High efficiency white LED drivers

摘要

A circuit device for a high efficiency current driver for a white LED is presented. The circuit device includes a bias transistor to provide a substantially constant bias current through a bias leg. A driver transistor is connected to the bias transistor and the current in the driver transistor substantially matches the bias current. A current feedback amplifier is configured in series with the driver transistor and a feedback node has a feedback voltage representative of an output voltage. A mirroring transistor connected to the feedback node mirrors the output voltage to the bias transistor thereby allowing the output current to substantially match the bias current when an applied voltage across the driver transistor is below a saturation voltage of the driver transistor thus mitigating effects of headroom limitation in the driver transistor.