Two-terminal current controller and related LED lighting device

1. A two-terminal current controller for controlling a first current flowing through a load which is coupled in parallel with the two-terminal current controller, wherein:

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

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

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

during the rising period when the voltage established across the load drops to a third voltage smaller than the second voltage after exceeding the second voltage, the two-terminal current controller is configured to:

operate in the second mode when a difference between the second and third voltages exceeds a first hysteresis band; and

operate in the third mode when a difference between the second and third voltages does not exceed the first hysteresis band;

the two-terminal current controller includes:

a current limiting unit configured to:

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

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

switch off when the two-terminal current controller operates in the third mode.

2. The two-terminal current controller of claim 1 , wherein when the voltage established across the two-terminal current controller becomes smaller than a fourth voltage but is larger than the first voltage during a falling period of the rectified AC voltage, the two-terminal current controller operates in the second mode for maintaining the first current at substantially zero and setting the second current to the predetermined value, and the fourth voltage is larger than the second voltage.

3. The two-terminal current controller of claim 2 , wherein when the voltage established across the two-terminal current controller becomes larger than a fifth voltage which is larger than the fourth voltage after becoming smaller than the fourth voltage during the falling period of the rectified AC voltage, the two-terminal current controller is configure to:

operate in the third mode when a difference between the fourth and fifth voltages exceeds a second hysteresis band; and

operate in the second mode when a difference between the fourth and fifth voltages does not exceed the second hysteresis band.

4. The two-terminal current controller of claim 3 further comprising:

a first switch configured to conduct the second 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 two-terminal current controller is larger than the first voltage according to the second current, thereby providing the first control signal accordingly; and

a voltage-detecting circuit configured to determine relationships between the voltage established across the two-terminal current controller, the second voltage and the fourth voltage, thereby providing the second control signal accordingly.

5. The two-terminal current controller of claim 4 , wherein:

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

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

6. The two-terminal current controller of claim 4 , wherein:

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

7. The two-terminal current controller of claim 4 wherein the current-detecting circuit comprises:

a resistor coupled to the first switch for providing a feedback voltage according to the second current;

a second switch coupled in parallel to the resistor for adjusting an effective impedance of the resistor; and

a comparator for providing the first control signal according to a relationship between the feedback voltage and a reference voltage.

8. The two-terminal current controller of claim 4 wherein the voltage-detecting circuit comprises:

a voltage edge-detecting circuit configured to determine whether the voltage established across the two-terminal current controller is during the rising period or the falling period of the rectified AC voltage; and

a hysteresis comparator configured to determine a relationship between the voltage established across the two-terminal current controller, the second voltage and the third voltage.

9. The two-terminal current controller of claim 4 wherein the voltage-detecting circuit comprises:

a voltage edge-detecting circuit configured to determine whether the voltage established across the two-terminal current controller is during the rising period or the falling period of the rectified AC voltage;

a first hysteresis comparator configured to determine a relationship between the voltage established across the two-terminal current controller, the second voltage and the third voltage; and

a second hysteresis comparator configured to determine a relationship between the voltage established across the two-terminal current controller, the fourth voltage and the fifth voltage.

10. The two-terminal current controller of claim 1 , wherein the two-terminal current controller functions as a voltage-controlled device when operating in the first mode in which the voltage established across the two-terminal current controller does not exceed the first voltage, functions as a current source when operating in the second mode in which the voltage established across the two-terminal current controller is larger than the first voltage and does not exceed the second voltage, and functions as an open-circuited device when operating in the third mode in which the voltage established across the two-terminal current controller is larger than the second voltage.