Texas Instruments New Floating Switch Architecture for LED Lighting

AC switched matrix technique replaces flyback, buck and boost converters

Texas Instruments have released the industry's first floating switch architecture that simplifies the offline linear drive of LEDs in lamps, downlights and fixtures. The AC switched matrix technique features TI's TPS92411 floating MOSFET switc, is an innovative approach to producing low-ripple LED drive current without magnetic components. The architecture provides excellent compatibility with legacy wall dimmers and delivers high power factor and low total harmonic distortion (THD).

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Flyback, buck and boost converters are common switch-mode power supply (SMPS) topologies in LED lamps today. These circuits operate at high frequencies and require inductive components to turn mains AC current into the constant DC current necessary to drive LEDs. Selection of inductors and transformers for power transfer is complicated, often requiring expensive custom components. In addition, an electromagnetic interference (EMI) filter consisting of four to ten passive components is required to prevent the SMPS circuit from harming other electronic equipment. If phase dimming is required, multiple design iterations may be necessary to optimize dimmer compatibility and prevent LED flicker. The floating switch architecture with TI’s new TPS92411 overcomes these challenges. It requires no inductive components for power transfer, eliminating cost and bulk and simplifying design.

Features of the TPS92411 include:

100-V, 2-Ohm floating MOSFET switch with 350 mA of current capability
LED drive performance is comparable to traditional flyback, buck and boost converters:
- Greater than 0.95 power factor
- Less than 15 percent of total harmonic distortion
- Low LED current ripple results in efficient LED utilization as compared with "tapped linear" drivers
Low-frequency, slew-rate controlled switch action produces very little EMI noise
Unlike designs using traditional converters, the very low-cost floating switch architecture requires no inductive components
Works well with both TRIAC and reverse phase wall dimmers
Supports lighting designs up to 70W

More information on the TPS92411 Floating Switch for Offline AC Linear Direct Drive of LEDs, can be found on the TI website at TI TPS92411 product page

The Texas Instruments website address is www.ti.com
[Reprinted with kind permission from Texas Instruments]

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