Buck topology Half Bridge HB

V in
T
S 1
S 2
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 1]
Half Bridge, Full Bridge, Push-Pull, Cuk,
SEPIC
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 2]
S
V x
D
L
Buck topology
C
V o
R
V X
ton TS Buck derived topologies
Forward - one switch
Half Bridge HB - two switches
Full Bridge FB - four switches
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 3]
T
V 1
n V 2
V x
L
V C
2
V C
2
Half Bridge HB
C R
V o
S 1
S 2
V 1
V 2
V X
t on
HB Characteristics:
Frequency at output twice fs Output section: Buck
t on
t
t
t
t
t
t

V C
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 4]
S 1
S 2
C T
1
Full Bridge FB
S 3
S 4
S 1
S 2
S 3
S 4
T
n V 2
V x
L
C R
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 5]
T S
Reset of Forward, HB, FB
Forward - auxiliary winding
HB,FB - Natural
Example HB
V C
S 1
S 2
C 1 , C 2 capacitor divider
T
V 1
T
V1
n V 2
t on
V x
TS 2
VC 2
L
t
t
t
t
t on
TS 2
V o
C R
VC −
2
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 6]
C 1
C 2
Push-Pull
t
V o

Prof. S. Ben-Yaakov , Dc-DC Converters [7- 7]
I L ripple for same L
Forward:
∆I
HB, FB, PP:
2
Forward, HB, FB, PP
∆I
FORWARD
Switch Utilization
Important consideration: V s (off), I s (on)
I S
V S
Assumption:
Same input and output power
Same input voltage
t on
t off
I FW
⎡ Don
⎤
VC
⎢1+
⎥
⎣ Doff
⎦
t
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 8]
Waveforms
I S
V S
I S
V S
t on
t on
t off
t off
VC
V C
t
t
t
I HB =2I FW
I FB =I FW
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 9]
Stresses
IS V
FW 1 1+ Don
Doff
HB 2 1
PP 1 2
FB 1 1
Power conversion capability: FW

Prof. S. Ben-Yaakov , Dc-DC Converters [7- 10]
Topology selection
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 11]
V in
V in
V = V
V
1
2
L 1
c1
L 1
V 2
o
V = V
in
= V − V
in
o
C 1
VC1 S
Cuk Converter
L 2
D C
V 2
1
V out
ON OFF
L 2
C
C2 1
V out
R
R
V in
L 1
Vo
= −Vc
1 ⋅ D on (buck)
Vo
= −(
Vin
− Vo
) ⋅ D on
Vo
D on = −
Vin
D off
Voltage
C 1
of C 1 ≈ constant
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 12]
V in
L 1
V 2
Cuk with isolation
S
C 1a
1:n
Any polarity
C 1b
D
Any voltage ratio
Vo
D
=
±
V D
in
on
off
n
L 2
C 2
L 2
V out
C 2
R
V out
R

V in
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 13]
Cuk advnatages and disadvantages
Advantages
Continuos input and output currents
Single switch
Step-up and step-down
Disadvantages
Two inductors
Extra capacitor (of high rms current)
Difficult to stabilize
V V +
High voltage on switch in out
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 14]
L 1
S
V in
C 1
VL1
= 0
VL2
= 0
V x
VC1
= Vin
SEPIC Converter
L 2
L 1
C 2
S
R
o
in
C 1
V x
off
V in
L 2
Vx
= Vo
⋅D
V Don
=
V D
D
off
C 2
L 1
in
S
R
− V ⋅D
C 1
on
V out
ON OFF
= 0
V x D
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 15]
Auxiliary output
L 2
C 2
R

Prof. S. Ben-Yaakov , Dc-DC Converters [7- 16]
Topologies
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 17]
Topologies
Prof. S. Ben-Yaakov , Dc-DC Converters [7- 18]
HB waveforms

Prof. S. Ben-Yaakov , Dc-DC Converters [7- 19]
VOLTAGE REGULATION MODULE (VRM)
Synchronous rectifier