Control circuit, led driving system and control method thereof

An LED driving system comprising:

• an LED;
• a power transistor coupled in series with the LED, wherein a first terminal of the serially coupled power transistor and LED is coupled to an input power terminal having an input voltage, and a second terminal of the serially coupled power transistor and LED is coupled to a reference ground;
• and
• a control circuit coupled to a control end of the power transistor for regulating current flowing through the LED, wherein the control circuit has an input coupled to a dimming signal, and when a representative value of the dimming signal is higher than a first threshold, the control circuit regulates the amplitude of the current flowing through the power transistor based on the dimming signal, and when the representative value of the dimming signal is lower than a second threshold, the control circuit regulates the time of the current flowing through the power transistor based on the dimming signal, and wherein the second threshold is not higher than the first threshold.

A control method for controlling current flowing through a load, the load coupled in series with a power transistor, the method comprising:

• receiving a dimming signal;
• regulating the amplitude of the current flowing through the power transistor when the representative value of the dimming signal is higher than a first threshold;
• and
• regulating the time duration of the current flowing through the power transistor when the representative value of the dimming signal is lower than a second threshold, wherein the first threshold is equal to or higher than the second threshold.