EN 710 – Switching Power Supplies Fall 2014, Heldenfels 105
Harish Krishnamoorthy
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!!!
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