EN 710 – Switching Power Supplies Fall 2014, Heldenfels 105

Harish Krishnamoorthy

(hsk@tamu.edu)

Lecture 4: CUK and SEPIC CONVERTERS

9/15/2014

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Buck Converter

Boost Converter

Buck/Boost Converter

𝑉𝑜 = 𝐷. 𝑉𝑔

𝑉𝑜 =1

(1 − 𝐷). 𝑉𝑔

𝑉𝑜 =−𝐷

(1 − 𝐷). 𝑉𝑔

Basic DC-DC Converters: Comparison Under CCM

Buck Converter

Boost Converter

Buck/Boost Converter

Conventional DC-DC Converters – Points to Ponder

• Simple construction

• Voltage/Current Ratings?

• 2nd order systems

• Discontinuous input / output

currents

• Odd number of RHP zeros in

the transfer function in

boost and buck-boost

converters

Cuk Converter (Non-Isolated)

• “Cuk DC-to-DC switching converter with input current

shaping for unity power factor operation”, US 5442539A

- by Slobodan Cuk, Milivoje Brkovic; Caltech, 1992

- Reference: http://ecee.colorado.edu/copec/book/slides/Ch2slides.pdf

Cuk Converter - Introduction

• Essentially a boost converter followed by a buck-boost

• 4th order system, continuous input/output currents

• Inverted output voltage

Cuk Converter - Operation

- Reference: http://nptel.ac.in/courses/108105066/PDF/L-24(DK&SSG)(PE)%20((EE)NPTEL).pdf

Vo

Cuk Converter – Passives’ Design

- Reference: http://nptel.ac.in/courses/108105066/PDF/L-24(DK&SSG)(PE)%20((EE)NPTEL).pdf

Vo

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Cuk Converter – Other References

*Reference: D.C. Hamill, P.T. Krein, “A Zero

ripple technique applicable to any dc

converter”, IEEE PESC Conference, 1999, pp

1165-1171

SEPIC Converter

• Single-ended primary-inductor converter

• SEPIC - a boost converter followed by a buck-boost

• Non-inverting output and better short circuit protection

• 3 RHP zeros!

• http://www.maximintegrated.com/en/app-notes/index.mvp/id/1051

• http://users.ece.utexas.edu/~kwasinski/_8_EE462L_DC_DC_SEPIC.pdf

SEPIC Converter – Operation (AN-1484)

• How to design the passive

components?

• What about the component

ratings??

DC-DC Converter – Loss Model

http://electronicdesign.co

m/power/fundamentals-

buck-converter-efficiency

Buck Converter – Synchronous Rectification

• Fast body diodes!

• Mostly lateral MOSFETs –

symmetrical structure

• Better Efficiency – Why?

• Can IGBTs work?

• Mind discontinuous

conduction!!!

Thanks!

9/16/2014

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Interesting reference for the future classes:

http://www.ee.bgu.ac.il/~kushnero/temp/guamicuk.pdf