LLC Resonant Half Bridge Converter
Design Consideration
Marco Farneti
Field Application Engineer
www.fairchildsemi.com
Agenda
1.
Introduction
1. What is soft switching ?
2.
2.
Soft Switching Operation
Resonant Converter Overview
1. Limitation of conventional resonant converter
2.
3.
LLC Resonant Converter Overview
Integrated Transformer
3.
LLC Resonant Converter Operation Mode
4.
FSFR series Half-Bridge Resonant Converter and design Application
1.
2.
3.
4.
Features of FSFR series
Application circuit for FSFR series
3KW PSU Application - Block Diagram
350W PSU Application - Block Diagram
2
1
1. Introduction
 Growing demand for higher power
density and low profile in power
converter has forced to increase
switching frequency
 However, Switching Loss has been
an obstacle to high frequency
operation
Overlap of voltage and current
Reverse recovery loss
Capacitive loss
3
1.1 What is soft switching ?
v, i
Hard switching



Overlap of voltage and current
Capacitive loss
Reverse recovery loss
Vds
Id
i ds
t
Psw
Zero-voltage-switching (ZVS)
Turn on while switch voltage (Vds) is
zero by flowing current through the
anti parallel diode
t on
V ds
t
t off
[ Switch voltage, current and power loss under hard switching ]
Hard-Switching mode
I
Vg
Vg
Turn-on
t
id
t
Vds
t
on
off
[ The ideal zero-voltage soft switching ]
ZCS
Soft-switching mode
ZVS
Turn-off
V
[ Switching loss of a switch during switching interval ]
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2
1.2 Soft Switching Operation

Resonant converter: processes power in a sinusoidal manner and
the switching devices are softly commutated
 Voltage across the switch drops to zero before switch turns on (ZVS)
• Remove overlap area between V and I when turning on
• Capacitive loss is eliminated
 Series resonant converter / Parallel resonant converter
Q1
Resonant
Circuit
IDS
Q2
VDS
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2. Resonant Converter Overview
Series Resonant (SR) converter
resonant network
Q1
Ip
Vin
Vd
Q2
n:1
Ro
Lr
Lm
Ids2
+
VO
-
Cr
The resonant inductor (Lr) and resonant capacitor (Cr) are in series
The resonant capacitor is in series with the load
The resonant tank and the load act as a voltage divider DC gain is always
lower than 1 (maximum gain happens at the resonant frequency)
The impedance of resonant tank can be changed by varying the frequency of
driving voltage (Vd)
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3
2. Resonant Converter Overview
Parallel Resonant (PR) converter
resonant network
Q1
Ip
Vin
Vd
n:1
Ro
Llkp
Q2
+
VO
Cr
-
Ids2
The resonant inductor (Lr) and resonant capacitor (Cr) are in series
The resonant capacitor is in parallel with the load
The impedance of resonant tank can be changed by varying the
frequency of driving voltage (Vd)
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2.1 Limitation of SRC and PRC resonant
Limitation of the conventional SRC(Series Resonant Converter)
Can optimize performance at one operating point, but not with wide range of input voltage
and load variations (too wide frequency range)
 Difficult to regulate the output at light or no load condition

Limitation of the conventional PRC(Parallel Resonant Converter)
Large amount of circulating current because the load is connected in parallel with the
resonant network,
 Difficult to apply in high power applications.

I ds1
I ds1
Vds1 +
Vds1 +
Q1
Np:Ns
-
v IN
+
Vds2 +
D1
Ir
Ids2
Cr
Q1
Co
Lr
Np:Ns
ID
+
-
Iout
Vout
R
LOAD
Q2
v IN
+
Vds2 +
Q2
-
D1
Ir
Ids2
Cr
ID
Co
Lr
+
-
Iout
Vout
R
LOAD
Cr
-
D2
Half-bridge series resonant (SR) converter
D2
Half-bridge parallel resonant (PR) converter
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4
2.2 LLC Resonant Converter Overview
LLC resonant converter
 Topology looks almost same as the conventional LC series
resonant converter
 Magnetizing inductance (Lm) of the transformer is relatively small
and involved in the resonance operation
 Voltage gain is different from that of LC series resonant converter
LC Series resonant converter
resonant network
Q1
Ip
Vin
LLC resonant converter
Vd
Q2
Ro
Lr
Ids2
+
VO
Lm
resonant network
Q1
n:1
Cr
Ip
Vin
Vd
Q2
n:1
Io
ID
Ro
Lr
VO
Im
Lm
Ids2
+
Cr
9
2.2 LLC Resonant Converter Overview
 Features of LLC resonant converter
- Reduced switching loss through ZVS: Improved efficiency
- Narrow frequency variation range over wide load range
- Zero voltage switching even at no load condition
- Typically, integrated transformer is used instead of discrete magnetic
components
10
5
2.2 LLC Resonant Converter Overview
LLC Resonant converter
Advantages

