvertersconverters
Topologies with isolationTopologies with isolation
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DIEUPM
DC/DC Power Converters
Topologies with transformer
Energy: transferred and stored
Stored energy: magnetizing (Lm) and Leakage (Llk)
Lm is common energy. Located in any winding
Simplified modelSimplified model
d
dt
u
n
u
n
u
n
p
p
φ = = = =
1
1
2
2
....
n i n i1 1 2 2⋅ = ⋅
L
Relmag, i =
ni2
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DIEUPM
DC/DC Power Converters
Square wave converterSquare wave converter inin steady statesteady state
Steady state circuit
n1 : n2
v1 v2
+
-
+
-
vi
= ni
· dΦ/dt
Φ= ΦB - Φ A = (v i/n i)·dt∫
B
A
Faraday´s law:
Steady state:
( Φ)cycle
= 0
Topologies with transformer
V1,avg = V2,avg = 0
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DIEUPM
DC/DC Power Converters
Flyback Flyback (I)(I)
Straight forwardStraight forward
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DIEUPM
DC/DC Power Converters
Flyback Flyback (II)(II)
Transformer behavesTransformer behaves asas twotwo
coupled inductorscoupled inductors
Energy storage
Energy storage
Normally, there is a gapNormally, there is a gap
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DIEUPM
DC/DC Power Converters
Flyback Flyback (III)(III)
VO
+
-
vS
+
-
Vg
+
-v
D
n1 n2
d·T·Vg/n1 - (1-d)·T·VO/n2 = 0
VO = Vg·(n2/n1)·d/(1-d)
vD max = Vg·n2/n1 + VO= Vg·(n2/n1)·/(1-d)
vS max = Vg+VO·n1/n2 = Vg/(1-d)
Voltage stress
Volt. balance
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DIEUPM
DC/DC Power Converters
Flyback vs Buck Flyback vs Buck --BoostBoost
Buck-Boost
50V
2A
100V
1A (avg)
S
D
L
100W
vS max = vD max = 150V
iS=1A iD=2A iL=3A
VAS = 150VA VAD = 200VA
Equal stressEqual stress
vS max = vD max = 150V
iS=1A iD=2A
VAS = 150VA VAD = 200VA
50V
2A
100V
1A (avg)
S
D
100WFlyback
1:1
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DIEUPM
DC/DC Power Converters
From Buck to Forward
Ue
Us
••
PROBLEM:PROBLEM: transformer demagnetizationtransformer demagnetization
Magnetizing current needs to flow through any winding
Imag
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DIEUPM
DC/DC Power Converters
This is the solutionThis is the solution
Lm
Demagnetizing
Voltage
From Buck to Forward
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DIEUPM
DC/DC Power Converters
Forward converterForward converter (I)(I)
Vg n2
n1
Demagnetization based oninput voltage
V1 = V2 = Vg
Considering:
d’ = d·n2/n1 d’ < 1 - d
then:
d < n1/(n1 + n2) dmax = n1/(n1 + n2)
V1
V2
n2
n1
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DIEUPM
DC/DC Power Converters
Forward converterForward converter (II)(II)
VO
n2:n3
n1
+
-vD2
vS
+
-
vD1
+
-Vg
vS max = Vg+Vg·n1/n2 = Vg/(1-dmax)
vD1 max = Vg·n3/n1
vD2 max = Vg·n3/n2
dmax = n1/(n1 + n2)
Vg·n3/n1 VO
+
-
ON time d·T
VO = d·Vg·n3/n1(in CCM)
VO-
+
OFF time (1-d)·T
