Continuous step driver

1. A light emitting diode (LED) lamp, comprising:

an LED cluster comprising a plurality of LED groups arranged in series;

a power source configured to provide an input power to the LED cluster; and

a driving unit configured to adjust a number of the LED groups connected to a current path of the LED cluster in series based on the input power to the LED cluster,

wherein the plurality of LED groups comprise: a first LED group connected to the power source; and a second LED group connected to the first LED group in series;

wherein the driving unit comprises:

a plurality of switches, comprising: a first switch coupled between an output of the first LED group and ground; and a second switch coupled between an output of the second LED group and ground; and

a controller configured to turn on one of the first and second switches individually based on the input power to the LED cluster;

wherein the controller comprises: a first input connected to the power source to detect the input power; a first output connected to the first switch to turn on or off the first switch; and a second output connected to the second switch to turn on or off the second switch;

wherein the controller is further configured to compare the input power to a first threshold level for turning on the first LED group only and a second threshold level for turning on the first and second LED groups simultaneously; and

wherein the controller is further configured to turn on the first switch only when the input power is equal to or larger than the first threshold level and less than the second threshold level, and turn off the first switch and turn on the second switch when the input power is greater than the second threshold level.

2. The LED lamp of claim 1 , wherein the input power has a sinusoidal waveform.

3. The LED lamp of claim 1 , wherein the plurality of LED groups further comprise a third LED group connected to the second LED group in series, the driving unit further comprises a third switch coupled between an output of the third LED group and the ground, and the controller further comprises a third output connected to the third switch to turn on or off the third switch.

4. The LED lamp of claim 3 , wherein the driving unit is further configured to compare the input power to a third threshold level for turning on the first, second and third LED groups simultaneously, and connect the first, second and third LED groups in series to the current path of the LED cluster when the input power is equal to or larger than the third threshold level.

5. The LED lamp of claim 1 , wherein the plurality of LED groups and the plurality of switches have the same number.

6. The LED lamp of claim 1 , wherein the driving unit is further configured to adjust a number of the LED groups connected in series to the current path of the LED cluster based on at least one of the input power to the LED cluster and an output current from the LED cluster.

7. The LED lamp of claim 6 , wherein the controller further comprises a second input terminal connected to the plurality of switches to detect the output current therefrom.

8. A method of operating a light emitting diode (LED) cluster, comprising:

providing an input power to the LED cluster comprising a plurality of LED groups connectable in series;

detecting the input power; and

adjusting a number of the LED groups connected in series to a current path of the LED cluster based on the detected input power,

wherein the plurality of LED groups comprise a first LED group receiving the input power and a second LED group connected to the first LED group in series; and

wherein the adjusting a number of the LED groups comprises: comparing the input power to a first threshold level for turning on the first LED group only and a second threshold level for turning on the first and second LED groups connected in series; connecting only the first LED group to the current path of the LED cluster when the input power is equal to or larger than the first threshold level and less than the second threshold level; and connecting the first and second LED groups to the LED current path in series when the input power is greater than the second threshold level.

9. The method of claim 8 , wherein the input power has a sinusoidal waveform.

10. The method of claim 8 , wherein the plurality of LED groups further comprise a third LED group connected to the second LED group in series,

wherein the adjusting a number of the LED groups further comprises:

comparing the input power to a third threshold level for turning on the first, second and third LED groups connected in series; and

connecting the first, second and third LED groups to the LED current path in series when the input power is equal to or larger than the third threshold level.

11. The method of claim 8 , further comprises adjusting a number of the LED groups connected in series to the LED current path based on at least one of the input power and an output current from the LED cluster.

12. The method of claim 11 , wherein adjusting a number of LED groups connected in series to the current path comprises:

detecting the output current from the LED cluster;

comparing the output current to one or more current levels; and

adjusting a number of the LED groups connected to the LED current path in series based on comparison between the detected LED output and the one or more current levels.