 Reduced switching loss through ZVS  Improved efficiency and EMI
 Reduced magnetic components size by high frequency operation
 Narrow frequency variation range over wide load range
Drawbacks

 Larger circulating current compared to LC resonant converter due to the relatively
small magnetizing inductance
 Difficult to optimize transformer design
jLm // Rac  Rac
I ds1
Vds1 +
Q1
Np:Ns
-
v IN
+
Vds2 +
D1
Ir
Ids2
ID
Co
Lr
Cr
Im
Q2
+
-
Iout
Vout
R
Half-bridge LLC resonant converter
LOAD
Lm
D2
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2.3 Integrated Transformer
 Integrated transformer in LLC resonant converter
 Two magnetic components are implemented with a single core (use
the primary side leakage inductance as a resonant inductor)
 One magnetic components (Lr) can be saved
 Leakage inductance not only exists in the primary side but also in
the secondary side
 Need to consider the leakage inductance in the secondary side
Q1
Vin
Integrated transformer
Q1
n:1
Vd
Q2
Ids2
Io
ID
Ro
Lr
+
VO
Lm
Ip
Vin
Vd
Q2
Cr
Llks
Im
Lm
Ids2
Io
ID
n:1
Llkp
Ro
+
VO
-
Cr
12
6
3. LLC Resonant Converter Operation mode
Gain (M)
Below resonance
(fs<fo)
above resonance
(fs>fo)
Above resonance (fs>fo)
Below resonance (fs<fo)
fo
Ip
(I) fs < fo
Im
Smaller circulating current
Hard commutation of rectifier
diode


Larger circulating current
Soft commutation of
rectifier diode


Ip
ID
fs
(II) fs > fo
Im
ID
IO
IO
13
3.1 Operation mode
LLC resonant HB converter
1) T0~T1
Vgs2
Q1
Np:Ns
- +
+
Vds2 +
Q2
t
Dead time
Vds1 +
IN
Off
On
Vgs1
I ds1
Ids2
Cr
t
D1
VIN
Ir
ID
Co
Lr
Im
+
-
Vds1
Vout
t
R LOAD
Vds2
t
Lm
-
Ids1
t
D2
VCOSS Q1
I L rpeak
Ir, Im
Q1 is ON, Q2 is OFF
D1 is ON, D2 is OFF; V(D2) = -2·Vout
Ir flows through Q1’s body diode  ZVS Condition
Lm is charged with constant voltage
t
Ir
Im
t
VC rmax
VCR
V Cr
VC rmin
Iout
T0 T1
T2T3 T4
t
t
14
7
3.2 Operation mode
LLC resonant HB converter
2) T1~T2
Vgs2
Q1
Np:Ns
- +
+
Vds2 +
t
Dead time
Vds1 +
v IN
Off
On
Vgs1
I ds1
Ids2
Cr
VIN
ID
Co
Lr
Im
Q2
t
D1
Ir
+
-
Vds1
Vout
t
R LOAD
Vds2
t
Lm
-
Ids1
t
D2
I L rpeak
Q1 is ON, Q2 is OFF
D1 is ON, D2 is OFF; V(D2) = -2·Vout
Lm is dynamically shorted: V(Lm) = Ns/Np·Vout.
Cr resonates with Lm
Ir flows through Q1’s RDS(on) from Vin to Gound
Energy is taken from Vin and goes to Vout
t
Ir
Ir, Im
Im
t
VC rmax
VC r
V Cr
t
VC rmin
Iout
T0 T1
T2T3T4
t
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3.3 Operation mode
LLC resonant HB converter
3) T2~T3
Vgs2
Q1
Np:Ns
- +
+
Vds2 +
Q2
t
Dead time
Vds1 +
v IN
Off
On
Vgs1
I ds1
Ids2
Cr
VIN
ID
Co
Lr
Im
t
D1
Ir
+
-
Vds1
Vout
t
R LOAD
Vds2
t
Lm
-
Ids1
t
D2
VCOSS Q1
I L rpeak
Ir, Im
Q1 is ON, Q2 is OFF
D1 and D2 are OFF; V(D1)=V(D2)=0
; transformer’s secondary is open
Ir=Im
t
Ir
Im
t
VC rmax
VCR
V Cr
t
VC rmin
Iout
T0 T1
T2T3T4
T6 T5
t
16
8
3.4 Operation mode
LLC resonant HB converter
3) T3~T4
Vgs2
Q1
Np:Ns
- +
+
Vds2 +
Q2
t
Dead time
Vds1 +
v IN
Off
On
Vgs1
I ds1
Ids2
Cr
VIN
ID
Co
Lr
Im
t
D1
Ir
+
-
Vds1
Vout
t
R LOAD
Vds2
t
Lm
Ids1
-
t
D2
VCOSS Q1
I L rpeak
Ir, Im
Q1 and Q2 are OFF (dead-time)
D1 and D2 are OFF; V(D1)=V(D2)=0
; transformer’s secondary is open
I(Lr+Lm) charges Coss of Q1 and discharges Coss of Q2,
until V(Coss of Q2)=0
; Q2’s body diode starts conducting
Output energy comes from Co
Phase ends when Q2 is switched on
t
Ir
Im
t
VC rmax
VCR
V Cr
t
VC rmin
Iout
T0 T1
T2T3T4
T6 T5
t
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4. FSFR series HB Resonant Converter
 PWM / PFM Controller + High side Drive IC + 2 MOSFET
in 9-SIP PKG
 Universal controller : can be applied various topology
 High-side drive IC : has immunity against switching noise
 MOSFET with fast recovery body diode trr = 120ns
PWM IC
Advantage through system integration
• High reliability & productivity
• BOM cost reduction
• Easy design
2 MOSFET
HV IC
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9
4.1 Features of FSFR series
Variable frequency control with 50% duty cycle for half-bridge resonant converter topology
High efficiency through zero voltage switching (ZVS) : typ. Eff=93~94% for Vo=24V
Internal MOSFETs with Fast Recovery Type Body Diode (trr=120ns)
Internally optimized dead time (fixed. 350ns)
Up to 300kHz operating frequency
Pulse skipping for Frequency limit (programmable) at light load condition
Simple remote ON/OFF control
Various Protection functions: Over Voltage Protection (OVP), Over Current Protection
(OCP), Abnormal Over Current Protection (AOCP), Internal Thermal Shutdown (TSD)
19
4.2 Application circuit for FSFR series
D211
FYP2010DN
C102
22nF/
630V
Vcc
JP1
10
R106
270
LVcc
C105
22uF/
50V
Vin=400Vdc
D101
1N4137
Np
R105
7.2k
C108
12nF
Ns
R102
1kΩ
R201
10k
C106
150nF
CON
Control
IC
VCTR
R202
1k
C102
100pF
SG
PG
R101
0.2Ω

