llc resonant half bridge converter design consideration

1

www.fairchildsemi.com

LLC Resonant Half Bridge Converter

Design Consideration

Marco Farneti

Field Application Engineer

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Agenda

1. Introduction

1. What is soft switching ?2. Soft Switching Operation

2. Resonant Converter Overview

1. Limitation of conventional resonant converter2. LLC Resonant Converter Overview

3. Integrated Transformer

3. LLC Resonant Converter Operation Mode

4. FSFR series Half-Bridge Resonant Converter and design Application1. Features of FSFR series

2. Application circuit for FSFR series

3. 3KW PSU Application - Block Diagram

4. 350W PSU Application - Block Diagram

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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

Capacitive loss Reverse recovery lossOverlap of voltage and current

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1.1 What is soft switching ?

Hard switching Overlap of voltage and current

Capacitive loss

Reverse recovery loss

Zero-voltage-switching (ZVS)

Turn on while switch voltage (Vds) is

zero by flowing current through the

anti parallel diode

Id

Vds

v, i

Psw

t on t off

t

t

on off

Vds

id

Vg

t

t

t

ids

Vg

V ds

I

VTurn-off

Turn-on

Hard-Switching mode

Soft-switching mode

ZVS

ZCS

[ The ideal zero-voltage soft switching ]

[ Switch voltage, current and power loss under hard switching ]

[ Switching loss of a switch during switching interval ]

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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

Q2

Q1

Resonant

Circuit

VDS

IDS

6


+

VO

-

Ro

Q1

Q2

n:1I

p

Lr

Lm

Cr

Ids2

Vd

Vin

resonant network

Series Resonant (SR) converter

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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7


+

VO

-

Ro

Q1

Q2

n:1I

p

Llkp

Cr

Ids2

Vd

Vin

resonant network

Parallel Resonant (PR) converter

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.

v IN

Q1

Q2

D1

D2

Vout+

-RLOADCr Lr

Co

Np:Ns

I ds1

Ids2

ID

Ir

+

-

+

-

Vds1

Vds2

Iout+-

v IN

Q1

Q2

D1

D2

Vout+

-RLOADCr Lr

Co

Np:Ns

I ds1

Ids2

ID

Ir

+

-

+

-

Vds1

Vds2

Iout+-

Cr

Half-bridge series resonant (SR) converter Half-bridge parallel resonant (PR) converter

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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

+

VO

-

Ro

Q1

Q2

n:1I

p

Lr

Lm

Cr

Ids2

Vd

Im

ID

Vin

resonant network

Io

+

VO

-

Ro

Q1

Q2

n:1I

p

Lr

Lm

Cr

Ids2

Vd

Vin

resonant network

LC Series resonant converter LLC resonant converter

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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

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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

LLC Resonant converter

v IN

Q1

Q2

D1

D2

Vout+

-RLOADCr Lr

Co

Lm

Np:Ns

I ds1

Ids2

ID

Im

Ir

+

-

+

-

Vds1

Vds2

Iout+- Half-bridge LLC resonant converter

//m ac acj L R R

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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

+

VO

-

Ro

Q1

Q2

n:1

Lr

Lm

Cr

Ids2

Vd

ID

Vin

Io

+

VO

-

Ro

Q1

Q2

n:1I

p

Llkp

Lm

Cr

Ids2

Vd

Llks

Im

ID

Vin

Integrated transformer

Io

7

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3. LLC Resonant Converter Operation mode

Below resonance (fs<fo)

Larger circulating current

Soft commutation of

rectifier diode

Above resonance (fs>fo) Smaller circulating current

Hard commutation of rectifier diode

Ip

Im

IO

ID

(I) fs < f

o Ip

ID I

O

Im

(II) fs > f

o

fo

fs

Gain (M)Below resonance

(fs<f

o)

above resonance

(fs>f

o)

