Simplified Analysis Of A DCM Boost Converter Driving An LED String Part II: Practical Considerations

Focus:

Part I of this article was dedicated to the theoretical analysis of a boost converter driving an LED string under DCM operation. This study was motivated by the need to stabilize the loop of an automotive LED backlight driver. As pulse width modulation is implemented for dimming control, loop control represents an important design consideration that conditions the final performance of the driver. Here in Part II, the authors describe an implemented solution for a dimmable LED driver based on ON Semiconductor’s NCV887300 nonsynchronous boost controller and verify the measured frequency response versus that calculated using the equations derived in Part I. The article begins by discussing key features of the controller, why the topology and various components were selected, and key aspects of circuit operation. Then measured and simulated results for circuit response are presented for the implemented LED drver design and the discrepancy due to a missing RHP zero is discussed. Finally operating waveforms are presented and system performance is discussed.

What you’ll learn:

• How to analysis the loop response of a dimmable LED driver based on a boost converter operating in discontinuous conduction mode

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Author & Publication:

Christophe Basso, ON Semiconductor, Toulouse, France and Alain Laprade, ON Semiconductor, East Greenwich, R . I ., How2Power Today, Mar 15 2013

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