The present invention is directed to integrated circuits. More particularly, the invention provides lighting systems and methods for constant current control in various operation modes. Merely by way of example, the invention has been applied to one or more light emitting diodes. But it would be recognized that the invention has a much broader range of applicability.
Generally, a conventional lighting system for light emitting diodes (LEDs) often uses a floating Buck converter. This type of LED lighting system usually is cost effective with compact size. FIG. 1 is a simplified diagram showing a conventional LED lighting system with a Buck converter. The lighting system 100 includes a pulse-width-modulation (PWM) controller 110, a power switch 120, a diode 130, an inductor 140, capacitors 150 and 152, and a sensing resistor 160. Additionally, the lighting system 100 receives an input voltage and provides a lamp current and a lamp voltage to one or more LEDs 190.
As shown in FIG. 1, the power switch 120 includes terminals 122, 124, and 126. The PWM controller 110 outputs a drive signal 112 and receives a current sensing signal 114. The drive signal 112 corresponds to a switching period (e.g., Ts). For example, the power switch 120 is a MOS transistor. In another example, the power switch 120 is a bipolar transistor (e.g. an NPN bipolar transistor). In yet another example, the power switch 120 is an insulated gate bipolar transistor (IGBT).
It is highly desirable to improve the techniques of constant current control, so that a constant lamp current can be achieved in the DCM mode, the CCM mode and the critical conduction mode (CRM), and both high power factor and precision control can be realized.