C204
12nF
R204
62k
D212
FYP2010DN
R206
2k
U3
KA431
CS
C101
220uF/
450V
Vo
HVcc
C107
6.8uF
R107
3.9k
C201
2200uF
35V
Ns
VDL
RT
R104
7.2k
C202
2200uF
35V
C203
47nF
R203
33k
R205
7k
LLC resonant converter for LCD TV
 Vin=350~400V, Vo=25V, Io=8A (200W)
 Eff=94% at full load
 No heat sink is required up to 200W
20
10
4.3 3KW PSU Application - Block Diagram
LLC Resonant HB
DC-DC Converter
CCM PFC
Output
42V_66A
PFC
Rectifier
KCQ60A06(Nihon Inter)*3EA
Input
100-240Vac
2SK3235(HITACHI)*6EA
KSU20B60(Nihon Inter)*2EA
PFC IC
TK83854(TOKO)
PFC controller
D25XB60 (600V 25A)
SHINDENGEN*2EA
FQAF24N50(FAIRCHILD)*6EAKCF25A20(Nihon Inter)*6EA
switching regulator
LLC Resonant HB
CXA8038A(SONY)
Resonant mode
Synchronous Buck Converter
Output
12V_12A
DC-DC Converter
SI4894(VISHAY)*10EA2SK3573(NEC)*1EA
Output
3.3V_25A
FCH30A03L(Nihon Inter)*1EA
2SK3313(TOSHIBA)*2EA FCH30A06(Nihon Inter)*2EA
switching regulator
Controller
CXA8038A(SONY)
Resonant mode
PU5103(TI)
Synchronous DC/DC
21
4.4 350W PSU Application - Block Diagram
LLC Resonant HB
SPA21N60C3_Infineon*1EA
STTH15R06FP_ST*1EA
Rectifier
DC-DC Converter
P F PFC
C
DCM
SynchronousRectification
Input
100-240Vac
Output
12V_32A
FQPF13N50CF(FSC)*2EA
IPP06CN10N(Infineon)*2EA
UC3854DW
switching regulator
PFC IC
Flyback
converter
CXA8038A(SONY)
Resonantmode
5V 3A STB
MIP2G4(Panasonic)*1EA
FCH10A15(NihonInter)*1EA
22
11
Thank you
www.fairchildsemi.com
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