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 :