Circuits and methods for driving light sources
Embodiments in accordance with the present invention provide circuits and methods for driving light sources, e.g., a light-emitting diode (LED) light source. In one embodiment, a lamp includes a rectifier rectifying an AC voltage to a rectified AC voltage, an LED light source, and a switch coupled to the LED light source in series controlling a current through the LED light source according to a predetermined current reference. The LED light source and the switch coupled in series receive the rectified AC voltage while the switch is controlled linearly.
1. A lamp comprising:
a rectifier operable for rectifying an AC voltage to a rectified AC voltage;
a light-emitting diode (LED) light source, wherein a terminal of said LED light source receives said rectified AC voltage; and
a switch coupled to said LED light source in series and operable for controlling a current through said LED light source according to a predetermined current reference, wherein said switch is controlled linearly, wherein said LED light source is powered on and regulated when a signal indicative of said rectified AC voltage is greater than a DC voltage, and wherein said LED light source is powered off when said signal indicative of said rectified AC voltage is less than said DC voltage, wherein said DC voltage is proportional to an average level of said rectified AC voltage.
2. A controller operable for controlling power to a light-emitting diode (LED) light source which receives a rectified AC voltage, said controller comprising:
a first switch coupled to said LED light source in series; and
control circuitry coupled to said first switch and operable for comparing a sensing signal indicative of a current through said LED light source to a reference signal indicative of a current reference and operable for generating a control signal to control said first switch linearly,
wherein said controller powers on said LED light source when a signal indicative of said rectified AC voltage is greater than a DC voltage, and wherein said controller powers off said LED light source when said signal indicative of said rectified AC voltage is less than said DC voltage, wherein said control circuitry controls said first switch linearly when said signal indicative of said rectified AC voltage is greater than said DC voltage, and wherein said control circuitry turns off said first switch when said signal indicative of said rectified AC voltage is less than said DC voltage, wherein said controller further comprises:
a second switch coupled to said control circuitry and said first switch, operable for controlling said first switch; and
a comparator operable for generating a control signal to control said second switch by comparing said signal indicative of said rectified AC voltage to said DC voltage, wherein said first switch is turned off by said second switch when said signal indicative of said rectified AC voltage is less than said DC voltage.