EE-464 STATIC POWER CONVERSION-II

Switching Power SuppliesOzan Keysan

keysan.me

O�ce: C-113 • Tel: 210 7586

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Regulated Power Supplies

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Regulated Power SuppliesRegulated Output Voltage

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Regulated Power SuppliesRegulated Output Voltage

Electric Isolation

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Regulated Power SuppliesRegulated Output Voltage

Electric Isolation

Minimum size, weight

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Regulated Power SuppliesRegulated Output Voltage

Electric Isolation

Minimum size, weight

Minimum cost

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Regulated Power SuppliesRegulated Output Voltage

Electric Isolation

Minimum size, weight

Minimum cost

Maximum e�ciency

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Linear Regulators

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Linear Regulators

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Linear Power Supplies

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Linear Power Supplies

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Linear Power Supplies

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Linear Power SuppliesLow frequency transformer: large and heavy

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Linear Power SuppliesLow frequency transformer: large and heavy

BJT operates in linear region: dissipates heat

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Linear Power SuppliesLow frequency transformer: large and heavy

BJT operates in linear region: dissipates heat

E�ciency is around 30-60%

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Linear Power SuppliesLow frequency transformer: large and heavy

BJT operates in linear region: dissipates heat

E�ciency is around 30-60%

Advantage:

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Linear Power SuppliesLow frequency transformer: large and heavy

BJT operates in linear region: dissipates heat

E�ciency is around 30-60%

Advantage:Minimum EMI Problems

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Switching DC Power Supply

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Switching DC Power Supply

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Switching DC Power Supply

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Switching DC Power SupplyMultiple Output Case

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Case Study:

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Case Study:Apple Charger Teardown

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Apple Charger Teardown

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Flyback Converter

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Flyback Converter Evolution

Start from the buck-boost converter

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Flyback Converter Evolution

Wound the inductor with two parallel wires

Don't get confused with the dots yet!

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Flyback Converter Evolution

Isolate inductor wires (isolated converter)

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Flyback Converter Evolution

Modify turns ratio to adjust output voltage anddirection to get positive output

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Back to EE361

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Back to EE361Ideal Transformer

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Back to EE361Ideal Transformer

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Back to EE361Ideal Transformer

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Back to EE361

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Back to EE361Realistic Transformer Equivalent Circuit

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Back to EE361Realistic Transformer Equivalent Circuit

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Flyback ConverterLet's ignore resistive parts and leakage �ux for now

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Flyback Converter with Transformer

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Flyback Converter with Transformer

Can you plot the operating modes?

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Flyback ConverterSwitch ON

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Flyback ConverterSwitch OFF

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Flyback Converter

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Flyback Converter

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Flyback ConverterConversion ratio can be calculated in three di�erent ways:

Magnetic Circuit: Transformer Flux

Steady state current

Graphically: Voltage-seconds area of the inductor

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Flyback ConverterConversion ratio can be calculated in three di�erent ways:

Magnetic Circuit: Transformer Flux

Steady state current

Graphically: Voltage-seconds area of the inductor

=Vo

Vd

D

(1 −D)

N2

N1

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Switch Selection

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Switch Selection

Peak Switch Current

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Switch Selection

Peak Switch Current

= +I sw

1

(1 −D)

N2

N1Io

N1

N2

(1 −D)Ts

2Lm

Vo

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Switch Selection

Peak Switch Current

Peak Switch Voltage

= +I sw

1

(1 −D)

N2

N1Io

N1

N2

(1 −D)Ts

2Lm

Vo

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Switch Selection

Peak Switch Current

Peak Switch Voltage

= +I sw

1

(1 −D)

N2

N1Io

N1

N2

(1 −D)Ts

2Lm

Vo

= +V sw Vd

N1

N2Vo

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Switch Selection

Peak Switch Current

Peak Switch Voltage

= +I sw

1

(1 −D)

N2

N1Io

N1

N2

(1 −D)Ts

2Lm

Vo

= +V sw Vd

N1

N2Vo=

Vd

(1 −D)

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Flyback Converter: DCM

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Reading MaterialsThe Flyback Converter

Flyback transformer tutorial: function and design

Flyback Converter Video

Designing a DCM �yback converter

Flyback DCM vs CCM

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Flyback Variations: Two Transistor Flyback

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Flyback Variations: Two Transistor Flyback

Improv�ng the Performance of Trad�t�onal Flyback w�th Two Sw�tch Approach

Operat�on & Benef�ts of Two-Sw�tch Forward/Flyback Power ConverterTopolog�es

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Flyback Variations: Paralled Flyback

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Flyback Variations: Paralled Flyback

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Forward Converter

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Forward ConverterDerived from the Buck Converter

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Forward ConverterLet's obtain the output voltage characteristics

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Forward ConverterA buck converter with added turns ratio

= DVo

Vd

N2

N1

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Forward Converter

What happens at the instant when the switch isturned-o�, if the transformer is not ideal?

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Forward Converter

A discharging path for Lm should be added.

