Two-terminal current controller and related LED lighting device

1. A light-emitting diode (LED) lighting device with overvoltage protection, comprising:

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

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

a first impedance device for limiting the first current or the second current within a first predetermined range when a voltage established across the first luminescent device and the second luminescent device exceeds a first predetermined value;

a first two-terminal current controller coupled in parallel to the first luminescent device and in series to the second luminescent device and configured to regulate the second current according to a voltage established across the two-terminal current controller, wherein:

during a rising period of a rectified alternative-current (AC) voltage when the voltage established across the first luminescent device does not exceed a first voltage, the first two-terminal current controller operates in a first mode;

during the rising period when the voltage established across the first luminescent device exceeds the first voltage but does not exceed a second voltage, the first two-terminal current controller operates in a second mode;

during the rising period when the voltage established across the first luminescent device exceeds the second voltage, the first two-terminal current controller operates in a third mode; and

the first two-terminal current controller includes:

a current limiting unit configured to:

conduct a third current associated with the rectified AC voltage, regulate the third current according to the voltage established across the first luminescent device and maintain the first current at zero when the first two-terminal current controller operates in the first mode;

conduct the third current, maintain the third current at a second predetermined value larger than zero and maintain the first current at zero when the first two-terminal current controller operates in the second mode; and

switch off for equalizing the first current and the second current when the first two-terminal current controller operates in the third mode.

2. The LED lighting device of claim 1 , wherein when the voltage established across the first two-terminal current controller is larger than the first voltage and does not exceed a third voltage during a falling period of the rectified AC voltage, the first two-terminal current controller is turned on for maintaining the first current at substantially zero and setting the second current and the third current to the second predetermined value, and the third voltage is larger than the second voltage.

3. The LED lighting device of claim 2 , wherein the first two-terminal current controller comprises:

a switch configured to conduct the third current according to a turn-on voltage;

a control circuit configured to provide the turn-on voltage according to a first control signal and a second control signal;

a current-detecting circuit configured to determine whether the voltage established across the first two-terminal current controller is larger than the first voltage according to the third current, thereby providing the first control signal accordingly; and

a voltage-detecting circuit configured to determine relationships between the voltage established across the first two-terminal current controller, the second voltage and the third voltage, identify the corresponding rising or falling period, and provide the second control signal accordingly.

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

when the current-detecting circuit determines that the voltage established across the first two-terminal current controller does not exceed the first voltage, the switch regulates the third current according to the turn-on voltage; and

when the current-detecting circuit determines that the voltage established across the first two-terminal current controller is larger than the first voltage, the switch limits the third current to the second predetermined value according to the turn-on voltage.

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

when the voltage-detecting circuit determines that the voltage established across the first two-terminal current controller is larger than the first voltage and does not exceed the second voltage during the rising period, the switch limits the third current to the second predetermined value according to the turn-on voltage and maintains the first current at substantially zero; and

when the voltage-detecting circuit determines that the voltage established across the first two-terminal current controller is larger than the first voltage and does not exceed the third voltage which is larger than the second voltage during the falling period, the switch limits the third current to the second predetermined value according to the turn-on voltage and maintains the first current at substantially zero.

6. The LED lighting device of claim 3 , wherein the first two-terminal current controller is configured to regulate the third current according to the voltage established across the first two-terminal current controller, so that a relationship between the voltage established across the first two-terminal current controller and the third current matches a characteristic when the switch operates in a specific operational region.

7. The LED lighting device of claim 1 , wherein a barrier voltage for turning on the first two-terminal current controller is smaller than a barrier voltage for turning on the first luminescent device.

8. The LED lighting device of claim 1 , wherein each luminescent device includes a plurality of LEDs coupled in series.

9. The LED lighting device of claim 1 , wherein the first impedance device includes a resistor or a capacitor.

10. The LED lighting device of claim 1 , wherein the first impedance device is coupled in series to the first luminescent device and the second luminescent device.

11. The LED lighting device of claim 10 , wherein the first two-terminal current controller is coupled in parallel to the serially-coupled first luminescent device and the first impedance device.

12. The LED lighting device of claim 10 , further comprising:

a second two-terminal current controller coupled in series to the first two-terminal current controller and the second luminescent device and configured to regulate the second current according to a voltage established across the second two-terminal current controller, wherein the first impedance device is coupled in parallel to the second two-terminal current controller.

13. The LED lighting device of claim 1 , further comprising:

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;

a second two-terminal current controller coupled in parallel to the third luminescent device and in series to the first two-terminal current controller and the second luminescent device and configured to regulate the second current according to a voltage established across the second two-terminal current controller;

a second impedance device for limiting the fourth current within a second predetermined range when a voltage established across the first to third luminescent devices exceeds a second predetermined value, wherein:

the first impedance device is coupled in parallel to the first two-terminal current controller and coupled in series to the first luminescent device; and

the second impedance device is coupled in parallel to the second two-terminal current controller and coupled in series to the second luminescent device.

14. The LED lighting device of claim 10 , wherein the first impedance device comprises:

a second two-terminal current controller coupled in series to the first two-terminal current controller and configured to regulate the second current according to a voltage established across the second two-terminal current controller.

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

16. The LED lighting device of claim 15 wherein the power supply circuit includes an AC-AC voltage converter.

17. The LED lighting device of claim 1 , wherein the first luminescent device, the second luminescent device, the first impedance device and the first two-terminal current controller are disposed on a same circuit board.