Microsemi Corporation

Paul Okada

Dror Korcharz

Arkadiy Peker

Bruce Ferguson

An LED driver arrangement wherein a low voltage IC is arranged to sample the voltage at a terminal of each of the respective electronically controlled switches controlling a plurality of LED strings each receiving power from a single source, with the single source providing voltage in excess of the voltage rating of the IC. For each electronically controlled switch a controllable current source and an isolating unidirectional electronic valve is provided, the respective current source being enabled only when the respective associated electronically controlled switch is at least partially closed thereby ensuring that the respective isolating unidirectional electronic valve associated with the respective illuminating LED string conducts, and the voltage at the terminal of the respective electronically controlled switch is thus seen by the IC when the associated LED string is producing illumination, the voltage then being lower than the maximum voltage rating of the IC.

Sampling external voltage which may exceed integrated circuit maximum voltage rating

A secondary side voltage regulation scheme applied to a multiple output flyback converter. The output with the highest error voltage is selected to control the primary switch. The remaining outputs are regulated by varying the length of time that current is allowed to flow into each output by controlling the on time of a switch connected in series with each of the outputs. The switching of the windings is achieved using a single N channel MOSFET for each output. Regulation of the outputs is performed using leading edge modulation. The body diode of the output MOSFET switches are held off during the start of the commutation period by the use of an active clamp on the primary side.

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Foothill Ranch, CA, United States of America

Paul Okada