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1) T1) T00~T~T11

3.1 Operation mode

LLC resonant HB converter

IN

Q1

Q2

D1

D2

Vout

+

-RLOADCr Lr

Co

Lm

Np:Ns

I ds1

Ids2

Im

Ir

+

-

+

-

Vds1

Vds2

- + ID

-+

t

t

t

t

t

t

t

t

t

VIN

On

Dead time

T0 T1 T2 3T 4T

C rmaxV

VC rmin

VCR

Vgs1

Vgs2

Vds1

Vds2

Ids1

Ir, Im

VCr

Iout

Ir

Im

IL rpeak

Off

VCOSSQ1

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

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22) T) T11~T~T22

3.2 Operation mode


vIN

Q1

Q2

D1

D2

Vout

+

-RLOADCr Lr

Co

Lm

Np:Ns

I ds1

Ids2

Im

Ir

+

-

+

-

Vds1

Vds2

- + ID

-+

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

t

t

t

t

t

t

t

VIN

T0 T1 T2 3T 4T

Vgs1

Vgs2

Vds1

Vds2

Ids1

V

Iout

Dead time

Ir, Im

C rmaxV

VC rmin

VC r

Cr

On Off

t

IL rpeakIr

Im

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33) T) T22~T~T33

3.3 Operation mode


vIN

Q1

Q2

D1

D2

Vout

+

-RLOADCr Lr

Co

Lm

Np:Ns

I ds1

Ids2

Im

Ir

+

-

+

-

Vds1

Vds2

- + ID

-+

Q1 is ON, Q2 is OFF

D1 and D2 are OFF; V(D1)=V(D2)=0

; transformer’s secondary is open

Ir=Im

t

t

t

t

t

t

t

t

t

VIN

Dead time

T0 T1 T2 T3T 4 T6T 5

C rmaxV

VC rmin

IL rpeak

VCR

Vgs1

Vgs2

Vds1

Vds2

Ids1

Ir, Im

V Cr

Iout

Ir

Im

On Off

VCOSSQ1

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33) T) T33~T~T44

3.4 Operation mode


vIN

Q1

Q2

D1

D2

Vout

+

-RLOADCr Lr

Co

Lm

Np:Ns

I ds1

Ids2

Im

Ir

+

-

+

-

Vds1

Vds2

- + ID

-+

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

t

t

t

t

t

t

t

t

VIN

Dead time

T0 T1 T2 T3T 4 T6T 5

C rmaxV

VC rmin

IL rpeak

VCR

Vgs1

Vgs2

Vds1

Vds2

Ids1

Ir, Im

V Cr

Iout

Ir

Im

On Off

VCOSSQ1

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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

HV IC

2 MOSFET

Advantage through system integration

• High reliability & productivity

• BOM cost reduction

• Easy design

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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)

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4.2 Application circuit for FSFR series

Control

IC

C105

22uF/

50V

Vcc

VDLLVcc

RT

CON

CS

SG PG

VCTR

HVcc

Ns

VoNp Ns

C101

220uF/

450V

R104

7.2k

R105

7.2kC107

6.8uF

R107

3.9k

JP1

10

R106

270

D101

1N4137

C102

22nF/

630V

D211

FYP2010DN

D212

FYP2010DN

C106

150nF

U3

KA431 C203

47nF

R203

33k

R205

7k

R204

62k

R202

1k

R201

10k

C201

2200uF

35V

C202

2200uF

35V

R101

0.2Ω

R102

1kΩ

C102

100pF

C108

12nF

R206

2k

C204

12nF

Vin=400Vdc

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

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4.3 3KW PSU Application - Block Diagram

P F CRectifier

2SK3235(HITACHI)*6EAKSU20B60(Nihon Inter)*2EA

D25XB60 (600V 25A)SHINDENGEN*2EA

PFC IC

TK83854(TOKO)PFC controller

FQAF24N50(FAIRCHILD)*6EA

Output

42V_66A

Input

100-240Vac

switching regulator

CXA8038A(SONY)Resonant mode

DC-DC Converter

KCF25A20(Nihon Inter)*6EA

2SK3313(TOSHIBA)*2EA

switching regulator

CXA8038A(SONY)Resonant mode

DC-DC Converter

FCH30A06(Nihon Inter)*2EA

Output

12V_12A

KCQ60A06(Nihon Inter)*3EA

FCH30A03L(Nihon Inter)*1EA

Synchronous Buck Converter

Output

3.3V_25A

2SK3573(NEC)*1EASI4894(VISHAY)*10EA

Controller

PU5103(TI)Synchronous DC/DC

LLC Resonant HBLLC Resonant HB


CCM PFCCCM PFC

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4.4 350W PSU Application - Block Diagram

Rectifier

Input

100-240Vac

FQPF13N50CF(FSC)*2EA

switching regulator

CXA8038A(SONY)

Resonant mode

DC-DC Converter

IPP06CN10N(Infineon)*2EA

Output

12V_32A

P F C

PFC IC

UC3854DW

SPA21N60C3_Infineon*1EA

STTH15R 06FP_ST*1EA

Synchronous Rectification

MIP2G4(Panasonic)*1EA

Flyback

converter

5V 3A STB

FCH10A15(Nihon Inter)*1EA

DCM PFCDCM PFC


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llc resonant half bridge converter design consideration

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