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DIEUPM
DC/DC Power Converters
Forward converterForward converter (III)(III)
iD2
VOVg n2:n3
n1
iS
iL
iD1
iD3iO
iD2·n3/n1
T
d·T
t
Vgs
t
iLiO
d’·T
iD3
iD2
iD1
iS
t
t
t
t
iD2 = IO·d iD1 = IO·(1-d)
im = Vg·T·d2/(2·Lm) (from primary)
iS = IO·d·n3/n1 + im iD3 = im
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DIEUPM
DC/DC Power Converters
Buck Buck vsvs ForwardForward
Higher Higher VVSS maxmax inin ForwardForward
Forward
50V
2A
100V
1A (avg)
S
D1
L
100W1 : 1:1
D2D3
VAS = 200VA VAD = 100VA
iS=1A iD1= iD2=1A
vD1 max= vD2 max= 100V
vS max=200V iL=2A
Buck
50V
100V
2A1A (avg)
S D
L
100W
vS max=vD max=100V
iS
=1A iD
=1A iL
=2A
VAS=100VA VAD=100VA
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DIEUPM
DC/DC Power Converters
Reset windingReset winding (n2)(n2) designdesign
vD2
VO
n2:n3
n1
+ -
vS
+
-
vD1
+
-Vg
Φ
t
v i/n i
t+-
Vg/n1
Φ
max
Vg/n2
Φ
t
v i/n i
t+
-
Vg/n1
Φmax
Vg/n2Low Vg
Φ
t
v i/n i
t+ -
Vg/n1
Φmax
Vg/n’2
Lower stress High Vg
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DIEUPM
DC/DC Power Converters
Two switches
☺ Lower BVdss (Vg)
Two switches
☺ Lower BVdss (Vg)
Forward withForward with 22 switchesswitches
Φ
t
v i/n i
t+
-
Vg/n1
Φmax
Vg/n1dmax = 0.5
VO = d·Vg·n2/n1 (in CCM)
vS1 max = vS2 max = Vg
vD1 max = vD2 max = Vg
vD3 max = vD4 max = Vg·n2/n1
Vg
n1 : n2
S1D4
D3
D1
D2
S2
VO
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DIEUPM
DC/DC Power Converters
Boost with IsolationBoost with Isolation??
•Not possible using just a single switch
• Multiple switch Current fed converters
••Not possibleNot possible using just a single switch
• Multiple switch Current fed converters
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DIEUPM
DC/DC Power Converters
Classical invertersClassical inverters
VOVg
S2S1“Push-pull” VO
Vg
S2
S1
Half Bridge
S2
S1
Vg
S3
S4
VO
Full Bridge
Inverter structures
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DIEUPM
DC/DC Power Converters
DC/DCDC/DC ConvertersConverters based on invertersbased on inverters
“push-pull”
inverter Center tapped “push-pull”
CDR - “ push-pull”Single ended “ push-pull”
Inverter structures
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DIEUPM
DC/DC Power Converters
PushPush--pullpull (I)(I)
Forward Forward
“ push-pull”
B
B
H
B
B
H
Inverter structures
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DIEUPM
DC/DC Power Converters
S2 S1
n1 : n2
n1
n1
n2
n2
Vg
VO
L
•When S2 is ON:
Vg·n2/n1
LVO
• When S1 is ON:
Vg·n2/n1
LVO
When BOTH S1 & S2 are OFF ?
Inverter structures
PushPush--pullpull (II)(II)
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DIEUPM
DC/DC Power Converters
L
VO
iL
D1
D2
iL1
iL2
• Equivalent circuit when
both S1 & S2 are OFF:
•D1 & D2 conduct
Transformer voltage is
zero
• iL1 and iL1 must:
iL1 + iL2 = iLiL1 - iL2 = iLm (sec. trans.)
