phinguyenpresentation-ee136

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Presentation

Student: Phi Nguyen (3631)

Date: 12/06/2003

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TRANSFORMER DESIGN

FOR FORWARD CONVERTERAND HALF BRIDGE FORWARD

CONVERTER

Agenda

1) Introduction

2) Circuit Illumination of DC to DC

3) Steps for Transformer design4) Example for Transformer design

Forward Converter

Half Bridge Converter(optional)

5) Advantage6) Conclusion

7) Question

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Introduction

- Transformer has two basic functions: to

provide electrical isolation and step up or step

down time varying voltage and current.

DC-to-DC converter enables the transformer to be

small.

- It can provide multiple output voltage.

- Throughout the design transformer, the coresize, optimum induction is selected and the

primary turns, secondary turns are calculated.

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CIRCUIT ILUMINATION OF DC-TO-DC FORWARD AND

HALF BRIDGE CONVERTER

In general, the transformer for the half bridge converter follows the

same general principal used for the forward converter.

Buck dc-dc converter: Vo=VdD

Forward & Half bridge conv.: Vo= Vd1

2

N

ND

Figure 1 - Forward converter

N1 N3 N2LmVd

D1

D2

D3

C1 Vo

S1

L1

Figure 2 - Half bridge forward converter

S1

S2

Vd

C1

C2

N1

N2

N2'

D1

D2

C Vo

Lx

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THE STEPS FOR TRANSFORMER DESIGN

Step 1: Selecting core size.From the basic of transmitted power and

the manufactures recommendation.

(Figure 2.2.2)

Step 2: Selecting optimum induction.

Use manufactures published chart.(Figure 2.9.1)

Step 3: Calculate primary turns.

Step 4: Calculate secondary turns.

2

1

2

1

N

N

V

V=

Note: Maximum duty ratio:

Dmax= 0.5 (ton=toff).

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EXAMPLE FOR TRANFORMER DESIGN

* Forward converter:

P = 100W at fsw 30 kHz.Input: Vi = 90 130 V (nominal 110V) 50-60Hz.

Output Vo and Io :

5V at 10 A (50W)

+12V at 2A (24W)

-12V at 2A (24W)

Total = 98W

-Core size: Use figure 2.2.2

At 100W E 42-15.

Core parameters: area Ae=181 mm

2

-Optimum induction: Use figure 2.9.1

At 100W and f = 30kHz.

Bopt=150mT (for push pull).

. Bm=250mT (for forward conv.)

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-Calculate primary turns:

Tsw=swf

1= 33s ton =

2

Tsw= 16.5 s

-Calculate primary voltage (V1):

Use the approximate conversion factor:

V1 = Vi x (1.3) x (1.9)

V1 = 110 x (1.3) x (1.9) = 272V

Min. primary turns:

Nmin =)2(mmA.(T)B

).(t.(V)V

em

on1 s= 100 turns

At V1 min = 90V in dc primary voltage

V1min= 90 x (1.3) x (1.9) = 222 V

V/turn =min

min1

N

V=

100

222= 2.22 V/turn

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-Calculate secondary turns:

N2 D2 C Vo

Lx

V2

Figure 3 - Single output application

Vo = V2 x Dmax V2 =maxD

Vo= 10V.

Choose V2 = 12V (2V drop D1 and Lx)

N2min = 22.2

12

= 5.4 turns. Choose N2 = 5.5 turns.

2

2

1

min1

N

V

N

V=

N1=V1min2

2

V

N= 102 turns.

Similarly, we have:

V2 (at 12V) = 2 V0 + Vdrop = 26 V N2 (at 12V) = 11.9 turns.

Choose N2 (at 12V) = 12 turns

(Confirm the result by Pexpt)

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Difference

Parameter Calculation PExpt % Difference

V1(V) 110 110 /

V2(V) 12 13.6 11.7%

N1(turn) 102 100 2%

N2(turn) 5.4 5.0 8%

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*Half bridge Forward converter:

This design is very similar to the method use for

the forward converter example.

Figure 2.11.1 - Typical core section graph

P = 100W at fs50 kHz.

Vi = 85 137 V (nominal 110V).

Vo = 5V and Io = 20 A (100W).

V1 = Vi x (1.3) x (1.9)V1min = 85 x (1.3) x (1.9) = 209V

V1nominal = 110 x (1.3) x (1.9) = 272V

V1max = 137 x (1.3) x (1.9) = 338V

-Core size: Use figure 2.11.1, at 100W .

We choose core type EC 41.Core parameter: core area Ae=120 mm

2

-Optimum induction: Use figure 2.9.1 at

100W and f=50kHz.

Bopt= 85 mT ( for P.P )

For half bridge, we choose the max. flux density

Bm=210mT.

[ Bm = (85 x 2) .nomV

V

1

max1

= 210mT ]

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Figure 4 - Multiple output application

N21

D3

D4 C2

L2

N22

D5

D6C3

L3

N2

D1

D2C1

L1

+12v

-12V

COMMON

+5v

N1

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CORE CONSIDERATION:

Related formulas:

Vd = N1dt

d; Vd = N1

ont

max

max = 2Bmax Ae =1

ond

N

t.V

(Bmax = 2B)

Bmax =sw.e.1

d

fA4N

V(ton =

swf

D; D = 0.5)

For forward converter:

Bmax < 0.5 (Bm Br) Bm = Bsat

-A large value of Bm allows Bmax large

result to smaller Ae. Therefore, smaller

core size.

-Higher switching frequency result in

smaller core size.

(However fsw> 100kHz result in a smaller value

ofBmax to be chosen to limit the core losses).

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Advantage

- Isolate the output from the input electrically.

- Smaller core size.

- Provide a multiple output voltage.

- Low cost.

The design for the DC power supplies is

very necessary.

*Conclusion

Transformer is designed in almost AC to DC

and DC-DC converter. It is an importantdevice in the DC power supply. Specially,

in dc-dc converter, transformer has a small

size and therefore a low cost.

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CONCLUSION:

Transformer is designed in almost AC to

DC and DC-DC converter. It is an

important device in the DC power supply.

Specially, in dc-dc converter, transformerhas a small size and therefore a low cost.

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A list of References:

1- Switch mode power supply handbook by Keith Billing, 2nd

Edition.Mc Graw Hill, 1999.

2- Power Electrics: Converter, Application and Design, Mohan,

Undeland and Robbin, Willey, 1989.

3- Introduction to Power Electronic by Daniel W. Hart, Prentice

Hall,

Inc. 1997.4- Lecture note Power Electric by Prof. D. Zhou, Ph. D. (2003).

5- Http://www.power

designers.com/infoweb/disg/converter.sht.

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