LED DESIGN FORUM: Hybrid control techniques drive different LED applications (MAGAZINE)

Aug. 4, 2009
The different demands of LED lighting and automotive applications require hybrid control methods to take advantage of the strengths of hysteretic and current-mode control, writes James Patterson.
As high brightness (HB) LEDs continue to evolve, and the world’s energy conscience focuses in on lighting, there becomes a greater need for efficient, long-lasting drive circuitry. Creating a robust, efficient HB-LED driver requires analysis of the end application. The designer often has some flexibility in either the input or output specifications, therefore the driver topology and control method should be determined by weighing the advantages and disadvantages of each possible configuration.

With any HB-LED driver, the output should be a regulated current source that can provide the necessary output voltage to the string(s) of LEDs. Though linear regulators are cheap and small, design limitations and poor efficiency usually make them non-ideal for driving HB-LEDs. In general, a switching regulator will be the best choice.

Deciding on a topology
A power MosFET, diode and inductor form a three-terminal network which is the basis for all switching regulators. There are three basic topologies derived from this network using different input/output configurations: buck (step-down), boost (step-up) and buck-boost (step-up/down). The switching regulator topology is chosen based on the specific application.


This article was published in the July/August 2009 issue of LEDs Magazine.

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