Hardware

AN3151

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Doc ID 17051 Rev 1

Four DC-DC buck converters allow 4 LED strings to be driven, managing up to 120 W. From

a 48 DC input voltage the buck stage adapts the output voltage in order to drive the LEDs

with the imposed current. 3 W LEDs have been chosen in order to obtain 30 W per string,

covering the total power with 10 LEDs [4] in series on each string.

The buck stage works in continuous conduction mode (CCM) in order to minimize the

current ripple on the LEDs.

The inverse buck stage offers:

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Low voltage sensing circuitry

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Logic level MOSFETs driven by the microcontroller without a gate driver (ground

referred)

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High efficiency of up to 98 %

The LED current, to be measured by the microcontroller, is sensed by a ground referred

shunt resistor. This solution allows the current reading only when the MOSFET is on. This is

an important aspect to be evaluated for the current reading methodology to be described.