Advanced topologies Half-bridge, Full-bridge, Push-Pull, Cuk, SEPIC - - PDF document

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Mor M. Peretz, Switch-Mode Power Supplies

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Advanced topologies

Half-bridge, Full-bridge, Push-Pull, C’uk, SEPIC

• C’uk
• Sepic
• Half-bridge
• Symmetrical operation
• Double power supply
• Principle of operation , definition of D
• Using bus capacitors – capacitive voltage division?
• The concept of split bus capacitor
• Component stress
• Asymmetrical operation
• Full-bridge
• Operation
• Stress
• Reset
• Push-pull

Mor M. Peretz, Switch-Mode Power Supplies

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Types of PWM converters C’uk and SEPIC

C’uk SEPIC

Co Vin Ro L1 L2 C Vo Q D

D 1 D V V

in

• 

  D 1 D V V

in

• 



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Mor M. Peretz, Switch-Mode Power Supplies

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C’uk Converter

Voltage

• f C1 constant

1 2 1

• in

c in

• V

V V V V V V    

1

( )

• c
• n
• in
• n
• n

in

• ff

V V D V V V D V D V D         

(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 Mor M. Peretz, Switch-Mode Power Supplies

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C’uk with isolation

C1a L2 L1 S D C2 R Vout V2 Vin C1b 1:n

 Any polarity  Any voltage ratio

• n

in

• ff

V D n V D  

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Mor M. Peretz, Switch-Mode Power Supplies

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C’uk Converter

Inductors on the same core

Can be done only if the voltage on the windings are equal

C1 L2 L1 S D C2 R Vout V1 V2 VC1 Vin Mor M. Peretz, Switch-Mode Power Supplies

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Advantages

 Continues 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 

C’uk advnatages and disadvantages

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Mor M. Peretz, Switch-Mode Power Supplies

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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

1 2 1 L L C in

V V V V   

x

• ff

in

• n
• n

in

• ff

V V D V D V D V D      

ON OFF

Mor M. Peretz, Switch-Mode Power Supplies

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Half-bridge

HB, symmetrical operation

1 2

• in

V n D V n 

Ts Q1 Q2 T1 Vx Vx Ton Ton

2

• n

s

t D T 

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Mor M. Peretz, Switch-Mode Power Supplies

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Half-bridge

What is the transformer voltage at off time

Ts Q1 Q2 T1 Vx Vx Ton Ton

Mor M. Peretz, Switch-Mode Power Supplies

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Types of PWM converters

HB –Capacitors to replace supplies

C2 C1 Q2 +Vin Q1 n1

Vx

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Mor M. Peretz, Switch-Mode Power Supplies

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Types of PWM converters

HB -Concept of split bus capacitors

C2 C1 Q2 +Vin Q1 n1

Vx

Mor M. Peretz, Switch-Mode Power Supplies

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Types of PWM converters

Asymmetrical operation – synchronous rectifier

C2 C1 Q2 +Vin Q1 n1

Vx

Motivation to asymmetrical operation: Spikes and

• scillations at the mid point an off time

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Mor M. Peretz, Switch-Mode Power Supplies

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Full-bridge

1 2 2

• in

V n D V n 

Mor M. Peretz, Switch-Mode Power Supplies

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Push-pull

1 2 2

• in

V n D V n 

Ts Q1 Q2 Ton Ton

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Mor M. Peretz, Switch-Mode Power Supplies

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Reset of Forward, HB, FB

 Forward - auxiliary winding  HB,FB - Natural

t

1

V ton ton 2 TS 2 TS 2 VC 2 VC 

L C R Vx Vo T n V2

S1 S2 V1 T C1 C2 VC Mor M. Peretz, Switch-Mode Power Supplies

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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

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Mor M. Peretz, Switch-Mode Power Supplies

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t ton t toff IS VS IHB =2IFW

C

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

Waveforms

Mor M. Peretz, Switch-Mode Power Supplies

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Types of PWM converters Comparison chart

Converter Sw current Sw voltage Buck Io Vin Boost Io(Don/Doff) Vo Buck-Boost Io(Don/Doff) Vin+Vo C’uk Iin+Io Vin+Vo SEPIC Iin+Io Vin+Vo Forward Io*(n2/n1) Vin+Vrst Flyback Io*(n2/n1)(Don/Doff) Vin+Vo*(n1/n2) HB 2Io *(n2/n1) Vin FB Io *(n2/n1) Vin/2 PP Io *(n2/n1) 2Vin

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Mor M. Peretz, Switch-Mode Power Supplies

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Mor M. Peretz, Switch-Mode Power Supplies

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Mor M. Peretz, Switch-Mode Power Supplies

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Mor M. Peretz, Switch-Mode Power Supplies

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