Switch control systems for light emitting diodes and methods thereof

1. A system for controlling one or more light emitting diodes, the system comprising:

a current generator configured to generate a first current flowing through the one or more light emitting diodes, the one or more light emitting diodes being configured to receive a rectified voltage generated by a rectifying bridge coupled to a TRIAC dimmer;

a bleeder configured to receive the rectified voltage; and

a controller configured to:

receive a sensing voltage from the current generator, the sensing voltage indicating a magnitude of the first current;

receive an input voltage generated by a voltage divider, the voltage divider being configured to receive the rectified voltage, the input voltage indicating a magnitude of the rectified voltage; and

output a control signal to the bleeder;

wherein the controller is further configured to:

generate the control signal to turn off the bleeder if the sensing voltage and the input voltage satisfy a first condition so that the bleeder does not generate a second current, the second current being larger than zero in magnitude; and

generate the control signal to turn on the bleeder if the sensing signal and the input voltage satisfy a second condition so that the bleeder generates the second current;

wherein the second condition is different from the first condition;

wherein the controller is further configured to:

generate the control signal at a first logic level from a first time to a second time, during which the sensing voltage is smaller than a first reference voltage in magnitude and the input voltage is smaller than a second reference voltage in magnitude;

generate the control signal at a second logic level from the second time to a third time, during which the sensing voltage is larger than the first reference voltage in magnitude and the input voltage is larger than the second reference voltage in magnitude;

generate the control signal at the second logic level from the third time to a fourth time, during which the sensing voltage is smaller than the first reference voltage in magnitude and the input voltage is larger than the second reference voltage in magnitude; and

generate the control signal at the first logic level from the fourth time to a fifth time, during which the sensing voltage is smaller than the first reference voltage in magnitude and the input voltage is smaller than the second reference voltage in magnitude;

wherein the first logic level and the second logic level are different.

2. The system of claim 1 wherein the voltage divider includes multiple resistors connected in series and biased between the rectified voltage and a ground voltage.

3. The system of claim 1 wherein the controller is further configured to:

generate the control signal at the first logic level to turn on the bleeder so that the bleeder generates the second current; and

generate the control signal at the second logic level to turn off the bleeder so that the bleeder does not generate the second current.

4. The system of claim 1 wherein the rectifying bridge is coupled to the TRIAC dimmer through a fuse.

5. A method for controlling one or more light emitting diodes, the method comprising:

generating a first current flowing through one or more light emitting diodes, the one or more light emitting diodes being configured to receive a rectified voltage generated by a rectifying bridge coupled to a TRIAC dimmer;

receiving a sensing voltage, the sensing voltage indicating a magnitude of the first current;

receiving an input voltage, the input voltage indicating a magnitude of the rectified voltage; and

outputting a control signal to a bleeder;

wherein the outputting the control signal to the bleeder includes:

generating the control signal to turn off the bleeder if the sensing voltage and the input voltage satisfy a first condition so that the bleeder does not generate a second current, the second current being larger than zero in magnitude; and

generating the control signal to turn on the bleeder if the sensing signal and the input voltage satisfy a second condition so that the bleeder generates the second current;

wherein the second condition is different from the first condition;

wherein the outputting the control signal to the bleeder further includes:

generating the control signal at a first logic level from a first time to a second time, during which the sensing voltage is smaller than a first reference voltage in magnitude and the input voltage is smaller than a second reference voltage in magnitude;

generating the control signal at a second logic level from the second time to a third time, during which the sensing voltage is larger than the first reference voltage in magnitude and the input voltage is larger than the second reference voltage in magnitude;

generating the control signal at the second logic level from the third time to a fourth time, during which the sensing voltage is smaller than the first reference voltage in magnitude and the input voltage is larger than the second reference voltage in magnitude; and

generating the control signal at the first logic level from the fourth time to a fifth time, during which the sensing voltage is smaller than the first reference voltage in magnitude and the input voltage is smaller than the second reference voltage in magnitude;

wherein the first logic level and the second logic level are different.