Abstract: The present invention is an apparatus for driving white LEDs. The apparatus includes a switchable current sink, a DC-DC converter and a reference circuit. The DC-DC converter provides a driving voltage to a plurality of LEDs. The switchable current sink regulates currents through the plurality of LEDs, and the switchable current sink further provides a first reference voltage and outputs a plurality of voltage drops. The reference circuit receives the first reference voltage and the plurality of voltage drops to provide a second reference voltage to the DC-DC converter. The DC-DC converter adjusts the driving voltage provided to the plurality of LEDs according to the second reference voltage. In this way, the driving voltage is regulated to a minimum possible value and consequently the voltage drops across the switchable current sink is minimized. Hence, the LED driving system maintains higher efficiency.

Abstract: In one embodiment, a current sensing circuit for a converter includes a sensing switch and a comparator. The sensing switch is coupled to a power switch within the converter for receiving a first voltage signal indicative of the current through the power switch. The sensing switch also produces a second voltage signal based on the first voltage signal. The comparator is coupled to the sensing switch for detecting an operation condition of the converter based on the second voltage signal. An offset voltage between the second voltage signal and the first voltage signal can compensate for a delay at the comparator.

Abstract: A method for using a single pin to support both power input and power control functions for an integrated circuit, wherein the integrated circuit is in communication with a system. The method includes receiving at the pin a power input signal from the system, generating a power control signal based on the power input signal through a control signal generating circuit, and sending the power control signal to the integrated circuit.

Abstract: The present invention is an apparatus for driving white LEDs. The apparatus includes a switchable current sink, a DC-DC converter and a reference circuit. The DC-DC converter provides a driving voltage to a plurality of LEDs. The switchable current sink regulates currents through the plurality of LEDs, and the switchable current sink further provides a first reference voltage and outputs a plurality of voltage drops. The reference circuit receives the first reference voltage and the plurality of voltage drops to provide a second reference voltage to the DC-DC converter. The DC-DC converter adjusts the driving voltage provided to the plurality of LEDs according to the second reference voltage. In this way, the driving voltage is regulated to a minimum possible value and consequently the voltage drops across the switchable current sink is minimized. Hence, the LED driving system maintains higher efficiency.

Abstract: The present invention is an apparatus with balance-dimming capability for controlling the brightness of keypad backlight. The keypad backlight includes a plurality of light emitting diodes (LEDs). The apparatus includes a switch and a pulse-width modulation (PWM) generator. The switch is coupled between a power supply and the plurality of LEDs. The PWM generator is coupled to the power supply and the switch, and is capable of generating a PWM signal and controlling the brightness of the plurality of LEDs.

Abstract: A method for using a single pin to support both power input and power control functions for an integrated circuit, wherein the integrated circuit is in communication with a system. The method includes receiving at the pin a power input signal from the system, generating a power control signal based on the power input signal through a control signal generating circuit, and sending the power control signal to the integrated circuit.