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A system having an alternating current (AC) driven LED unit, an AC voltage regulator, and a controller is provided. The AC driven LED unit includes a first LED and a second LED coupled in reverse parallel. The AC voltage regulator is operable to receive AC voltage originating from an AC voltage sour

A system having an alternating current (AC) driven LED unit, an AC voltage regulator, and a controller is provided. The AC driven LED unit includes a first LED and a second LED coupled in reverse parallel. The AC voltage regulator is operable to receive AC voltage originating from an AC voltage source, regulate the AC voltage according to control signals from the controller, and apply regulated AC voltage to the AC driven LED unit, so as to enable the first LED and the second LED to emit light according to the regulated AC voltage. In addition, a method is provided for driving the LED by regulating the AC voltage. By regulating the AC voltage using the AC voltage regulator, benefits of restraining voltage fluctuations, reducing THD, improving power factor, providing dimming control, and mitigating flicker phenomenon can be achieved.

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1. A system for driving light emitting diodes (LED), the system comprising: an alternating current (AC) driven LED unit, the AC driven LED unit comprising a first LED and a second LED, the first LED and the second LED being coupled in reverse parallel;an alternating current voltage regulator coupled

1. A system for driving light emitting diodes (LED), the system comprising: an alternating current (AC) driven LED unit, the AC driven LED unit comprising a first LED and a second LED, the first LED and the second LED being coupled in reverse parallel;an alternating current voltage regulator coupled between an AC voltage source and the AC driven LED unit; anda controller coupled to the AC voltage regulator, the controller configured to monitor AC voltage fluctuations of the AC voltage source and a regulated AC voltage supplied to the AC driven LED unit, and transmit control signals to the AC voltage regulator according to a monitored result,wherein the AC voltage regulator is operable to receive an AC voltage originating from the AC voltage source, and the AC voltage regulator is operable to regulate the AC voltage from the AC voltage source in response to the control signals transmitted from the controller, and to apply the regulated AC voltage to the AC driven LED unit, allowing the first LED and the second LED to emit light according to the regulated AC voltage;the controller is configured to monitor the AC voltage source for voltage fluctuation of the AC voltage from the AC voltage source and generate a first control signal to control the AC voltage regulator to maintain the regulated AC voltage from the AC voltage regulator supplied to the AC driven LED unit at a predetermined level; andthe controller is configured to monitor the AC driven LED unit to monitor a voltage fluctuation of the regulated AC voltage from the AC voltage regulator and generate a second control signal to control the AC voltage regulator to maintain the regulated AC voltage at the predetermined level. 2. The system of claim 1, wherein the AC voltage regulator comprises an AC chopper operable to selectively chop out at least a portion of the AC voltage from the AC voltage source according to a desired AC voltage to drive the AC driven LED unit so as to maintain the light emitted from the first LED and the second LED at a constant level. 3. The system of claim 2, wherein the AC chopper comprises a switch, the control signals transmitted from the controller comprise pulse signals, and the switch is capable of being turned on and off to regulate the AC voltage from the AC voltage source in response to the pulse signals supplied thereto. 4. The system of claim 3, wherein a voltage level of the regulated AC voltage applied to the AC driven LED unit is adjustable by varying a duty cycle of the pulse signals supplied to the switch, so as to achieve a dimming control of the first LED and the second LED. 5. The system of claim 2, wherein the AC chopper comprises a first switch and a second switch, the first switch is coupled in series between the AC voltage source and the AC driven LED unit, the second switch is coupled in parallel to the AC driven LED unit, the control signals transmitted from the controller comprise pulse signals, and the first switch and the second switch are turned on and off substantially in a complementary manner in response to the pulse signals supplied thereto. 6. The system of claim 5, further comprising a filter circuit, the filter circuit being operable to filter high frequency noise signals generated due to switching operations of the first switch and the second switch. 7. The system of claim 2, wherein the AC chopper comprises a boost circuit operable to boost the AC voltage from the AC voltage source, to allow the regulated AC voltage to be greater than the AC voltage so as to prolong light emission time of the first LED and the second LED for reducing total harmonic distortion and mitigating flicker phenomenon. 8. The system of claim 2, wherein the AC chopper comprises a buck-boost circuit operable to buck or boost the AC voltage from the AC voltage source, to allow the regulated AC voltage to be smaller or greater than the AC voltage from the AC voltage source. 