1 Prof. S. Ben-Yaakov , Dc-DC Converters [7- 4] Full Bridge FB L - - PDF document

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• 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]

Buck derived topologies

Forward - one switch Half Bridge HB - two switches Full Bridge FB - four switches

t VX TS ton

S Vin D L C R Vx Vo

Buck topology

• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 3]

Half Bridge HB

S1 S2 V1 VC 2 VC 2 T S1 S2 t ton t ton t t t V1 V2 VX L C R Vx Vo T n V2 Frequency at output twice fs Output section: Buck

HB Characteristics:

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• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 4]

Full Bridge FB

S1 S2 L C R Vx Vo T T n V2 S3 S4 VC 1 C

S1 S2 t t S3 S4 t t TS

• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 5]

Reset of Forward, HB, FB

Forward - auxiliary winding HB,FB - Natural C1, C2 capacitor divider

t

1

V ton ton 2 TS 2 TS 2 VC 2 VC −

Example HB

L C R Vx Vo T n V2 S1 S2 V1 T C1 C2 VC

• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 6]

Push-Pull

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• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 7]

Forward, HB, FB, PP

IL ripple for same L

Forward: HB, FB, PP:

2 I ∆ I ∆ Switch Utilization Important consideration: Vs(off), Is(on) Assumption:

Same input and output power Same input voltage

t ton t toff IS VS IFW       +

• ff
• n

C

D D 1 V

FORWARD

• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 8]

t ton t toff IS VS IHB =2IFW

C

V t ton t toff IS VS IFB =IFW VC HB FB

Waveforms

• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 9]

IS V FW 1

Doff Don

1+

HB 2 1 PP 1 2 FB 1 1

Power conversion capability:

FW<HB<FB

Stresses

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• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 10]

Topology selection

• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 11]

Cuk Converter

Voltage

• f C1≈ constant
• in

1 c in 2

• 1

V V V V V V V − = = =

• ff
• n

in

• n
• in
• n

1 c

• D

D V V D ) V V ( V D V V − = ⋅ − − = ⋅ − =

(buck) ON OFF

C1 L2 L1 S D C2 R Vout V1 V2 VC1 Vin C1 L2 L1 C2 R Vout Vin C1 L2 L1 C2 R Vout Vin

• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 12]

Cuk with isolation

C1a L2 L1 S D C2 R Vout V2 Vin C1b 1:n Any polarity Any voltage ratio

n D D V V

• ff
• n

in

• ±

=

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• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 13]

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 High voltage on switch

• ut

in

V V +

Cuk advnatages and disadvantages

• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 14]

SEPIC Converter

Vin L1 L2 D C1 S C2 R Vout Vx Vin L1 L2 C1 S C2 R Vx

Vin L1 L2 C1 S C2 R Vx D

in 1 C 2 L 1 L

V V V V = = =

• ff
• n

in

• n

in

• ff
• x

D D V V D V D V V = = ⋅ − ⋅ = ON OFF

• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 15]

Auxiliary output

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• 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

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• Prof. S. Ben-Yaakov , Dc-DC Converters

[7- 19]

Synchronous rectifier

VOLTAGE REGULATION MODULE (VRM)