VOL
Inverter structures
PushPush--pullpull (III)(III)
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DIEUPM
DC/DC Power Converters
•
vD is as a Forward with double frequency and2·d VO = 2·d·Vg·n2/n1 (CCM)
• vsmax = 2·Vg vD1max = vD2max = 2·Vg·n2/n1
S2
n1
n1
n2
n2
Vg
VO
LvD
+
-
S1
+ -
vD1
+ -
vD2
vS1+-
+
-
vS2
D1
D2
t
vS2
t
t
Td·T
t
t
Vgs
t
vS1
vD1
vD2
vD
2·Vg
2·Vg
Vg·n2/n1
2·Vg·n2/n1
2·Vg·n2/n1
S1 S2
dmax = 0.5
Inverter structures
PushPush--pullpull (IV)(IV)
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DIEUPM
DC/DC Power Converters
S2 S1
n1 : n2
n1
n1
n2
n2
Vg
VO
L
iS1
iL
D1
D2
iD1
iD2
iS2
iO
Average currents:
iS1 = iS2 = iO·d·(n2/n1) iD1 = iD2 = iO/2
t
t
t
iL
Vgs
iS2
t
iD1
iS1
t
Td·T
t
iD2
S1 S2
dmax = 0.5
Inverter structures
PushPush--pullpull (V)(V)
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DIEUPM
DC/DC Power Converters
S2 S1
n1
n1Vg
VO
iS1
iS2
• Risk of saturation in “ Voltage Mode”
• “ Current mode” is preferred
B
B
H
Inverter structures
PushPush--pullpull (VI)(VI)
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DIEUPM
DC/DC Power Converters
• vD is as half than in Push-pull
VO = d·Vg·n2/n1 (in CCM)
• vsmax = Vg vD1max = vD2max = Vg·n2/n1
VO
S2
n1
n2
n2Vg
L
vD+
-
S1
+ -
vD1
+ -
vD2
vS1+-
+
-
vS2
D1
D2
Vg/2
Vg/2 t
vS2
t
t
Td·T
t
tVgs
t
vS1
vD1
vD2
vD
Vg
Vg
Vg·0.5·n2/n1
Vg·n2/n1
Vg·n2/n1
S1 S2
dmax = 0.5
Inverter structures
HalfHalf Bridge (I)Bridge (I)
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DIEUPM
DC/DC Power Converters
iD1 iL
S2
n1
n2
n2Vg
LiO
S1
iD2
iS1
iS2
D1
D2
VO
Vg/2
Vg/2
Average currents:
iS1 = iS2 = iO·d·(n2/n1) iD1 = iD2 = iO/2
t
t
t
iL
Vgs
iS2
t
iD1
iS1
t
Td·T
t
iD2
S1 S2
dmax = 0.5
Inverter structures
HalfHalf Bridge (II)Bridge (II)
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DIEUPM
DC/DC Power Converters
• Same vD as Push-pull
VO = 2·d·Vg·n2/n1 (in CCM)
• vsmax = Vg vD1max = vD2max = 2·Vg·n2/n1
VO
S3
n1
n2
n2Vg
L
vD+
-
S4
+ -
vD1
+ -
vD2
vS4
+
-
+
-
vS3
D1
D2
S1
S2
vS2, vS3
t
Vgs
t
vS1, vS4 Vg
Vg
t
t
t
Td·T
t
vD1
vD2
vD Vg·n2/n1
2·Vg·n2/n1
2·Vg·n2/n1
S1, S4 S2, S3
dmax = 0.5
Inverter structures
FullFull Bridge (I)Bridge (I)
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DIEUPM
DC/DC Power Converters
Average currents:
iS3 = iS4 = iO·d·(n2/n1) iD1 = iD2 = iO/2
iD1 iL iO
iD2
iS4
VO
S3
n1
n2
n2Vg
L
S4
D1
D2
S1
S2
iS3
t
t
t
iL
Vgs
iS2, iS3
t
iD1
iS1, iS4
t
Td·T
t
iD2
S2
, S3
S1, S
4
dmax = 0.5
Inverter structures
FullFull Bridge (II)Bridge (II)
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DIEUPM
DC/DC Power Converters
• Risk of saturation in “ Voltage Mode”
• Solution:• CS in series
• Use “ Current Mode”
S2
S1CS
Vg
VO
S3
S4
Inverter structures
FullFull Bridge (III)Bridge (III)
I t t t
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DIEUPM
DC/DC Power Converters
Vg
vS
iS
Vg
Vg +
-
+
-
+
-
vS
vS
iS
iS
PO
PO
PO
vSmax = 2·Vg iS = PO/(2·Vg)High MOSFET voltage stress
Good only for low Vg
vSmax = Vg iS = PO/VgHigh input current
Good for high Vg
vSmax = Vg iS = PO/(2·Vg)Low stresses
Good for high power
ComparisonComparison
Inverter structures
