High efficiency LED drivers with high power factor

A light-emitting diode (LED) driver configured to drive an LED device, the LED driver comprising:

• a) a rectifier bridge configured to receive an AC input voltage source, and to provide a first input voltage and a second input voltage;
• b) an LED current detection circuit coupled to said LED device in series between said second input voltage and a ground, wherein said LED current detection is configured to generate a feedback signal that represents an error between a driving current and an expected driving current of said LED device;
• c) a power stage circuit having a power switch, wherein a first power switch terminal is coupled to said first input voltage, and a second power switch terminal is directly connected to said ground;
• d) a control circuit coupled to said LED current detection circuit and said power stage circuit, wherein said control circuit shares said ground with said power stage circuit, and said control circuit is configured to generate a control signal according to said feedback signal and a drain-source voltage of said power switch, wherein said control signal is configured, in each switch period, to turn on said power switch when said drain-source voltage reaches a low level, and to turn off said power switch after a fixed time interval based on said feedback signal;
• and
• e) wherein said power switch is a composite power switch formed by series connected first and second power switches, wherein a first power terminal of said first power switch is configured as a first power terminal of said composite power switch, a second power terminal of said second power switch is configured as a second power terminal of said composite power switch, a control terminal of said second power switch is configured as a control terminal of said composite power switch, and a voltage reference is configured between said control terminal of said first power switch and said second power terminal of said second power switch.