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Simple Solution: RCD Reset Circuit

Magnetizing current dissipates through RCD circuit36 / 70

Simple Solution: RCD Reset Circuit

Cheap but ine�cient37 / 70

RCD SnubberNote a similar circuit can be used for the Flyback converter (to reduceinductance leakage ringing)

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RCD SnubberNote a similar circuit can be used for the Flyback converter (to reduceinductance leakage ringing)

Suggested Reading: Flyback Converter Snubber Design

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Practical Forward Converter

A transformer with two-primary windings

Third winding is added to discharge the energy stored in Lm

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Practical Forward Converter

A transformer with two-primary windings

Third winding is added to discharge the energy store

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Forward Converter

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Forward Converter: Switch is ON

Lm is charged by input voltage, Lx is also charging

D1 On, D2 O�, D3 O�

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Forward Converter: Switch is OFF

Lx feeds the load, Lm is discharged to the source:

KCL:

For proper operation the transformer should be "reset" before nextON period

= −i1 iLm

= −N1i1 N2i2 N3i3

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Forward Converter: Switch is OFF

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Forward Converter

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Forward Converter

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Practical Forward ConverterFor proper operation the transformer should be "reset" before nextON period

< (1 − D)tm Ts

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Practical Forward ConverterFor proper operation the transformer should be "reset" before nextON period

< (1 − D)tm Ts

Dmax

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Practical Forward ConverterFor proper operation the transformer should be "reset" before nextON period

< (1 − D)tm Ts

Dmax=1

1 + ( / )N3 N1

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What happens if D is large, and transformer does not resetcompletely?

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What happens if D is large, and transformer does not resetcompletely?

In the f�gure Dmax=0.5

Saturation, increased core losses, reduced Lm, problem in powertransfer 48 / 70

Advantages over FlybackBetter utilization of transformer (direct powertransfer, higher)

A gapless core can be used (higher Lm, less ripple)

Output inductor and diode ensures continuousoutput current

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Drawbacks compared to FlybackIncreased cost (extra diode and inductor)

Gain changes a lot in DCM

Higher voltage requirement for MOSFET

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Forward Converter Alternatives

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Forward Converter AlternativesTwo-switch forward converter

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Forward Converter AlternativesTwo-switch forward converter

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Two-switch forward converterAdvantages:

Does not require a snubber circuit

Less voltage stress on MOSFETs

Can supply multiple isolated outputs

Low power losses and noise

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Two-switch forward converter

Disadvantages:

Slightly more expensive

Larger component count

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Interleaved forward converter

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Forward Converter Reading MaterialsIn�neon, Forward Converter Design Note

Fairchild Forward Converter Application Note

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Example:Hart - Power Electronics

Ex. 7-4

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Push-Pull Converter

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Push-Pull Converter

Uses a center-tapped transformer 58 / 70

Push-Pull Converter

Three operating sections

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Push-Pull ConverterSwitch(T1) ON, Switch(T2) OFF

D1 conducts, D2 reverse-biased

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Push-Pull ConverterSwitch(T1) ON, Switch(T2) OFF

D1 conducts, D2 reverse-biased

=vxN2

N1Vs

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Push-Pull ConverterSwitch(T1) ON, Switch(T2) OFF

D1 conducts, D2 reverse-biased

increases linearly

=vxN2

N1Vs

= − = −vL vx Vo

N2

N1Vs Vo

iL

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Push-Pull ConverterSwitch(T2) ON, Switch(T1) OFF

Symmetrical operation with the previous

=vxN2

N1Vs

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Push-Pull ConverterSwitch(T2) ON, Switch(T1) OFF

Symmetrical operation with the previous

increases linearly

=vxN2

N1Vs

= − = −vL vx Vo

N2

N1Vs Vo

iL

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Push-Pull ConverterBoth Switches are OFF

for a period of Δ

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Push-Pull ConverterBoth Switches are OFF

for a period of

Both D1 and D2 conducts

Δ

= = 0.5ID1 ID2 IL

= 0vx

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Push-Pull ConverterBoth Switches are OFF

for a period of

Both D1 and D2 conducts

Therefore

Inductor discharges and feeds the load

Δ

= = 0.5ID1 ID2 IL

= 0vx

= −vL Vo

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Repeating waveforms for every Ts/2

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Push-Pull ConverterRepeating waveforms for every Ts/2

D + Δ =Ts

Ts

2

Δ =(1 − 2D)

2Ts

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Push-Pull ConverterOutput voltage characteristics?

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Push-Pull ConverterOutput voltage characteristics?

Use the inductor voltage

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Push-Pull ConverterOutput voltage characteristics?

Use the inductor voltage

Twice of the forward converter

= DVo

Vd

2N2

N1

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Push-Pull ConverterComparison of Magnetic Flux in the Core

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Extra MaterialsFlyback ConverterECEN4517 Lecture Notes

Flyback Transformer Tutor�al

Opt�m�sed Flyback Des�gn

Sw�tch Mode Power Supply (SMPS) Topolog�es

ECE5797 SMPSs

Flyback Converter, Transformer Des�gn

Des�gn Gu�de Flyback Converter

Des�gn Gu�del�nes for Flyback Converter

Transformer Design Cookbook 67 / 70

Extra MaterialsForward Converter

Forward Converter, Transformer, Inductor Design

Forward Converter Design

Forward Converter Tutorial Video

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Design Exercise

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Design ExerciseForward Converter Design

ETD 34/17/11

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Design ExerciseForward Converter Design

ETD 34/17/11

Skin E�ect Calculator

AWG Conductors

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You can download this presentation from:keysan.me/ee464

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