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DIEUPM
DC/DC Power Converters
DC/DC switched modeconverters
Current fed converters
DC/DC switched modeDC/DC switched modeconvertersconverters
Current fed convertersCurrent fed converters
C rrent fed con erters
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DIEUPM
DC/DC Power Converters
Current fed inverters andCurrent fed inverters and DC/DCDC/DC convertersconverters
“Push-pull”
inverter Full Bridge
inverter
DC/DC Current fed
“Push-pull”DC/DC Current fed
Full Bridge
Current fed converters
Current fed converters
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DIEUPM
DC/DC Power Converters
t
Vgs of S1
t
Vgs of S2
t
vS2
t
Td·T
t
tvS1
vD1 2·VO
2·VO·n1/n2
2·VO·n1/n2
VO
vD2 2·VOVO
Current fedCurrent fed “ “PushPush--pullpull” ” (I)(I)
Vg+-Vg
VO·n1/n2 VO·n1/n2
Vg+-
Both S1 &
S2 ONS1 OFF S2 OFF
n1
n1
n2
n2Vg
VO
S2S1
+ -
vD1
+
- vD2
vS2+
-
dmin = 0.5
Current fed converters
Current fed converters
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DIEUPM
DC/DC Power Converters
VoltVolt ..secondsecond balancebalance
VO = Vg·(n2/n1)/2(1-d)
(in CCM)(in CCM)
Vg
S1 & S2ON
+
-Vg
VO·n1/n2
S1 OFF
VO·n1/n2
Vg
+
-S2 OFF
Vg
S1 & S2ON
d·T (1-d)·T
t1 t1t2 t2
1
Current fed converters
Current fedCurrent fed “ “PushPush--pullpull” ” (II)(II)
Current fed converters
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DIEUPM
DC/DC Power Converters
iL
iO
n1
n1
n2
n2VgS2S1
iD1
iD2
iS2 dmin = 0.5
iS1
Td·T
t
iD1
t
iS2
t
t
iS1
iL
t
Vgs de S1
t
Vgs de S2
iD2iS1 = iS2 = iO·(n2/n1)/4(1-d)
iD1 = iD2 = iO/2
Current fed converters
Current fedCurrent fed “ “PushPush--pullpull” ” (III)(III)
Current fed converters
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DIEUPM
DC/DC Power Converters
S2S1
iLPossible problem: Provide a path
for inductor current when turningthe converter off (S1 and S2 are
OFF!!)
iL
Current fed converters
Current fedCurrent fed “ “PushPush--pullpull” ” (IV)(IV)
Current fed converters
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DIEUPM
DC/DC Power Converters
Return energy to input
Current fed converters
Current fedCurrent fed “ “PushPush--pullpull” ” (IV)(IV)
Return energy to
output
Current fed converters
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DIEUPM
DC/DC Power Converters
Vg VOn1 n2n2 n1
VO Vg
d 1-d
1-d d
Changes
VO = Vg·d
Vg VO
Buck VO = Vg/(1-d)
VgVO
Boost
Voltage fed “ Push-pull”
VO = 2·d·Vg·n2/n1
Vg
VOn1
n1
n2
n2
Current fed “ Push-pull”
VO = Vg·(n2/n1)/2(1-d)
Vg
VOn1
n1
n2
n2
Current fed converters
Current fed vs voltage fedCurrent fed vs voltage fed
Current fed converters
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DIEUPM
DC/DC Power Converters
Same as Push-pull except
voltage stress in the MOSFET
Same as Push-pull except
voltage stress in the MOSFET
Current fed converters
Current fedCurrent fed “ “FullFull BridgeBridge” ” (I)(I)
Return energy to input
Return energy to
output
Current fed converters
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DIEUPM
DC/DC Power Converters
Full wave rectifierFull wave rectifier
Current fed “ Push-pull”
Current fed “Full Bridge”
Current fed converters