Susie Maestre

user Electronics Engineer

city Innovuze Solutions Inc.

  • Buck-Boost LED Driver with PWM Dimming

  • Created: Mar 29, 2016

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The LED drivers are electrical devices that regulate the power to an LED or strings of LEDs. It provides a constant quantity of power to the LED as its electrical properties change with temperature. The LED drivers are necessary to rectify higher voltage, alternating current to low voltage, direct current. It also protects LEDs from voltage or current fluctuations. A change in voltage can cause a change in the current being supplied to the LEDs. The LED light output is proportional to its current supply, and LEDs are rated to operate within a certain current range. Therefore, too much or too little current can cause light output to vary or degrade faster due to higher temperatures within the LED.

This design utilizes LTC3783, which is a current mode LED driver and boost, flyback and single-ended primary inductor converter (SEPIC). This drives both an N-channel power MOSFET and an N-channel load PWM switch. This design also uses the Fairchild’s FDMS86181 N-channel power MOSFET. This incorporates shielded gate technology and is optimized to minimize on-state resistance. The LTC3783, in this design, senses the voltage across the power MOSFET by connecting the SENSE pin to a conventional shunt resistor in the source of the power MOSFET. Sensing the voltage across the power MOSFET maximizes converter efficiency and minimizes the component count, but limits the output voltage to the maximum rating for this pin (36V). By connecting the SENSE pin to a resistor in the source of the power MOSFET, the user is able to program output voltages significantly greater than 36V, limited only by other components’ breakdown voltages.

This design is useful in a wide range of applications especially in the areas of automotive systems and industrial control. It is also useful in telecom power supplies, high voltage LED arrays and phone power supplies.



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