9. The system of claim 2, further comprising a phase-cut dimming circuit connected between the AC voltage source and the AC driven LED unit, the phase-cut dimming circuit configured to provide a dimming control of the first LED and the second LED, wherein the phase-cut dimming circuit and the AC chopper are connected together in series between the AC voltage source and the AC driven LED unit, an input of the phase-cut dimming circuit connected to the AC voltage source and an output of the phase-cut dimming circuit connected to an input of the AC chopper. 10. The system of claim 1, wherein the AC voltage regulator comprises a dynamic voltage restorer (DVR), the DVR is operable to receive the AC voltage from the AC voltage source, and provide conditioning of the AC voltage applied to the first LED and the second LED. 11. The system of claim 1, further comprising a phase-cut dimming circuit coupled between the AC voltage regulator and the AC driven LED unit, the phase-cut dimming circuit is configured to provide a dimming control of the first LED and the second LED. 12. A system for driving an alternating current (AC) driven LED unit with an AC voltage originating from an AC voltage source, the AC driven LED unit having a first LED and a second LED arranged in reverse parallel, the system comprising: an alternating current (AC) voltage regulator, the AC voltage regulator being operable to receive the AC voltage originating from the AC voltage source, and to modulate the received AC voltage with pulse signals, a voltage level of the modulated AC voltage being adjusted by varying a duty cycle of the pulse signals to achieve a first dimming control of the first LED and the second LED;a phase-cut dimming circuit coupled to the AC voltage regulator, the phase-cut dimming circuit being operable to change a conduction angle of the received AC voltage to achieve a second dimming control of the first LED and the second LED; anda controller, the controller configured to receive a first feedback control signal from the AC voltage source indicating a voltage fluctuation of the AC voltage from the AC voltage source and generate a first control signal to the AC voltage regulator to maintain the modulated AC voltage at a predetermined level;the controller configured to receive a second feedback control signal from the AC driven LED unit indicating a voltage fluctuation of the regulated AC voltage from the AC voltage regulator and generate a second control signal to the AC voltage regulator to maintain the modulated AC voltage at the predetermined level. 13. The system of claim 12, further comprising a boost circuit operable to boost the AC voltage from the AC voltage source, to allow the modulated AC voltage to be greater than the AC voltage from the AC voltage source, so as to prolong light emission time of the first LED and the second LED for reducing total harmonic distortion and mitigating flicker phenomenon. 14. A method for driving an alternating current (AC) driven light emitting diodes (LED) unit, the AC driven LED unit comprising a first LED and a second LED, the first LED and the second LED being coupled in reverse parallel, the method comprising: receiving an AC voltage originating from an AC voltage source and generating a regulated AC voltage from an AC voltage regulator;using a controller to monitor fluctuations of the received AC voltage and the regulated AC voltage;applying the regulated AC voltage to the AC driven LED unit to drive the first LED and the second LED to emit light;wherein monitoring fluctuations of the received AC voltage and the regulated AC voltage by the controller comprises: receiving a first feedback control signal from the AC voltage source indicating a voltage fluctuation of the AC voltage from the AC voltage source and generating a first control signal to the AC voltage regulator to maintain the regulated AC voltage from the AC voltage regulator at a predetermined level; andreceiving a second feedback control signal from the AC driven LED unit to monitor a voltage fluctuation of the regulated AC voltage and generating a second control signal to the AC voltage regulator to maintain the regulated AC voltage at the predetermined level. 15. The method of claim 14, further comprising changing a conduction angle of the AC voltage originating from the AC voltage source by a phase-cut dimming circuit, so as to achieve a first dimming control of the first LED and the second LED. 16. The method of claim 14, wherein the step of regulating the received AC voltage comprises selectively chopping out at least a portion of the received AC voltage using an AC chopper. 17. The method of claim 16, wherein the AC chopper comprises a switch and wherein the step of chopping out at least a portion of the received AC voltage comprises turning on and off the switch to regulate the received AC voltage in response to pulse signals supplied to the switch. 18. The method of claim 17, further comprising varying a duty cycle of the pulse signals supplied to the switch to adjust a voltage level of the regulated AC voltage applied to the AC driven LED unit, so as to achieve a second dimming control of the first LED and the second LED. 19. The method of claim 14, further comprising boosting the received AC voltage by a boost circuit to allow the regulated AC voltage to be greater than the AC voltage received from the AC voltage source. 20. The method of claim 14, wherein the AC voltage regulator comprises a dynamic voltage restorer and wherein the method further comprises providing conditioning of the AC voltage applied to the AC driven LED unit by the dynamic voltage restorer.