It should be understood that the function of the reference voltage adjustment circuit in this example may be achieved by other circuit structures, such as controlling the linear drive circuit based on predetermined reference voltage REF1 when the conduction angle signal is greater than angle threshold DT1, controlling the linear drive circuit based on predetermined reference voltage REF2 when the conduction angle signal is less than angle threshold DT2, and controlling the linear drive circuit based on a reference voltage changing with the conduction angle signal when the conduction angle signal is not greater than the first angle threshold and not less than the second angle threshold. It should further be understood that the reference voltage may be adjusted in other manners than that described in particular embodiments, as long as the reference voltage can be decreased when the conduction angle signal is relatively small.

In this example, the conduction angle signal may be acquired by detecting the direct current bus voltage, and the reference voltage indicating a desired value of the drive current can be adjusted based on the conduction angle signal, such that the reference voltage is low when the conduction angle signal is less than the predetermined value, and the reference voltage returns to a normal voltage when the conduction angle signal is large. The linear drive circuit can be controlled based on the reference voltage that changes, to decrease the drive current flowing through the LED load in the case that the conduction angle signal is small, in order to effectively reduce the current ripple.