Light-emitting diode lighting device having multiple driving stages and line/load regulation control
An LED lighting device includes multiple luminescent devices driven by a rectified AC voltage. The multiple luminescent devices are turned on flexibly in a multi-stage driving scheme using multiple current controllers. The current settings of the two driving stages with the highest current level and the second highest current level are adjusted according to the variation in the rectified AC voltage V AC or according to the variation in the duty cycle of the luminance device due to the variation in the rectified AC voltage. The present invention can improve the line/load regulation of the LED lighting device when the rectified AC voltage somehow fluctuates between its upper bound and lower bound.
1. A light-emitting diode (LED) lighting device having multiple driving stages, comprising:
a first luminescent device driven by a rectified alternative-current (AC) voltage for providing light according to first current;
a second luminescent device coupled in series to the first luminescent device and driven by the rectified AC voltage for providing light according to second current;
a voltage detector configured to monitor a variation in a peak level of the rectified AC voltage and generate a compensation voltage associated with the peak level of rectified AC voltage;
a first current controller coupled in parallel with the first luminescent device and configured to:
regulate the first current so that the first current does not exceed a first current setting; and
adjust the first current setting according to the compensation voltage; and
a second current controller coupled in series to the second luminescent device and configured to:
regulate the second current so that the second current does not exceed a second current setting; and
adjust the second current setting according to the compensation voltage.
2. The LED lighting device of claim 1 , wherein:
the first current controller includes:
a first switch configured to conduct third current according to a first control signal;
a current detector configured to monitor a sum of the first current and the third current and provide a corresponding feedback voltage;
a first reference voltage generator configured to provide a first reference voltage associated with the first current setting and adjust the first reference voltage according to the compensation voltage; and
a first comparator configured to generate the first control signal according to a relationship between the first reference voltage and the feedback voltage; and
the second current controller includes:
a second switch configured to conduct the second current according to a second control signal;
a second reference voltage generator configured to provide a second reference voltage associated with the second current setting and adjust the second reference voltage according to the compensation voltage; and
a second comparator configured to generate the second control signal according to a relationship between the second reference voltage and the feedback voltage.
3. The LED lighting device of claim 2 , wherein a durability of the second switch is higher than a durability of the first switch.
4. The LED lighting device of claim 2 , further comprising a line/load regulation compensation control unit configured to operate the first reference voltage generator and the second reference voltage generator according to the compensation voltage so that the first reference voltage or the second reference voltage is adjusted to a first value when the compensation voltage is equal to a second value or is adjusted to a third value when the compensation voltage is equal to a fourth value, wherein the first value is larger than the third value and the second value is smaller than the fourth value.
5. The LED lighting device of claim 4 , wherein the first switch, the first comparator, the first reference voltage generator, the second comparator, the second reference voltage generator and the line/load regulation compensation control unit are integrated into a same chip.
6. The LED lighting device of claim 1 , further comprising a power supply circuit configured to provide the rectified AC voltage, wherein the voltage detector is coupled to the power supply circuit for detecting the peak level of the rectified AC voltage during each driving cycle.
7. The LED lighting device of claim 1 , wherein the voltage detector is coupled to the second luminance device for detecting a variation in a conducting duty cycle of the second luminance device due to a variation in the rectified AC voltage.
8. The LED lighting device of claim 1 , further comprising:
a third luminescent device coupled in series to the first and second luminescent devices and driven by the rectified AC voltage for providing light according to fourth current.
9. The LED lighting device of claim 8 , wherein the third luminescent device is coupled between the rectified AC voltage and the first luminescent device.
10. The LED lighting device of claim 8 , further comprising:
a third current controller coupled in parallel with the third luminescent device and configured to regulate the fourth current so that the fourth current does not exceed a third current setting, wherein the third current setting is a constant value.