Boost Converter ICs Step Up To The Plate Sponsored by: NATIONAL SEMICONDUCTOR

Feb. 3, 2005

What are the types of boost converter topologies? Primarily, boost converter ICs are used in battery-operated or portable electronic devices to "boost" or "step-up" the battery voltage to a higher level. These non-isolated converters employ an indu

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What are the types of boost converter topologies?

Primarily, boost converter ICs are used in battery-operated or portable electronic devices to "boost" or "step-up" the battery voltage to a higher level. These non-isolated converters employ an inductor. Also, there is a galvanic path between the input and output. A charge pump (switched capacitor) converter would be another transformer-less approach. Here, we will only consider the switch-mode boost converter. We'll cover the charge pump boost converter in a future edition of Power Design FAQs.

Do isolated boost converter topologies exist?

Isolated step-up converters employ a flyback (buck-boost) or forward converter (buck) topology. Isolation requires a transformer, so any desired step-up or step-down ratio depends on the transformer turns ratio.

How does the basic transformer-less switch-mode boost converter IC work?

In the basic boost IC circuit, closing the switch allows current to build up in the inductor (Fig. 1). When the switch opens, the stored inductor energy freewheels into the output through the boost diode. After several switching cycles, the steady dc output voltage developed across the output capacitor is higher than the input voltage.

What determines the output voltage of the boost dc-dc converter?

In the more detailed circuit in Figure 2, a power MOSFET replaces the mechanical switch. A pulse-width modulator (PWM) control circuit drives the MOSFET to ensure a constantly regulated output. The duty cycle determines the output voltage, which is the ratio of the switch on-time to the entire switching cycle time. For a 50% duty cycle, the calculated output voltage is approximately twice the input voltage.

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About the Author

Sam Davis 2

Sam Davis was the editor-in-chief of Power Electronics Technology magazine and website that is now part of Electronic Design. He has 18 years experience in electronic engineering design and management, six years in public relations and 25 years as a trade press editor. He holds a BSEE from Case-Western Reserve University, and did graduate work at the same school and UCLA. Sam was the editor for PCIM, the predecessor to Power Electronics Technology, from 1984 to 2004. His engineering experience includes circuit and system design for Litton Systems, Bunker-Ramo, Rocketdyne, and Clevite Corporation. Design tasks included analog circuits, display systems, power supplies, underwater ordnance systems, and test systems. He also served as a program manager for a Litton Systems Navy program.

Sam is the author of Computer Data Displays, a book published by Prentice-Hall in the U.S. and Japan in 1969. He also authored the book Managing Electric Vehicle Power. He is also a recipient of the Jesse Neal Award for trade press editorial excellence, and has one patent for naval ship construction that simplifies electronic system integration.

You can also check out additional articles on his other author page.