Light-emitting diode lighting device having multiple driving stages

1. A light-emitting diode (LED) lighting device having multiple driving stages, comprising:

a first driving stage including:

a first luminescent device for providing light according to a first current; and

a first current controller coupled in parallel with the first luminescent device and configured to conduct a second current according to a voltage established across the first current controller and regulate the second current so that a sum of the first current and the second current does not exceed a first value; and

a second driving stage including:

a second luminescent device coupled in series to the first luminescent device for providing light according to a third current; and

a second current controller coupled in series to the second luminescent device and configured to regulate the third current so that the third current does not exceed a second current setting which is larger than the first value, wherein each of the first and second luminescent devices includes one LED or multiple LEDs.

2. The LED lighting device of claim 1 , wherein:

during a rising period of a rectified alternative-current (AC) voltage when the voltage established across the first current controller does not exceed a first voltage, the first current controller operates in a first mode in which the second current increases with the rectified AC voltage;

during the rising period when the voltage established across the first current controller exceeds the first voltage and the second current is larger than zero, the first current controller operates in a second mode in which the sum of the first current and the second current is maintained at the first value; and

during the rising period when the voltage established across the first current controller exceeds the first voltage and the second current is equal to zero, the first current controller operates in a third mode in which the first current controller is turned off.

3. The LED lighting device of claim 2 , wherein:

during the rising period when the voltage established across the first current controller exceeds the first voltage but is smaller than a turn-on voltage of the first luminescent device, the first current controller is configured to operates in the second mode by clamping the second current at the first value; and

during the rising period when the voltage established across the first current controller exceeds the turn-on voltage of the first luminescent device, the first current controller is configured to operates in the second mode by reducing the second current as the first current increases so that the sum of the first current and the second current is maintained at the first value.

4. The LED lighting device of claim 2 , wherein:

during a falling period of the rectified AC voltage when the voltage established across the first current controller does not exceed the first voltage, the first current controller operates in the first mode in which the second current decreases with the rectified AC voltage;

during the falling period when the voltage established across the first current controller exceeds the first voltage and the second current is larger than zero, the first current controller operates in the second mode in which the sum of the first current and the second current is maintained at the first value; and

during the falling period when the voltage established across the first current controller exceeds the first voltage and the second current is equal to zero, the first current controller operates in the third mode in which the first current controller is turned off.

5. The LED lighting device of claim 4 , wherein:

during the falling period when the voltage established across the first current controller exceeds the first voltage but is smaller than the turn-on voltage of the first luminescent device, the first current controller is configured to operates in the second mode by clamping the second current at the first value; and

during the falling period when the voltage established across the first current controller exceeds the turn-on voltage of the first luminescent device, the first current controller is configured to operates in the second mode by increasing the second current as the first current decreases so that the sum of the first current and the second current is maintained at the first value.

6. The LED lighting device of claim 2 , wherein the first current controller includes:

a first current sensor configured to provide a first feedback voltage which is associated with the sum of the first current and the second current;

a first adjustable current source configured to:

conduct the second current according to the rectified AC voltage when the first current controller operates in the first mode;

regulate the second current according to the first feedback voltage when the first current controller operates in the second mode; and

switch off when the first current controller operates in the third mode.

7. The LED lighting device of claim 6 , wherein:

the first adjustable current source includes:

a voltage generator configured to provide a reference voltage;

an operational amplifier configured to provide a control voltage according to a difference between the reference voltage and the first feedback voltage, the operational amplifier including:

a first input end coupled to the reference voltage;

a second input end coupled to the first feedback voltage; and

an output end for outputting the control voltage;

a transistor configured to conduct the second current according to the control voltage, the transistor including:

a first end coupled to a first end of the first luminescent device;

a second end coupled to a second end of the first luminescent device; and

a control end coupled to the output end of the operational amplifier; and

the first current sensor includes a resistor having a first end coupled to the second end of the transistor and a second end coupled to a reference node.

8. The LED lighting device of claim 1 , wherein:

during a rising period of a AC voltage when the voltage established across the second current controller does not exceed a second voltage, the second current controller operates in a first mode in which the third current increases with the rectified AC voltage; and

during the rising period when the voltage established across the second current controller exceeds the second voltage, the second current controller operates in a second mode in which the third current is maintained at a second value.

9. The LED lighting device of claim 8 , wherein:

during a falling period of the rectified AC voltage when the voltage established across the second current controller does not exceed the second voltage, the second current controller operates in the first mode in which the third current decreases with the rectified AC voltage; and

during the falling period when the voltage established across the second current controller exceeds the second voltage, the second current controller operates in the second mode in which the third current is maintained at the second value.

10. The LED lighting device of claim 8 , wherein the second current controller includes:

a second current sensor coupled in series to the second luminescent device and configured to provide a second feedback voltage which is associated with the third current; and

a second adjustable current source configured to:

conduct the third current according to the rectified AC voltage when the second current controller operates in the first mode; and

regulate the third current according to the second feedback voltage when the second current controller operates in the second mode.

11. The LED lighting device of claim 10 , wherein:

the second adjustable current source includes:

a voltage generator configured to provide a reference voltage;

an operational amplifier configured to provide a control voltage according to a difference between the reference voltage and the second feedback voltage, the operational amplifier including:

a first input end coupled to the reference voltage;

a second input end coupled to the second feedback voltage; and

an output end for outputting the control voltage;

a transistor configured to conduct the third current according to the control voltage, the transistor including:

a first end coupled to an end of the second luminescent device;

a second end; and

a control end coupled to the output end of the operational amplifier; and

the second current sensor includes a resistor having a first end coupled to the second end of the transistor and a second end coupled to a reference node.

12. The LED lighting device of claim 1 , further comprising a third driving stage which includes:

a third luminescent device coupled in series to the first luminescent device and the second luminescent device for providing light according to a fourth current; and

a third current controller coupled in parallel with the third luminescent device and configured to conduct a fifth current according to a voltage established across the third current controller and regulate the fifth current so that a sum of the fourth current and the fifth current does not exceed a third value.

13. The LED lighting device of claim 1 further comprising a power supply circuit configured to provide a rectified AC voltage for driving the first luminescent device and the second luminescent device.

14. The LED lighting device of claim 13 wherein the power supply circuit includes an AC-AC voltage converter.

15. The LED lighting device of claim 1 wherein the second driving stage further comprises:

a transistor including:

a first end coupled to the second luminescent device;

a second end coupled to the second current controller; and

a control end; and

a voltage clamping circuit coupled to the control end of the transistor and configured to control the transistor according to a rectified AC voltage for driving the first luminescent device and the second luminescent device.