Active LED voltage clamp

摘要

An active clamp current sink is used to voltage protect a low voltage rated, high power current sink that drives illumination current through a string of serially connected LEDs. When the LEDs are turned off as part of a PWM configuration, the forward voltage on the LEDs falls, and the voltage presented to the low voltage rated, high power current sink rises. The active clamp current sink monitors the voltage across the high power current sink and ensures that an adequate current flows through the LEDs. This minimally adequate current maintains a sufficiently large forward voltage through the LEDs, and therefore a sufficiently small voltage is presented to the high power current sink.

主权项

1. An integrated circuit for controlling one or more LED strings, each of the one or more LED strings having an anode connected to a power supply and a cathode, the integrated circuit comprising:
a first pin constructed to connect to a source terminal of an external MOSFET separate from the integrated circuit; a second pin constructed to connect to a gate terminal of the external MOSFET; a third pin constructed to connect to a drain terminal of the external MOSFET and the cathode of each LED string of the one or more LED strings; and an active clamp current sink including an internal MOSFET and an amplifier, the active clamp current sink configured to maintain a voltage level at the cathode of each LED string of the one or more LED strings below a maximum voltage of the external MOSFET during periods of time in which the external MOSFET is turned off by shunting current away from the external MOSFET and through the internal MOSFET.